Solar Energy

Projects for the

Evil Genius

Evil Genius Series

Bionics for the Evil Genius: 25 Build-it-Yourself

MORE Electronic Gadgets for the Evil Genius:

Projects

40 NEW Build-it-Yourself Projects

Electronic Circuits for the Evil Genius: 57 Lessons

101 Spy Gadgets for the Evil Genius

with Projects

123 PIC® Microcontroller Experiments for the Evil

Electronic Gadgets for the Evil Genius:

Genius

28 Build-it-Yourself Projects

123 Robotics Experiments for the Evil Genius

Electronic Games for the Evil Genius

PC Mods for the Evil Genius: 25 Custom Builds to

Electronic Sensors for the Evil Genius:

Turbocharge Your Computer

54 Electrifying Projects

Solar Energy Projects for the Evil Genius

50 Awesome Auto Projects for the Evil Genius

25 Home Automation Projects for the Evil Genius

50 Model Rocket Projects for the Evil Genius

Mechatronics for the Evil Genius:

25 Build-it-Yourself Projects

Solar Energy

Projects for the

Evil Genius

GAVIN D. J. HARPER

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DOI: 10.1036/0071477721

Professional

Want to learn more?

We hope you enjoy this

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please click here.

To the late Mr. P. Kaufman

who never failed to make science exciting

v

About the Author

Gavin Harper is a sus-

has written for a number of magazines and online

tainable technology

weblogs. His family continue to be bemused by

advocate and popular

his various creations, gadgets, and items of junk,

author of how-to books.

which are steadily accumulating. He holds a BSc.

His other publications

(Hons) Technology with the Open University, and

include 50 Awesome

has completed an MSc. Architecture: Advanced

Auto Projects for the

Environmental & Energy Studies with UeL/CAT.

Evil Genius, Model

He is currently studying towards a BEng. (Hons)

Rocket Projects for the Evil Genius, and Build

Engineering with the Open University, and filling

Your Own Car PC, all for McGraw-Hill … and if

in spare time with some postgraduate study at the

you enjoyed the chapter on fuel cells, his forth-

Centre for Renewable Energy Systems Technology

coming book Fuel Cell Projects for the Evil

at Loughborough University. He is rarely bored.

Genius will hit the shelves later this year. Gavin

Gavin lives in Essex, United Kingdom.

has had work published in the journal Science and

vi

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

For more information about this title, click here

Contents

Foreword by Willie Nelson

ix

Project 17: Build Your Own Parabolic

Acknowledgments

x

Dish Concentrator

69

Project 18: Experiment with Fresnel

Lens Concentrators

72

1 Why Solar?

1

9 Solar Pumping

75

2 The Solar Resource

9

Project 19: Build a Solar-Powered

3 Positioning Your Solar Devices

17

Fountain

76

Project 1: Build a Solar-Powered Clock! 20

Project 2: Build Your Own Heliodon

22

10 Solar Photovoltaics

81

Project 3: Experimenting with Light

Project 20: Grow Your Own “Silicon”

Rays and Power

25

Crystals

85

Project 21: Build Your Own

4 Solar Heating

27

“Thin-Film” Solar Cell

87

Project 4: Build Your Own Flat

Project 22: Experimenting with the

Plate Collector

31

Current–Voltage Characteristics

Project 5: Solar Heat Your Swimming

of a Solar Cell

92

Pool

33

Project 23: Experimenting with

Project 6: Useful Circuits for Solar

Current–Voltage Characteristics

Heating

35

of Solar Cells in Series

93

5 Solar Cooling

39

Project 24: Experimenting with

Project 7: Solar-Powered Ice-Maker

42

Solar Cells in Parallel

93

Project 25: Experiment with the

6 Solar Cooking

45

“Inverse Square Law”

94

Project 8: Build a Solar Hot Dog Cooker 46

Project 26: Experimenting with

Project 9: Build a Solar Marshmallow

Different Types of

Melter

48

Light Sources

96

Project 10: Cook Eggs on Your Driveway

Project 27: Experimenting with Direct

Using the Sun

49

and Diffuse Radiation

96

Project 11: Build a Solar Cooker

50

Project 28: Measurement of

Project 12: Build a Solar Camping

“Albedo Radiation”

99

Stove

51

7 Solar Stills

55

11 Photochemical Solar Cells

105

Project 13: Build a Window-Sill

Project 29: Build Your Own

Demonstration Solar Still

56

Photochemical Solar Cell

107

Project 14: Build a Pit-Type Solar Still

57

12 Solar Engines

113

Project 15: Build a Solar Basin Still

58

Project 30: Build a Solar Bird

8 Solar Collectors

61

Engine

113

Project 16: Build Your Own “Solar

Project 31: Make a Radial Solar

Death Ray”

64

Can Engine

116

vii

13 Solar Electrical Projects

119

Project 43: Build Your Own Solar

Project 32: Build Your Own Solar

Airship

146

Battery Charger

119

16 Solar Robotics?

149

Project 33: Build Your Own Solar

Project 44: Assembling Your

Phone Charger

120

Photopopper Photovore

153

Project 34: Build Your Own

Solar-Powered Radio

123

17 Solar Hydrogen Partnership

161

Project 35: Build Your Own

Project 45: Generating Hydrogen

Solar-Powered Torch

124

Using Solar Energy

164

Project 36: Build Your Own Solar-

Project 46: Using Stored Hydrogen

Powered Warning Light

126

to Create Electricity

168

Project 37: Build Your Own Solar-

18 Photosynthesis—Fuel from the Sun

171

Powered Garden Light

127

Project 47: Proving Biofuel Requires

14 Tracking the Sun

129

Solar Energy

177

Project 38: Simple Solar Tracker

130

Project 48: Proving Biofuel Requires

Water

177

15 Solar Transport

135

Project 49: Looking at the Light-

Project 39: Build Your Own Solar Car

137

Absorption Properties of

Project 40: Hold Your Own Solar

Chlorophyll

178

Car Race

142

Project 50: Make Your Own Biodiesel

180

Project 41: Souping Up Your

Solar Vehicle

143

Appendix A: Solar Projects on the Web

185

Project 42: Supercharge Your

Appendix B: Supplier’s Index

188

Solaroller

143

Index

195

Contents

viii

Foreword

Gavin Harper’s book Solar Energy Projects for the

solar energy into layman’s terms, while including

Evil Genius is a “must read” for every sentient

examples of do-it-yourself projects which make

human on this planet with a conscience, a belief in

the practical applications obvious, gives this boy

the bottom line, or a simple belief in the future of

genius the “street cred” (industry savvy) he so very

humanity.

much deserves.

At a time when such a book should be offered

This is a “how-to” book, which debunks the

as suggested reading for the 19-year-old

myth that “these things are decades away,” and,

Gavin Harper, he’s bucking the trend by actually

without exception, should be in every classroom

being the author. Okay, so he’s written a book on

under the same sun.

solar energy you say, big deal you say. You would

So crack this book, turn on your solar light, and

be wrong. Not only is this Gavin’s fourth book, it

sit back for a ride into our “present”… as in “gift”

is nothing short of pure genius.

from God.

To be able to write about solar energy is one thing.

But to possess the ability to put the knowledge of

Willie Nelson

ix

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Acknowledgments

There are always a lot of thank-yous to be said with

A massive thank-you to Kay Larson, Quinn

any book, and this one is no exception. There are a

Larson, Matt Flood, and Jason Burch at

lot of people that I would like to thank immensely

Fuelcellstore.com for helping me find my way

for material, inspiration, ideas, and help—all of

with fuel cells, and for being inspirational and let-

which have fed in to make this book what it is.

ting me experiment with their equipment. It would

also be wrong not to mention H the cat, who was

2

First of all, a tremendous thank-you to the staff

terrific company throughout the process of learning

and students of the MSc. Architecture: Advanced

about fuel cells.

Environmental & Energy Studies course at the

Centre for Alternative Technology, U.K. I never

Also, many thanks to Annie Nelson, and Bob

cease to be amazed by the enthusiasm, passion,

and Kelly King of Pacific Biodiesel for providing

and excitement members of the course exude.

me with some amazing opportunities to learn about

biodiesel.

I’d like to say a big thank-you to Dr. Greg P.

Smestad, for his help and advice on photochemical

Thanks to Michael Welch at Home Power

cells. Dr. Smestad has taken leading-edge research,

magazine, and also to Jaroslav Vanek, Mark

straight from the lab, and turned it into an accessi-

“Moth” Green, and Steven Vanek, the designers of

ble experiment that can be enjoyed by young sci-

the fantastic solar ice-maker featured in Chapter 5.

entists of all ages. I would also like to thank Alan

Their solar-powered ice-maker has already proven

Brown at the NASA Dryden Flight Research

its immense worth in the developing world … and

Center for the information he provided on solar

if you guys at home start building them at home

flight for Chapter 15.

and switching off your air-con and freezers, they

stand to be a big hit in the developed world as well.

Also a big thank-you to Ben Robinson and the

guys at Dulas Ltd. for their help in procuring

A big thank-you to my grandfather, who has

images, and for setting a great example by show-

seen the mess upstairs and manages to tolerate it,

ing how companies can be sustainable and ethical.

to my grandmother who hears about the mess

upstairs and does not realize its magnitude, and to

I’d also like to thank Hubert Stierhof for sharing

Ella who does a good job of keeping the mess

his ideas about solar Stirling engines, and Jamil

within sensible limits—and knows when to keep

Shariff for his advice on Stirling engines and for

quiet about it. Thanks are also long overdue to my

continuing to be inspirational.

dad, who is always immensely helpful in providing

practical advice when it comes to how to build

Thanks also to Tim Godwin and Oliver

things, and to my mum who manages to keep life

Sylvester-Bradley at SolarCentury, and to Andrew

going when I have got my head in a laptop.

Harris at Schuco for sharing with me some of their

solar installations.

A huge thank-you to Judy Bass, my fantastic

editor in New York who has been great throughout

An immense thank-you to Dave and Cheryl

the trials and tribulations of bringing this book to

Hrynkiw and Rebecca Bouwseman at Solarbotics

print, and to the tremendous Andy Baxter (and the

for sharing their insight on little solar-powered

rest of his team at Keyword) who has managed to

critters, and for providing the coupon in the back

stay cool as a cucumber and provide constant reas-

of the book so that you can enjoy some of their

surance throughout the editing process.

merchandise for a little less.

x

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Chapter 1

Why Solar?

So already we have seen that we can meet 82%

Our energy

of our energy needs with solar technologies!

The next 13% of our energy is used to provide

In everyday life, we consume a tremendous

electrical power for our lights and home. In

amount of energy. Our lives are styled around

Chapter 10 on solar photovoltaics, we will see how

consumption—consumption of natural resources

we can produce clean electricity from solar energy

and consumption of energy.

with no carbon emissions.

Figure 1-1 dramatically illustrates where all of

The remaining 5% is all used for cooking—

this energy goes.

again we will see in this book how easy it is to

These figures are for a U.K. lifestyle, but we can

cook with the power of the sun!

take this as being representative for people who

So we have seen that all of our energy needs can

live in the “developed world.”

be met with solar technologies.

The bulk of our energy consumption goes on

space heating—58%—this is something that can

easily be provided for with passive solar design.

Why solar?

Next is water heating, which requires 24% of the

energy which we use—again, we will see in this

The short answer to this question, albeit

book how we can easily heat water with solar energy.

not the most compelling is “Why not solar?”

Figure 1-1

Domestic energy use. Information extracted from DTI publication “Energy Consumption in the United Kingdom.” You can download this information from www.dti.gov.uk.

1

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Solar energy is clean, green, free, and best of all,

isn’t going to be going anywhere for about the next

Renewable versus

five billion years—now I don’t know about you,

nonrenewable

but when the sun does eventually expire, I for one

will be pushing up the daisies, not looking on with

At present, the bulk of our energy comes from

my eclipse glasses.

fossil fuels—gas, coal, and oil. Fossil fuels are

For the longer, more compelling answer, you are

hydrocarbons, that is to say that if we look at

going to have to read the rest of this chapter. At the

them chemically, they are wholly composed of

end, I hope that you will be a solar convert and be

hydrogen and carbon atoms. The thing about

thinking of fantastic ways to utilize this amazing,

hydrocarbons is that, when combined with the

environmentally friendly, Earth-friendly technology.

oxygen in the air and heat, they react exothermi-

If we look at North America as an example, we

cally (they give out heat). This heat is useful,

can see that there is a real solar energy resource

and is used directly as a useful form of energy in

(Figure 1-2). While the majority of this is concen-

itself, or is converted into other forms of energy

trated in the West, there is still enough solar energy

like kinetic or electrical energy that can be used

to be economically exploited in the rest of the

to “do some work,” in other words, perform a

U.S.A.!

useful function.

Figure 1-2

North American solar resource. Image courtesy Department of Energy.

Why Solar?

2

Why Solar?

When the Industrial Revolution was in full-

So where did all these

swing Augustin Mouchout wondered whether the

supply of fossil fuels would be able to sustain the

fossil fuels come from . . .

Industrial Revolution indefinitely.

and can’t we get some

“Eventually industry will no longer find in

more?

Europe the resources to satisfy its prodigious

expansion. Coal will undoubtedly be used up.

OK, first of all, the answer is in the question—

What will industry do then?”

fossils. Fossil fuels are so named because they are

formed from the remains of animals and plants that

were around a loooooong time ago. The formation

of these fuels took place in the carboniferous period

Fossil fuel emissions

which in turn was part of the Paleozoic era, around

360 to 286 million years ago. This would have been

Take a peek at Figure 1-3. It is pretty shocking

an interesting time to live—the world was covered

stuff! It shows how our fossil fuel emissions have

in lots and lots of greenery, big ferns, lush verdant

increased dramatically over the past century—this

forests of plants. The oceans and seas were full of

massive amount of carbon dioxide in the atmos-

algae—essentially lots of small green plants.

phere has dire implications for the delicate balance

of our ecosystem and could eventually lead to run-

Although there are some coal deposits from

away climate change.

when T-Rex was king, in the late cretaceous period

around 65 million years ago, the bulk of fossil

fuels were formed in the carboniferous period.

Hubbert’s peak and

Peak Oil

So what happened to

make the fossil fuels?

Back in 1956 an American geophysicist by the

name of Marion King Hubbert presented a paper to

Well, the plants died, and over time, layers of rock

the American Petroleum Institute. He said that oil

and sediment and more dead stuff built up on top

production in the U.S.A. would peak toward the

of these carbon-rich deposits. Over many years, the

end of the 1960s, and would peak worldwide in the

tremendous heat and pressure built up by these

year 2000. In fact, U.S. oil production did peak at

layers compressed the dead matter

the beginning of the 1970s, so this wasn’t a bad

prediction; however, the rest of the theory contains

a dire warning.

The theory states that production of fossil fuels

We have only recently

follows a bell-shaped curve, where production

started to worry about

begins to gradually increase, then as the technol-

ogy becomes mainstream there is a sharp upturn in

fossil fuels—surely we

production, followed by a flattening off when pro-

have time yet?

duction has to continue against rising costs. As the

costs of extraction increase, production begins to

This is an incorrect assumption. For some time,

plateau, and then fall—falling sharply at first, and

people have prophesized the end of the fossil fuel age.

then rapidly.

3

Figure 1-3

How our fossil fuel emissions have increased.

This is illustrated in Figure 1-4.

This means that, if we have crossed the peak,

So have we crossed the

our supplies of fossil fuels are going to begin

peak, and is there any

to drop rapidly—when you think about how

reliant we are on fossil fuels, this means that

evidence to support this?

there is going to be a rapid impact on our way

of life.

The International Energy Agency has stated that

energy production is in decline in 33 out of the 48

largest world oil producers. So, probably yes.

In the same way that there is Peak Oil, there is

also Peak Coal, Peak Gas and Peak Uranium. All

of these resources are in finite supply and will not

last forever.

This means that those who believe that heavy

investment in nuclear is the answer might be

in for a shock. Nuclear has been touted by many

as a means of plugging the “energy hole” left

when fossil fuels run out; however, everyone

in the world is facing the same problems—if

everyone switches to nuclear power, the rate at

Why Solar? Figure 1-4 Depiction of the “Peak Oil” scenario.

which uranium is consumed will greatly increase.

4

Why Solar?

resources that can be exploited, when these run

A few other reasons

out we need to find alternatives, and where there

are no alternatives then we will surely be very

why nuclear is a dumb

stuck.

option

Nuclear power really is pretty dangerous—talking

Mitigating climate change

about nuclear safety is a bit of a myth. Nuclear

power stations are a potential target for terrorists,

It is now widely acknowledged that climate change

and if we want to encourage a clean, safe world,

is happening, and that it is caused by man-made nuclear is not the way to go.

events. Of course, there is always the odd scientist,

Nuclear makes bad financial sense. When the

who wants to wave a flag, get some publicity and

fledgling nuclear power industry began to build

say that it is natural and that there is nothing we

power stations, the industry was heavily subsi-

can do about it, but the consensus is that the

dized as nuclear was a promising new technology

extreme changes that we are seeing in recent times

that promised “electricity too cheap to meter.”

are a result of our actions over the past couple of

Unfortunately, those free watts never really materi-

hundred years.

alized—I don’t know about you, but my power

company has never thrown in a few watts produced

Sir David King, the U.K.’s Chief Scientific

cheaply by nuclear power. Solar on the other hand

Advisor says that climate change is “the most

is the gift that keeps on giving—stick some photo-

severe problem that we are facing today—more

voltaics on your roof and they will pump out free

serious even than the threat of terrorism.”

watts for many years to come with virtually zero

maintenance.

Decommissioning is another big issue—just

So how can we use solar

because you don’t know what to do with some-

thing when you finish with it isn’t an argument to

energy?

ignore it. Would you like a drum of nuclear waste

sitting in your garden? All the world round, we

When you start to think about it, it is surprising

haven’t got a clue where to stick this stuff. The

how many of the different types of energy sources

U.S.A. has bold plans to create Yucca mountain, a

around us actually come from the sun and solar-

repository for nuclear waste—but even if this hap-

driven processes. Take a look at Figure 1-5 which

pens, the problem doesn’t go away—it is simply

illustrates this.

consolidated.

We can see how all of the energy sources in this

figure actually come from the sun! Even the fossil

fuels which we are burning at an unsustainable rate

at the moment, actually originally came from the

Environmental

sun. Fossil fuels are the remains of dead animal

responsibility

and plant matter that have been subject to extreme

temperature and pressure over millions of years.

Until cheap accessible space travel becomes a

Those animals fed on the plants that were around

reality, and let’s face it, that’s not happening soon,

at the time (and other animals) and those plants

we only have one planet. Therefore, we need to

grew as a result of the solar energy that was falling

make the most of it. The earth only has so many

on the earth.

5

Figure 1-5

Energy sources. Image courtesy Christopher Harper.

Biomass therefore is a result of solar energy—

important to note that the hydrological cycle

additionally, biomass takes carbon dioxide out of

is driven by the sun. So we can say that hydro-

the atmosphere. When we burn it we simply put

power is also the result of a solar-driven

back the carbon dioxide that was taken out in the

process.

first place—the only carbon emissions are a result

Wind power might seem disconnected from solar

of processing and transportation.

energy; however, the wind is caused by air rushing

Looking at hydropower, you might wonder

from an area of high pressure to an area of low

Why Solar? how falling water is a result of the sun, but it is pressure—the changes in pressure are caused by

6

Why Solar?

the sun heating air, and so yet again we have

America in a position where it is dependent on oil

another solar-driven process!

imported from other countries—politically, this is

Tidal power is not a result of the sun—the tides

not the best position to be in. Next we look at hydro-

that encircle the earth are a result of the gravita-

power, which produces around 7% of America’s

tional pull that the moon has on the bodies of

electricity. Things like aluminum smelters, which

water that cover our planet. However, wave power

require large inputs of electricity, are often located

which has a much shorter period, is a result of

near to hydropower schemes because they produce

the wind blowing on the surface of the water—just

an abundance of cheap electricity. Finally the

as the wind is a solar-driven process, so is wave

“others” account for 5% of America’s electricity

power.

production.

It is these “others” that include things such as

solar power, wind powers and wave and tidal

power. It is this sector that we need to grow in

So where does our

order to make energy supply more sustainable and

energy come from at

decrease our reliance on fossil fuels.

the moment?

This book is primarily concerned with develop-

ment of the solar energy resource.

Let’s look at where the U.S.A. gets its energy

The nuclear lobby argue that nuclear is “carbon

from—as it is representative of many western

neutral” as the plants do not produce carbon diox-

countries.

ide in operation; however, this does not take into

If we look at the U.S.A.’s energy consumption,

account the massive input of energy used to con-

we can see (Figure 1-6) that most of our energy at

struct the plant, move the fuel, and decommission the

the moment is produced from fossil fuels. This is a

plant. All of this energy (generally speaking)

carbon-intensive economy which relies on imports

comes from high-carbon sources.

of carbon-based fossil fuels from other countries,

So we must look at the two remaining alternatives

notably the Middle East. Unfortunately, this puts

to provide our energy—hydro and “others.”

Figure 1-6

Where the United States’ energy comes from.

7

There are limits to how much extra hydroelectric

infrastructure that large hydro projects do. While

capacity can be built. Hydroelectricity relies on

they produce a lot less power, they are an interest-

suitable geographic features like a valley or basin

ing area to look at.

which can be flooded. Also, there are devastating

effects for the ecosystems in the region where the

hydro plant will be built, as a result of the large-

So all this is new right?

scale flooding which must take place to provide

the water for the scheme.

Nope . . . Augustin Mouchot, a name we will see a

Micro-hydro offers an interesting alternative.

couple of times in this book said in 1879:

Rather than flooding large areas, micro-hydro

“One must not believe, despite the silence of

schemes can rely on small dams built on small

modern writings, that the idea of using solar heat

rivers or streams, and do not entail the massive

for mechanical operations is recent.”

Why Solar?

8

Chapter 2

The Solar Resource

It has a diameter of 864,950 miles; again, if you

The sun

are working to metric standards that equates to

1.392 million km.

Some 92.95 × 106 miles away from us, or for those

Although the sun is incredibly far away—it is

working in metric 149.6 × 106 km away from us is

also tremendously huge! This means that although

the sun (Figure 2-1). To imagine the magnitude of

you would think that relatively little solar energy

this great distance, think that light, which travels at

reaches us, in fact, the amount of solar radiation

an amazing 299,792,458 meters per second, takes a

that reaches us is equal to 10,000 times the

total of 8.31 minutes to reach us. You might like to

annual global energy consumption. On average,

do a thought experiment at this point, and imagine

1,700 kWh per square meter is insolated every

yourself traveling in an airplane across America.

year.

At a speed of around 500 miles per hour, this

Now doesn’t it seem a silly idea digging miles

would take you four hours. Now, if you were trav-

beneath the earth’s surface to extract black rock

eling at the speed of light, you could fly around the

and messy black liquid to burn, when we have this

earth at the equator about seven and a half times in

amazing energy resource falling on the earth’s

one second. Now imagine traveling at that speed

surface?

for 8.31 minutes, and you quickly come to realize

As the solar energy travels on its journey to the

that it is a long way away.

earth, approximately 19% of the energy is

Not only is it a long way away, but it’s also

absorbed by the atmosphere that surrounds the

pretty huge!

earth, and then another 35% is absorbed by clouds.

Once the solar energy hits the earth, the journey

doesn’t stop there as further losses are incurred in

the technology that converts this solar energy to a

useful form—a form that we can actually do some

useful work with.

How does the sun work?

The sun is effectively a massive nuclear reactor.

When you consider that we have such an incredi-

bly huge nuclear reactor in the neighborhood

already, it seems ridiculous that some folks want to

build more!

The sun is constantly converting hydrogen to

Figure 2-1

The sun. Image courtesy NASA .

helium, minute by minute, second by second.

9

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

But what stops the sun from exploding in a

Starting from the center of the sun we have the

massive thermonuclear explosion?—simple

core, the radiative zone, the convective zone, the

gravity! The sun is caught in a constant struggle

photosphere, the chromosphere, and the corona.

between wanting to expand outwards as a result of

the energy of all the complex reactions occurring

The core

inside it, and the massive amount of gravity as a

result of its enormous amount of matter, which

The core of the sun possesses two properties which

wants to pull everything together.

create the right climate for nuclear fusion to

All of the atoms inside the sun are attracted to

occur—the first is incredibly high temperature

each other, this produces a massive compression

15 million degrees Celsius (I don’t envy the poor

which is trying to “squeeze” the sun inwards.

chap who had to stand there with a thermometer

Meanwhile, the energy generated by the nuclear

to take the reading) and the second is incredibly

reactions taking place is giving out heat and energy

high pressure. As a result of this nuclear fusion

which wants to push everything outwards. Luckily

takes place.

for us, the two sets of forces balance out, so the

In nuclear fusion, you take a handful of hydro-

sun stays constant!

gen nuclei—four in fact, smash them together and

end up with one helium nucleus.

There are two products of this process—gamma

Structure of the sun

rays which are high-energy photons and neutrinos,

one of the least understood particles in the uni-

Figure 2-2 illustrates the structure of the sun—now

verse, which possess no charge and almost no

let’s explain what some of those long words mean!

mass.

The Solar Resource Figure 2-2 The structure of the sun. Image courtesy NASA.

10

The Solar Resource

excited hydrogen atoms, which emit light toward

The radiative zone

the red wavelengths of the visible spectrum.

Next out from the core is the radiative zone. This

zone is so named because it is the zone that emits

The corona

radiation. A little bit cooler, the temperature in the

radiative zone ranges from 15 million to 1 million

The corona, which stretches for millions of miles

degrees Celsius (even at that temperature though,

out into space, is the outer layer of the sun’s

I still wouldn’t have liked to have been the one

atmosphere. The temperatures here get mighty hot,

holding the thermometer).

in fact up to a million degrees Celsius. Some of the

features on the surface of the sun can be seen in

What is particularly interesting about the

Figure 2-2, but they are described in more detail in

radiative zone, is that it can take millions of years

the next section and Figure 2-3.

for a photon to pass through this zone to get to the

next zone, aptly named the convective zone!

Features of the sun

The convective zone

Now we have seen the inner machinations of the

This zone is different, in that the photons now

sun, we might like to take a look at what goes on

travel via a process of convection—if you remem-

on the surface of the sun, and also outside it in the

ber high school physics, you will recollect that

immediate coronal region.

convection is a process whereby a body makes its

way to a region of lower temperature and lower

Coronal holes form where the sun’s magnetic

pressure. The boundary of this zone with the radia-

field lies. Solar flares, also known as solar promi-

tive zone is of the order of a million degrees

nences, are large ejections of coronal material into

Celsius; however, toward the outside, the tempera-

space. Magnetic loops suspend the material from

ture is only a mere 6,000°C (you still wouldn’t

these prominences in space. Polar plumes are

want to hold the thermometer even with asbestos

gloves).

The photosphere

The next region is called the photosphere. This is

the bit that we see, because this is the bit that

produces visible light. Its temperature is around

5,500°C which is still mighty hot. This layer,

although relatively thin in sun terms is still around

300 miles thick.

The chromosphere

Sounding like a dodgy nightclub, the chromo-

sphere is a few thousand miles thick, and the

temperature rises in this region from 6,000°C to

Figure 2-3

Features on the sun’s surface. Image

anywhere up to 50,000°C. This area is full of

courtesy NASA.

11

altogether smaller, thinner streamers that emanate

When we think about the earth and its orbit, we

from the sun’s surface.

can see how the earth rotates upon its axis, which

is slightly inclined in relation to the sun. As the

earth rotates at a constant speed, there will be

certain points in the earth’s orbit when the sun

The earth and the sun

shines for longer on a certain part of the earth—

and furthermore, because of the earth’s position in

Now we have seen what goes on at the source, we

space, that part of the world will tend to be nearer

now need to explore what happens after that solar

to the sun on average over the period of a day. This

energy travels all the way through space to reach

is why we get the seasons—this is illustrated in

the earth’s orbit.

Figure 2-4.

Outside the earth’s atmosphere, at any given

As a result of the sun appearing to be in a differ-

point in space, the energy given off by the sun

ent place in the sky, we may need to move our

(insolation) is nearly constant. On earth, however,

solar devices to take account of this. Figure 2-5

that situation changes as a result of:

illustrates how a flat plate collector may need to

●

The earth changing position in space

be moved at different times of the year to take

account of the change in the sun’s position in order

●

The earth rotating

to harness energy effectively.

●

The earth’s atmosphere (gases, clouds, and dust)

The gases in the atmosphere remain relatively

stable. In recent years, with the amount of pollu-

tion in the air, we have noticed a phenomenon

known as global dimming, where the particulate

So how can we harness

matter resulting from fossil fuels, prevents a small

solar energy?

fraction of the sun’s energy from reaching the

earth.

Thinking about it, more or less all of our energy

Clouds are largely transient, and pass from place

has come either directly or indirectly from the sun

to place casting shadows on the earth.

at one point or another.

The Solar Resource Figure 2-4 The sun and seasons.

12

The Solar Resource

Figure 2-5

The sun changes position depending on the time of year.

Solar power

the water’s gravitational potential energy and turn

it into electricity.

Solar-powered devices are the most direct way of

capturing the sun’s energy, harnessing it, and

Biomass

turning it into something useful. These devices

capture the sun’s energy and directly transform it

Rather than burning fossil fuels, there are certain

into a useful energy source.

crops that we can grow for energy which will

replace our fossil fuels. Trees are biomass, they

Wind power

produce wood that can be burnt. Sugarcane can

also be grown and be turned into bio-ethanol,

The heat from the sun creates convective currents

which can be used in internal combustion engines

in our atmosphere, which result in areas of high

instead of gasoline. Oils from vegetable plants can

and low pressure, and gradients between them. The

in many cases be used directly in diesel engines or

air rushing from place to place creates the wind,

reformed into biodiesel. The growth of all of these

and using large windmills and turbines, we can

plants was initiated by the sun in the first place,

collect this solar energy and turn it into something

and so it can be seen that they are derived from

useful—electricity.

solar energy.

Hydropower

Wave power

The sun drives the hydrological cycle, that is to say

Wave power is driven by the winds that blow over

the evaporation of water into the sky, and precipi-

the surface of large bodies of water. We have seen

tation down to earth again as rain. What this means

how the wind is produced from solar energy;

is that water which was once at sea level can end

however, we must be careful to distinguish wave

up on higher ground! We can collect this water at a

power from tidal power, which is a result of the

high place using a dam, and then by releasing the

gravitational attraction of the moon on a large

water downhill through turbines, we can release

body of water.

13

Figure 2-6

Harnessing renewable energy to meet our energy needs cleanly.

Figure 2-7

Solar energy being harnessed directly on the roofs of the eco-cabins at the Centre for Alternative Technology, U.K.

The Solar Resource

14

The Solar Resource

Fossil fuels

As we have seen, there are many ways in which

we can harness solar power. Figure 2-6 shows

You probably never thought that you would hear

some clean renewable ways in which we can

an environmentalist saying that fossil fuels are a

capture solar energy not only from solar panels,

form of solar energy—well think again! Fossil

but also from the power in the wind. Although not

fuels are in fact produced from the clean energy of

immediately apparent, the black pipeline that runs

the sun—at the end of the day, all they are is

through the picture is in fact a small-scale hydro

compressed plant matter which over millions of

installation—yet another instance of solar energy

years has turned into oil, gas, and coal—and herein

being harnessed (indirectly).

lies the problem. It took millions of years for these

This book focuses solely on “directly” capturing

to form, and they are soon exhausted if we burn

solar energy. In Figure 2-7 we can see a variety of

them at their present rate. So yes, they are a result

technologies being used to capture solar energy

of solar energy, but we must use them with care!

directly in a domestic setting.

15

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Chapter 3

Positioning Your Solar Devices

It is important to note that the position of the sun

It sounds like the destination for a pilgrimage for

in the sky changes from hour to hour, day to day,

solar junkies worldwide!

and year by year. While this might be interesting,

We can be fairly sure that the obelisks that they

it is not very helpful to us as prospective solar energy

erected, such as London’s Cleopatra’s needle

users, as it presents us with a bit of a dilemma—

(Figure 3-1), were used as some sort of device that

where exactly do we point our solar device?

indicated a time of day based on the position of

The ancients attributed the movement of the ball

the sun.

of fire in the sky to all sorts of phenomena, and

If you dig a stick into the ground, you will see

various gods and deities. However, we now know

that as the sun moves through the sky, so the

that the movement of the sun through the sky is as

shadow will change (Figure 3-2). In the morning

a result of the orbital motion of the earth, not as a

the shadow will be long and thin; however, toward

result of flaming chariots being driven through the

the middle of the day, the position of the shadow

sky on a daily basis!

not only changes, but the shadow shortens. Then

In this chapter, we are going to get to grips with

at the end of the day, the shadow again becomes

a couple of concepts—that the position of the sun

long.

changes relative to the time of the day, and also, that

Of course, this effect is caused by the earth spin-

that position is further influenced by the time of

ning on its axis, which causes the position of the

the year.

sun in the sky to change relative to our position on

the ground.

We will use this phenomena to great effect later

How the position of the

in our “sun-powered clock.”

sun changes over the day

The ancients were aware of the fact that the sun’s

position changed depending on the time of the day.

How the position of the

It has been speculated that ancient monuments

such as Stonehenge were built to align with the

sun changes over the

position of the sun at certain times of the year.

year

The position of the sun is a reliable way to help

us tell the time. The Egyptians knew this, the three

The next concept is a little harder to understand.

Cleopatra’s needles sited in London, Paris, and

The earth is slightly tilted on its axis; as the earth

New York were originally from the Egyptian city

rotates about the sun on its 3651⁄4-day cycle, differ-

of “Heliopolis” written in Greek as Ηλíου πóλις.

ent parts of the earth will be exposed to the sun for

The name of the city effectively meant “town

a longer or shorter period. This is why our days are

of the sun” and was the place of sun-worship.

short in the winter and long in the summer.

17

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Figure 3-1

Cleopatra’s needle—an early solar clock?

Positioning Your Solar Devices Figure 3-2 How shadows change with the time of day.

18

Positioning Your Solar Devices

The season in the northern hemisphere will be

sun shines from the north rather than the south . . .

exactly the opposite to that in the southern hemi-

obviously if your house is in the northern hemi-

sphere at any one time.

sphere, the sun will be in the south!

We can see in Figure 3-3 that because of this tilt,

This graphically demonstrates how the sun’s

at certain times of year, depending on your latitude

path in the sky changes relative to your plot at

you will receive more or less sunlight per day. Also

different times of year, as well as illustrating how

if you look at your latitude relative to the sun, you

our rules for solar positioning are radically different can see that as the earth rotates your angle to the

depending on what hemisphere we are in.

sun will be different at any given time of day,

What does this mean for us in practice?

depending on the season.

Essentially, it means that we need to change the

We can see in Figure 3-4 an example house in

position of our solar devices if we are to harness

the southern hemisphere—here we can see that the

the most solar energy all year round.

Figure 3-3

How the earth’s position affects the seasons.

Figure 3-4

Seasonal variation of the sun’s position.

19

Project 1: Build a Solar-Powered Clock!

You will need

Tools

●

Photocopy of Figure 3-5

●

Scissors

●

Matchstick

This is a dead-easy and quick sundial for you to

●

Glue

build. Take a photocopy of Figure 3-5. If you want

Project 1: Build a Solar-Powered Clock! Figure 3-5 Template for our “solar-powered clock.”

20

Project 1: Build a Solar-Powered Clock!

north or south. You will need to fold the sidepieces at

the same angle marked in degrees as your latitude.

Online resources

Stick a matchstick through the point at which all

of the lines cross. What you should be left with is

Sundials are absolutely fascinating, and a cheap

a piece of cardboard which makes an angle to the

way to investigate the properties of the sun. The

horizontal.

dial presented here is just one type of sundial;

however, there is a lot more information out there,

Now take your sundial outside and point the

a lot more to explore—here are some links, some

matchstick in the direction of due north (or south).

of them with printable plans that allow you to

You should be able to read the time off of the

make different types of sundial that you might

dial—compare this to the time on an accurate

like to investigate!

watch—remember you might have to add or take

www.nmm.ac.uk/server/show/

away an hour!

conWebDoc.353

www.liverpoolmuseums.org.uk/nof/sun/#

plus.maths.org/issue11/features/sundials/

Rules for solar positioning

www.hps.cam.ac.uk/starry/sundials.html

It is an artist’s rule that you look more than you

www.sundials.co.uk/projects.htm

paint—for solar positioning this is also true. You

www.digitalsundial.com/product.html

need to look carefully and make observations in

This page is well worth checking out . . . very

order to understand your site. Look at how objects

ingenious this is a “digital sundial,” yes you

on your plots cast shadows. See where your house

read correctly—a digital sundial.

overshadows and where it doesn’t at various times

of the year—remember seasonal variation—the

to be really flashy you can stick it to a piece of card-

position of the sun changes with the seasons and

board in order to make it more rigid and durable.

won’t stay the same all year round (Figure 3-6).

You need to cut out the dial that relates to the

Also, just because an area is shaded in one

hemisphere that you are in—north or south. Then,

season, doesn’t necessarily mean that it is shaded

you need to think about your latitude in degrees

in all seasons. In fact, this can often be used to

Figure 3-6

How seasonal variation affects the optimal position of solar collectors.

21

your advantage. For example, in summer, you

Think about when in the day you will be using

don’t want too much solar gain in your house as it

your solar device. Is it a photovoltaic cell that you

might overheat; however, in winter that extra solar

would like to be using for charging batteries all

energy might be advantageous!

day. Or, is it a solar cooker that you will be using

Think carefully about trees—if they are deciduous,

in the afternoon? Think about when you want to

they will be covered with a heavy veil of leaves in

use it, and what sunlight is available in what areas

the summer; however, they will be bare in the winter.

of your plot.

Trees can be used a bit like your own automatic

Work out which direction is north—try and find

sunshade—in summer their covering of leaves blocks

“true north” not just magnetic north. A compass will

the sun; however, in the winter when they are bare

veer toward magnetic north so you need to find a

they block less sun.

way of compensating for this. Having a knowledge

Make a record of your observations—drawings

of where north and south is can be essential when

are great to refer back to. Keep a notebook where

positioning solar devices. Note which walls face

you can write any interesting information about

which cardinal directions (compass points). If you

what areas are and aren’t in shadow. Note any-

are in the northern hemisphere, site elements where

thing interesting, and the time of day and date.

coolness is required to the north, and elements where

heat is required to the south.

Make sure that you are on the lookout on the

longest and shortest days of the year—the first day

Think about the qualities of morning sun and

of summer and the first day of winter. This is

evening sun. Position elements that require cool

because they represent the extremes of what your

morning sun to the east—and those elements which

solar observations will be; therefore, they are

require the hot afternoon sun to the west.

particularly useful to you!

Project 2: Build Your Own Heliodon

●

Countersunk screws to suit hinge

You will need

●

Lazy Susan swivel bearing

For the cardboard heliodon

For both heliodons, you will need

●

Three rigid sheets of corrugated cardboard,

2 ft × 2 ft (60 cm × 60 cm)

●

Clip on spotlamp

●

Packing tape

●

Length of dowel

●

Split leg paper fastener

●

Large blob of plasticine/modeling clay

For the wooden heliodon

Tools

●

Three sheets of 1/2 in. (12 mm) MDF or plywood

For the cardboard heliodon

2 ft × 2 ft (60 cm × 60 cm)

●

Length of piano hinge 2 ft (60 cm)

●

Scissors

Project 2: Build Your Own Heliodon

22

Project 2: Build Your Own Heliodon

●

Craft knife

wear out over time. This does not mean that there

●

Protractor

is any reason for it to be less rigid than its sturdier

wooden equivalent. The second design is for a

more rigid permanent fixture which can be used

For the wooden heliodon

professionally, for example if you are a professional

●

Bandsaw

who will routinely be performing architectural

design or using the heliodon for education.

●

Pillar drill

Our heliodon will consist of three pieces of board.

●

Sander

The first forms a base; on top of this base, we affix

●

Protractor

a second board which is allowed to swivel by way

We have already seen in this chapter about the

of, in the wooden version, a “Lazy Susan” bearing.

sun’s path—and we have learnt how we can use

This is a ball-bearing race that you can buy from a

the sun to provide natural lighting and heating.

hardware shop, which is ordinarily used as a table

We saw in Figure 3-3 how the position of the sun

for a “Lazy Susan” rotating tray.

and the earth influences the seasons, and how the

In the cardboard version, we simply use a split

path of the sun in the sky changes with the seasons.

leg pin pushed through the center of both sheets,

This is important to us if we want to design optimal

with the legs splayed and taped down.

solar configurations, as in order to maximize solar

The third board is hinged so that the angle it

gain, we need to know where the sun is shining!

makes with the horizontal can be controlled, it is

A heliodon is a device that allows us to look at

also equipped with a stay to allow it to be set at the

the interaction of the light coming from the sun,

angle permanently and rigidly. And that is just

and any point on the earth’s surface. It allows us to

about it! With the wooden version, a length of

easily model the angle at which the light from the

piano hinge accomplishes this job admirably, and

sun will hit a building, and hence see the angle

with the cardboard version, a simple hinge can be

cast by shadows, and gauge the paths of light into

made using some strong tape.

the building.

The other part of the heliodon is an adjustable

The heliodon is a very useful tool to give us a

light source. This can be made in a number of

quick reckoning as to the direction of light coming

ways. The simplest of which is a small spotlamp

into the room, and what surfaces in that room will be

equipped with a clip that allows it to be clamped to

illuminated at that time and date with that orientation.

a vertical object such as the edge of a door. Slide

A heliodon is also very useful for looking at

projectors are very good at providing a parallel

overshadowing—seeing if objects will be “in the

light source—these present another option if their

way” of the sun.

height can easily be adjusted. If you will be using

With our heliodon, it is possible to construct

the heliodon a lot, it would make sense to get a

scale models that allow us to see, for example, if a

length of wood mounted vertically to a base, with

certain tree will overshadow our solar panels. The

the dimensions given in Table 3-1 marked

heliodon is therefore a very useful tool for solar

permanently on the wood.

design, without having to perform calculations.

In this project, we present two separate designs.

The first is for a cardboard heliodon, which is

Heliodon experiments

simple if you just wish to experiment a little with

how the heliodon works. The design requires few

Once you have constructed your heliodon you can

materials and only a pair of scissors—but, it may

begin to perform some experiments using it.

23

Table 3-1

Lamp heights for different months of the year

January 21

8 in.

20 cm

from floor

February 21

22 in.

55 cm

from floor

March 21

40 in.

100 cm

from floor

April 21

58 in.

145 cm

from floor

May 21

72 in.

195 cm

from floor

June 21

80 in.

200 cm

from floor

July 21

72 in.

195 cm

from floor

August 21

58 in.

145 cm

from floor

September 21

40 in.

100 cm

from floor

October 21

22 in.

55 cm

from floor

November 21

8 in.

20 cm

from floor

December 21

2 in.

5 cm

from floor

Figure 3-7

Heliodon table adjustments.

These measurements are assuming a measurement of 87 in. between

the center of the heliodon table and the light source

You need to be aware of the three main

Compass points

adjustments that can be made on the heliodon.

Remember to think carefully about where north

●

Seasonal adjustment—by moving the lamp up and

and south are in relation to your modeling table.

down using the measurements listed above, it is

Consider whether the site you are modeling is in

possible to simulate the time of year.

the north or south hemisphere and adjust the

●

Latitude adjustment—by setting the angle that the

position of your model accordingly.

uppermost flat sheet makes with the base, you can

adjust the heliodon for the latitude of your site.

●

Time of day adjustment—by rotating the assembly,

this approach to calibrate your heliodon. You might

you can simulate the earth’s rotation on its axis,

like to make some marks on the cardboard surface

and simulate different times of day.

to indicate different times of day.

The two table adjustments are illustrated in

The next stage of experimentation with the

Figure 3-7.

heliodon is to look at modeling a real building.

In order to secure the table at an angle, probably

the easiest way is to use a length of dowel rod with

a couple of big lumps of modeling clay at each

end. Set the angle of the table to the horizontal,

then use the dowel as a prop with the plasticine to

secure and prevent movement.

There are a couple of simple experiments that

we can do with our heliodon to get you started.

Remember the sundial that you made earlier in the

book? Well, set the angle of latitude on your table

to the angle that you constructed your sundial for

(Figure 3-8). You will see that as you rotate the

Project 2: Build Your Own Heliodon table, the time on the sundial changes. You can use Figure 3-8

Heliodon sundial experiment.

24

Project 3: Experimenting with Light Rays and Power

Online resources

Read more about heliodons on the web

www.pge.com/003_save_energy/

003c_edu_train/pec/toolbox/arch/heliodon/

heliodon.shtml

arch.ced.berkeley.edu/resources/bldgsci/

bsl/heliodon.html

en.wikipedia.org/wiki/Heliodon

Figure 3-9

Using a cardboard model building to

model solar shading.

Construct a model from cardboard (Figure 3-9),

the year. Use the heliodon with scale models to

and include for example, window openings, doors,

devise your own solar experiments!

patio doors, and skylights. By turning the table

Now with modern computer aided design (CAD)

through a revolution, it is possible to see where

technology, the heliodon can be replicated digitally

the sun is penetrating the building, and what parts

inside a computer. Architects routinely use pieces

of the room it is shining on. This is useful, as it

of CAD software to look at how light will

allows us to position elements of thermal mass in

penetrate their buildings, or whether obstructions

the positions where they will receive the most solar

will overshadow their solar collectors. However,

radiation.

heliodons are still a very quick, simple technology

We can also make models of say, a solar array,

which can be used to make a quick appraisal of

and cluster of trees, and see how the trees might

solar factors on a model building. A professional,

overshadow the solar array at certain times during

more durable heliodon can be seen in Figure 3-10.

Project 3: Experimenting with Light Rays and Power

You will need

one end roughly to the center of the paper with the

tape. Now hold the string to one side of the piece

of paper, and attach the torch to the string so that

●

Small torch

the bulb of the torch falls within the boundary of

●

Length of string

the paper.

●

Tape

We are going to see how angle affects the light

●

Big sheet of paper

power falling on a surface when the distance from

●

Bunch of pencils

the surface remains the same.

●

Elastic band

Now imagine our torch as the sun, hold the

Attach the large sheet of paper to the wall using

torch to face the paper directly keeping the string

the tape. Then, take the piece of string, and attach

taught. You should see a “spot” of light on the paper.

25

However, the area on which the light fell did

change. When the torch was held perpendicular

to the paper, there was a circle in the middle of

the page. However, hold the torch at an angle to

the page and the circle turns into an oval—with the

result that the area increases. What does this mean

to us as budding solar energy scientists? Well, the

sun gives out a fixed amount of light; however, as

it moves through the sky, the plane of our solar

collectors changes in relation to the position of the

sun. When the sun is directly overhead of a flat

plate, the plate receives maximum energy; however,

as we tilt the plate away from facing the sun directly,

the solar energy reaching the plate decreases.

You might have noticed that as you angled the

torch and the beam spread out more, the beam also

became dimmer.

Remember the bunch of pencils? Well grab them

and put an elastic band around them. Imagine each

pencil is a ray of light from the sun. Point them

Figure 3-10

A professional architect using a heliodon

down and make a mark with the leads on a piece

to make estimations of solar gain on a model building.

of paper. Now, carefully tilt all the pencils in rela-

tion to the paper and make another mark with

Draw a ring around the area of highest light intensity.

all the pencils at the same time (Figure 3-12).

Now, hold the torch at an angle to the paper, and

As you can see, the marks are more spread out.

again with the string taught, draw a ring around the

Remembering that we are equating our pencil

area of high intensity. Repeat this at both sides of

marks with “solar rays,” we can see that when a

center a few times at different angles.

given beam of light hits a flat surface, if the beam

Figure 3-11 shows us what your sheet of paper

hits at an oblique angle, the “rays” are more spread

might look like.

out. This means that the power of the beam is

being spread out over a larger area.

What can we learn from this? Well, the power of

It is important that we understand how to make

our torch remained the same, the bulb and batteries

the most of the solar resource in order to make our

were the same throughout the experiment, the amount

solar devices as efficient as possible.

of light coming out of the torch did not change.

Figure 3-11

Light ray patterns drawn on paper.

Figure 3-12

Bunch of pencils experiment.

Project 3: Experimenting with Light Rays and Power

26

Chapter 4

Solar Heating

The sun provides us with heat and light that is

Consumption of fossil fuels for heating is tremendous

essential to life all year round.

when you consider the global scale. Producing as

One of the most efficient ways of harnessing the

much as possible of our heat from renewable

sun’s energy is to use it to space heat our build-

resources will considerably reduce our consumption

ings, and produce hot water for our daily needs,

of fossil fuels.

such as washing, cleaning, and cooking.

When you think about the truly tremendous

amount of heat that the sun produces, it seems

Can I use my roof

absolutely ridiculous that we should want to burn

our precious fossil fuels to heat things up.

to mount my solar

We can use the sun to directly heat our buildings—

heating panels?

this is known as passive heating—or we can use an

intermediate storage and distribution medium such

The roof seems an obvious place to want to mount

as water or air. The advantage of using water or air

your solar heating panels. After all, you have a large

as a storage medium for the heat, is that we can

area which is currently unutilized just waiting for

concentrate the sun, and collect it efficiently using

some clean green energy generation!

solar collectors, and then using a distribution network

First of all, you should consider the structural

of pipes or ducts, we can direct the heat to where

integrity of your roof and how strong it is.

we want it; and, more importantly, direct the heat to

Remember, the roof will not only need to support

the places where it can be utilized most effectively.

the weight of the solar heating panel and all of the

In this chapter, we are going to be looking at the

associated paraphernalia, but might also need to

fundamentals of a solar hot water heating system.

support your weight as you install it.

By the end of the chapter, you should have an

You will also need to consider the orientation

understanding of how such systems work, and be

of your roof and whether it is positioned in such

armed with the knowledge to begin researching

a manner that it will receive optimal solar gain.

and installing your own hot water system.

If you are in the northern hemisphere, you will

want a roof which faces as near to due south as

possible. If your roof does not face directly due

south, there will be some loss of efficiency—which

Why use solar energy

is proportional to the angle of deviation from due

for heating?

south.

If you live in the southern hemisphere, the

There are considerable environmental benefits

reverse is true—you want a roof that faces due

associated with using renewable energy for heating.

north in order to catch the best of the sun’s rays.

27

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

shading and brie soleil to ensure that the room

How does solar

receives an optimal amount of light in both

summer and winter. Passive solar design is a whole

heating work?

book in its own right though!

On a hot summer day, if you are walking around a

parking lot, gently touch a black car, and the chances

What does a solar

are it will feel very hot. Now touch a silver or white

car, and you will find that it is significantly cooler.

heating system

This is the principle that underpins solar heating.

look like?

A black surface heats up quickly in the sun.

Our demand for hot water is driven by a number

Figure 4-1 illustrates a basic solar water heating

of things. We use hot water every day for tasks such

system.

as washing our hands, clothes and dishes. From now

We can see a large storage tank in the Figure.

on, we will refer to this as “solar hot water.” We can

This is filled with water and is used as a thermal

also use hot water for heating our homes. We will

store. It is imperative that this tank is incredibly

refer to this as “solar space heating” from now on.

well insulated as it is pointless going to a lot of

What we need to do, is look at our demand for

effort to collect this solar energy if we then lose it

heated water, and see how it correlates to the

in storage!

energy available from the sun.

You will notice that the solar hot water tank has

a gradient fill—this denotes the stratification of the

water—the colder water sinks to the bottom, while

the warmer water is at the top of the tank.

Solar hot water

We draw the hot water off from the top of the

Our demand for hot water is fairly constant

tank, while replacing the hot water with cold water

throughout the year. We use more or less the same

at the bottom of the tank. This allows us to maintain

amount of hot water for washing and cleaning in

the “layered” stratified nature of the tank.

the winter as we do in the summer.

At the bottom of the tank, we can see a coil; this

is shown more clearly in Figure 4-2—this coil is in

fact a copper pipe—we can see that the pipe enters

the tank at the bottom, and exits the tank at the top.

Solar space heating

The pipes are connected in a closed circuit to a

solar collector. This closed circuit is filled with a

We can also use solar energy to heat our space

fluid which transfers the heat from the solar cell to

directly—passively, rather than using an active

the tank.

system. This is called passive solar design. We can

design our buildings with large expanses of glass

This is the simplest type of solar system—it is

on the sun-facing façades in order to capture the

called a thermosiphon. The reason for this name is

solar energy and keep the building warm and light.

that the process of circulation from the solar cell to

However, the requirements for space heating are

the tank is driven by nothing more than heat. Natural

different in the winter from in the summer. If we

convective currents set up a flow, whereby the hot

design our buildings for “summer conditions,” they

water makes its way around the circuit.

could be intolerably cold in the winter. For this

It is also possible to insert a pump into this circuit

Solar Heating reason, we can use architectural devices such as to increase the flow of the heat transfer medium.

28

Solar Heating

Figure 4-1

A basic solar water heating system.

We can also drive this pump using photovoltaic

solar cells. This means that our heating is not using

electricity from the grid—and hence not using

energy generated from fossil fuel sources. There is

one manufacturer, Solartwin, which supplies a

system which consists of a solar thermal panel, and

a pump driven by photovoltaics. The advantage of

this approach is that the energy for the pump is

provided at the same time as there is heat in the

system.

Tip

A good science fair project might be to build a

demonstration solar water heating system using

easy-to-use flexible aquarium tube for the

“plumbing” and a soda bottle for the hot water

storage tank. A few thermocouples or thermistors

will allow you to monitor the temperatures around

the setup and see how effectively it is working.

Figure 4-2

A cutaway of a thermal store tank.

29

Figure 4-3

Flat plate versus evacuated tube collectors.

Solar collectors

There are two types of solar collector: flat plate,

and evacuated tube. We can see in Figure 4-3

the two types of collectors compared. While a

greater amount of sun falls on the flat plate, the

evacuated tube collectors are better insulated.

However, as the sun moves in an arc through the

sky, the flat plate collector’s effective area becomes

smaller, and as the evacuated tube collectors are

cylindrical, the area presented toward the sun is

the same.

Figure 4-4

Cutaway of a flat plate collector.

In Figure 4-4 we see the make up of a flat plate

collector. It is essentially quite a simple device.

There is insulation, which stops the heat that it

This could simply be matt black, or it could be a

absorbs from being transmitted into the roof it is

selective coating.

mounted on. A coil of tube within this collects the

On the roof shown in Figure 4-5 we can see a

heat and transmits it to the storage tank, and at the

variety of different solar cells, both thermal and

Solar Heating front of the collector is an absorbent surface.

photovoltaic nestling together in harmony.

30

Project 4: Build Your Own Flat Plate Collector

Figure 4-5

An array of different solar thermal cells on a roof.

Project 4: Build Your Own Flat Plate Collector

We are now going to make a flat plate collector.

The key thing to remember about solar collectors

There are a number of different types of collector,

is keeping the heat in and the cold out. This can be

all suitable for relatively simple manufacture in a

accomplished by using glazing on the sun-facing

home workshop (Figures 4-6 to 4-8).

side of the panels and thermal insulation on the side

Figure 4-6

A commercially made clip fin collector.

31

Aluminum clip fins are one of the easiest ways

of assembling a solar collector quickly, as they

essentially clip onto a matrix of copper pipe.

Another way of constructing a solar collector is to

use an old radiator painted black inside an insulated

box—crude but effective! (Figure 4-9). This system

contains more water, and as a result has a slower

response time. This is because it takes more time to

heat up the thermal mass of the radiator.

Warning

One of the problems that solar collectors suffer

from is freezing in the winter. When temperatures

Figure 4-7

A home-made clip fin collector.

drop too low, the water in the pipes of the

collectors expands—this runs the risk of severely

that faces away from the sun. We need to try to

damaging the collectors.

eliminate thermal bridges as far as we possibly can.

Figure 4-8

Aluminum clip fins.

Project 4: Build Your Own Flat Plate Collector

32

Project 5: Solar Heat Your Swimming Pool

Figure 4-9

A recycled radiator collector.

Project 5: Solar Heat Your Swimming Pool

While having a pool in your yard is a great way to

are throwing into your pool is being lost as it

exercise and enjoy the summer sun, swimming

dissipates into the atmosphere. This isn’t smart!

pools are notorious for “drinking” energy.

Building some kind of enclosure over your pool

The problem is that there is simply such a great

will make the most of any investment that you put

volume of water to heat!

into solar heating your pool.

Energy is becoming more expensive as we begin

Once you have taken steps to minimize the

to realize the serious limitations of the previously

energy that your pool requires, you can begin to

cheap and abundant fossil fuels.

make advances toward heating it using free solar

Some people heat their pools in order to be able

energy. There is nothing really too complicated

to enjoy them out of season; however, that comes

about a solar pool heating system. As we only need

with a big associated energy cost.

to elevate the temperature of the water slightly, we

can use simple unglazed reflectors.

Before you even start to consider heating your

pool using solar energy, you need to consider

The reason? Well think of it like this . . . the

energy reduction and efficiency measures. You

water you get from the hot tap to wash with is

might want to consider your usage patterns. Will it

significantly hotter than the sort of temperature

really make much difference to me if I can’t use

you would be expecting to swim in. A domestic

my pool out of season? After all, who really wants

solar hot water rig heats a small volume of water

to swim when it is cold and wet outside! Also you

to a very high temperature. By contrast, a solar

might want to consider energy minimization

pool heating system, takes a large quantity of

strategies. Is your pool outside and uncovered at

water, and heats it by a small amount. Here is the

the moment? Heat rises . . . so all that heat that you

fundamental difference. Because the water is

33

circulating at a faster rate, unglazed collectors can

The Supplier’s Index (Appendix B) lists a

provide acceptable efficiency.

number of companies that sell products for solar

But that’s not all!

heating your pool.

In some hot climates, pools can have a tendency

to overheat. Solar collectors can save the day here!

By pumping water through the collectors at night it

Do we need to use solar

is possible to dump excess heat.

This technology isn’t just applicable to small pools

thermal power directly?

at home, large municipal pools are also heated by

solar technology in a number of cases. Take for

If we consider power generation on a large scale,

instance the International Swim Center at Santa Clara,

all of our power stations whether they be nuclear,

California, 13,000 square meters of solar collector

coal, oil, or gas fired, all produce heat primarily,

heat a total of 1.2 million gallons of water a day!

and then use this heat to produce steam, which

then, through using rotating turbines, produces

Figure 4-10 illustrates solar pool heating.

electricity.

This means, that at present, we do not produce

Tip

electricity directly from chemicals, like we do in a

battery—we first produce heat as an intermediate

process, which is in turn used to produce electricity.

Enerpool is a free program that can be used to

simulate your swimming pool being heated with

Once we recognize this, we quickly realize that

solar collectors. By inputting information such as

it could be possible to use solar thermal energy to

your location, and how the pool is covered. The

raise steam to generate electricity.

program can predict what temperature your pool

will be at, at any given time!

And this is exactly what they are doing in

Kramer Junction, California.

www.powermat.com/enerpool.html

Project 5: Solar Heat Your Swimming Pool Figure 4-10 Solar pool heating.

34

Project 6: Useful Circuits for Solar Heating

Figure 4-11

Solar thermal power in the Mojave desert. Courtesy Department of Energy.

Project 6: Useful Circuits for Solar Heating

Although we have discussed basic systems

●

100 k variable resistor

here for producing solar heat—and by no means

●

741 op amp

is this comprehensive coverage of solar heating

●

1 M resistor

(the subject really deserves several books in its

●

4.7 k resistor

own right) there are a number of things that we

can do to improve our system. If our system is

●

BC109 NPN transistor

“active,” which is to say if there is a pump

●

6 V piezo buzzer

driving a working fluid around the system,

●

Heatshrink tubing

then we can do a little more to control the

●

Mastic/silicone sealant

fluid.

If our system is passive, i.e., a thermosiphoning

Optional

system, where the fluid makes its way around the

system as a result of changes in density, then we

●

6 V relay

might at least like some feedback as to what our

●

Protection diode

system is doing.

Tools

You will need

●

Soldering iron

●

Negative temperature coefficient thermistor

●

Side cutters

●

2 × 10 k resistor

●

Solder

35

Figure 4-12

Solar heating over temperature indicator.

The following is a simple circuit that uses a

thermistor as the sensing element to provide

Protecting the sensor

feedback as to the condition of a surface being

against the elements

monitored. There are two simple circuits here—

both are similar with one small change—the

A thermistor as supplied from the components

position of the thermistor and variable resistor

shop is a pretty fragile beast, and as such should

which change places (Figures 4-12 and 4-13).

be respected if reliable operation is wanted.

Project 6: Useful Circuits for Solar Heating Figure 4-13 Solar heating under temperature indicator.

36

Project 6: Useful Circuits for Solar Heating

The device is designed to be soldered onto a

Modifications to the circuit

printed circuit board; however, we are expecting it

to be used in a much more hostile environment.

Although the circuit is useful in its own right, there

For this reason, provision should be made to

are a couple of things that we can do to improve its

insulate the leads of the thermistor with some

functionality. As it stands, the circuit provides an

heatshrink tubing, which will provide mechanical

“alert” when the temperature goes out of condition;

support for the soldered joint, and also prevent

however, we might consider a scenario where we

ingress of water.

are not at home to take action. In this instance, we

Once each individual lead has been insulated,

might want to replace the piezo buzzer in the system

the pair can be bound together with a little more

with a relay and protection diode. This is a straight

heatshrink, or failing that a little bit of tape. The

swap, and allows the circuit to then control an

sensor should be provided with long enough leads

automatic device which can take action—for

to comfortably reach the circuit board. If your

example a pump or electronic valve.

solar collector tracks the sun, you will need to

To give you an example of how this circuit

ensure that the leads are sufficiently long to reach

could be useful in your solar water heating

back to the circuit board, even at the extent of your

system, in freezing weather, if no water is

collector’s movement.

circulating in the pipes, there is a risk that that

Taking this a step further, you need to mate

water could expand and burst your pipes. To

your sensor to the surface being monitored. A

overcome this, a relay could switch on a trickle

little squeeze of heat transfer compound in the gap

pump which keeps a little water circulating

between thermistor and the surface is not a bad

through the pipes. This water will carry with it

idea—you can get this from computer suppliers, as

some heat from the thermal store, which should

it is commonly used to ensure a good surface

keep your pipes free of ice.

interaction between a CPU and heatsink.

Equally, with the resistors reversed as in the

Once you have done this, you can apply silicone

second circuit, you might want to set up a system

sealant liberally to hold the sensor in place. If you

whereby a pump is triggered when heat in the

really want to go the whole hog, you can even insu-

collector is sensed. This ensures that hot water

late the other side of the sensor with a little thermal

isn’t pumped through a cold collector.

lagging, such as polystyrene or a slice of foam pipe

lagging. This will prevent the sensor from being

unduly influenced by external fluctuations in

What is the future

temperature.

of solar heating?

It is inevitable that in the future, we will need to

Calibrating the sensor

seek different solutions to our problems as we are

forced not to depend on fossil fuels. Solar energy

When setting the circuit up, you will need to calibrate

certainly has a place in meeting our heating needs

the sensor against a reference of known temperature.

in the future, and considering the energy from the

A water bath is a good way of providing a stable

sun is free, it is very surprising that more people

temperature. To get the temperature you desire, get a

aren’t using it now!

cup of ice water and a cup of boiling water, and use

these to adjust the temperature of a cup of water with

We have seen in this chapter how solar heating

a thermometer immersed in it.

can meet our heating needs, but that the availability

37

of solar energy is seasonal, and in part that deter-

but maybe solar energy has another trick up its

mines the supply of solar hot water.

sleeve—biomass!

Even when the sun cannot provide all of the

The trees and plants that we are surrounded by

energy all of the time, or where 100% solar

are effectively solar batteries! They take the energy

provision would be uneconomical, it can certainly

produced from the sun, and using a process called

go a long way toward reducing the amount of energy

photosynthesis, use the energy to grow. All the time

we need to consume. Even pre-heating water a little

that they are growing, they are taking in carbon

bit in winter goes some way to saving energy.

dioxide from the atmosphere and producing oxygen.

Another thing that needs careful consideration,

Once a tree has grown, we can cut it down and burn

is that if we need to provide extra energy for our

it. While this process releases carbon dioxide into

heating needs, where will that energy come from?

the atmosphere, there is no “net gain” of carbon

Fossil fuels pollute the atmosphere and are a finite

dioxide, as the tree took the carbon dioxide out of

resource, nuclear leaves a legacy of toxic waste,

the atmosphere while growing!

The Future of Solar Heating

38

Chapter 5

Solar Cooling

In hot climates, it can often become uncomfortably

hot—in the modern world, we tend to look toward

Passive solar cooling

air conditioning to provide a comfortable internal

atmosphere; however, air conditioning often leaves

There are a number of ways that we can design our

us with dry stale air.

buildings to stay at a pleasant internal temperature,

While it would seem to be counterintuitive to

and prevent them from overheating, even in the

use the sun to cool things down, there are a

summer.

number of techniques that we can use to cool

things down by employing the sun’s energy.

Trombe walls

As with many of the themes in this book, this idea

is not a new one, in fact it was patented in 1881

Why air conditioning

(U.S. Patent 246626). However, the idea never

is bad

really gained much of a following until 1964,

when the engineer Felix Trombe and architect

The amount of energy that air conditioning consumes

Jacques Michel began to adopt the idea in their

is truly tremendous. In addition to this, the heat

buildings. As such, this type of design is largely

extracted from the building is simply dumped out

referred to as a “Trombe wall.”

into the atmosphere. Air conditioning cooling

Figure 5-1 shows a Trombe wall on one of the

stacks are a breeding ground for Legionella bacteria,

resident’s houses at the Centre for Alternative

and the refrigerants used in air conditioning are

Technology (CAT), U.K.

ozone-depleting and add to the burden of global

Let’s describe the construction and operation of

warming. While there has been a worldwide move

the Trombe wall.

to eliminate CFCs from air conditioning units

Essentially, the Trombe wall is a wall with a

because of the damage they do, the interim HCFC

high thermal mass, the wall is painted black to

and HFC chemicals are still not environmentally

enable it to absorb solar radiation effectively.

friendly.

The wall is also separated from the outer skin of

glazing by an air gap.

The original Trombe walls were not particularly

effective. They worked by absorbing heat in the

What can we

thermal mass during the day. At night, this heat

do instead?

would be dissipated both into the room—but also

to the outside through the air gap and glazing. The

Rather than using large amounts of fossil fuels,

theory was that the glazing would help to retain

there are a number of other strategies that we can

heat, and because the thermal mass had gained

use to cool our buildings.

enough heat during the day, it would be warmer

39

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

will know that as air heats up, the molecules of

gas gain a little more energy—this causes them

to bounce around a bit more, and as a result, they

tend to spread out a little bit. As they do this, the

body of gas becomes less dense. As you will

know if you have ever observed a spill of oil on

a body of water, the less-dense compound floats

to the surface as it is displaced by the more-dense

compound. In this case, the lighter air rises up

through the gap between the wall and the glazing.

This is the principle that hot air balloons use to

operate—hot less-dense air floats above denser

air!

This convective current can be used to either

heat or cool the building.

Remember those gaps in the wall and glazing—

well, if both of the vents in the wall (the thermal

mass side of things) are opened, air will be sucked

out of the room at the bottom, heated as it contacts

the thermal mass, and using convection will rise up

to the top of the air gap, where it flows back into

Figure 5-1

Trombe wall at CAT, U.K.

the room.

Of course during the summer, this heat isn’t

than the internal room temperature, as a result, the

really wanted—so the flaps can simply be closed

room would warm up.

in order to keep the room cool.

In reality it appeared that most of the heat was

But this chapter did say it was about solar

simply dumped to the cold outside.

cooling!

A series of improvements were made to the

Well, if you also have flaps in the glazing which

design of the Trombe wall which significantly

can be opened and closed, you can then open a

increased its performance. In the improved version

flap at the top of the glazing, and at the bottom of

of the Trombe wall, there are vents at the top and

the thermal mass. The flap at the top of the thermal

bottom of the wall, and also on the glazing.

mass is closed.

These vents have a mechanism that allows them

This sets up a convective current which sucks air

to be opened and closed in certain configurations.

out of the bottom of the room, and heats it slightly,

The general scheme of things is that the sun

causing it to rise. But rather than this air being fed

shines through the glazing, where it heats up the

back into the room, the air is instead dissipated

thermal mass of the wall behind. The wall, being

into the outside atmosphere. This has the effect of

of a construction that has a high thermal mass (for

sucking air from the room. This air has to be

example masonry or concrete) transfers some of

replaced somehow, so what happens is that fresh

the heat energy to the air in the gap between the

air is sucked in through cracks in the building

glazing and the wall as it heats up.

fabric, gaps in doors and windows, etc. This pro-

A convection current is set up. If you are

vides a fresh cooling breeze for the occupants

Solar Cooling familiar with heat and the way it affects air, you (Figure 5-2).

40

Solar Cooling

Figure 5-2

Trombe wall modes of operation.

conditioning which is thirsty for electricity. Of

Passive evaporative techniques

course, as we have seen, we can easily generate

heat using solar methods.

When water evaporates, it takes with it energy.

To understand how solar cooling differs from

We can exploit this phenomenon to cool buildings.

conventional refrigeration methods, let’s compare

These techniques all require water, which might

the two and look at similarities and differences.

not be possible in some hotter countries where

water availability is limited. Also, it must not be

In a conventional refrigeration setup,

forgotten that there is a requirement for energy to

a refrigerant—a substance that readily evaporates at

pump the water to the top of the building. This

a low temperature—is compressed, which causes it

energy must be provided in a sustainable manner.

to become liquid. This compression is usually

driven by an electric motor—using valuable watts

in the process. The refrigerant is then allowed to

Roof sprays

expand—to do this it requires heat, which it gains

from the material under refrigeration. As the heat

Spraying the roof with a fine mist of water is one

transfers from the material to be refrigerated to the

way to keep the roof wet and permit evaporative

refrigerant, the refrigerant expands. It must then be

cooling. The roof must be suitably coated to

compressed and forced around the loop again! This

prevent water ingress, which could damage the

cycle continues indefinitely—no refrigerant should

fabric of the building.

escape from the system.

Our system works in a slightly different way.

Roof ponds

The refrigerant is kept “locked up” in a material

which soaks up refrigerant like a sponge soaks up

A roof pond is one way of providing a large body

water. As we heat this material, the refrigerant is

of water which can be evaporated, taking heat with

liberated from it, turning into a liquid as it con-

it as it leaves the roof.

denses. This liquid will readily evaporate again—it

is encouraged to do this by the absorbent material

which tries to “suck” the refrigerant back once it

Active solar cooling

has cooled. As the refrigerant shuttles back to the

absorbent material it takes heat with it. This shut-

Active solar cooling is a little bit more involved

tling back and forth continues—so the process

than passive solar cooling. In active solar cooling,

is a bit more like a train going back and forth in

we use a thermally driven process of some sort in

a straight line, than a train continually circling in

order to cool our buildings, rather than air

a loop.

41

Project 7: Solar-Powered Ice-Maker

I am grateful to Jaroslav Vanek, Mark “Moth” Green

refrigerant—however, they tend to use water as the

and Steven Vanek for the information on how to make

absorbing medium.

a solar-powered ice-maker. This design was originally

published in Home Power magazine, Issue no. 53.

Construction and assembly

The original article can be downloaded from the

The first item to be assembled is the solar collector

Home Power website at:

pipe. This is made from the length of black iron

homepower.com/files/solarice.pdf

pipe. First of all you should cut a foot off the end,

as we will need this for the ammonia storage tank.

The pipe should be capped at the ends with the

You will need

3 in. black caps, but before you do this, you need

to drill one of the caps to accept a 1/4 in. nipple and

●

Four sheets galvanized metal, 26 ga.

a coupling for the rest of the plumbing. The collector

●

3 in. black iron pipe, 21 ft length

can now be filled with the calcium chloride salt

which will act as the absorber. The caps can now be

●

120 sq ft mirror plastic

secured firmly in place. Whatever method you

●

21⁄4 in. stainless steel valves

choose, you should ensure that the joint is capable

●

Evaporator/tank (4 in. pipe)

of withstanding pressure—as when the ammonia is

●

Freezer box (free if scavenged)

produced it will be hot and anywhere near two

●

4 ft × 8 ft sheet 3/4 in. plywood

hundred pounds per square inch pressure.

●

six 2 × 4 timbers, 10 ft long

You next need to form a condenser coil and tank.

The tank is easy—take a standard 55 gallon drum,

●

Miscellaneous 1/4 in. plumbing

and slice it in half. This will give you a nice

●

Two 3 in. caps

container to pump full of water.

●

11⁄4 in. black iron pipe, 21 ft length

Now a word about gravity—there are no pumps

●

Four 78 in. long 11/2 in. angle iron supports

in this system to make the working fluid go up

●

15 lb ammonia

and down, so you need to think of other ways of

●

10 lb calcium chloride

doing this. Mount the condenser coil high up,

This design is for an ice-maker which will produce

above the level of the solar collector. Now have

about 10 lb of ice in a single cycle. It uses the

the pipe from the collector running to the top of

evaporation and condensation of ammonia as a

the coil in the tank. The pipe from the bottom

refrigerant. If you remember in the explanation

of the coil to the storage tank should be as straight

above, I mentioned that we needed a refrigerant

a run downhill as possible, try to eliminate any

and an absorber for this type of cooler to work.

bends or kinks if at all possible (Figures 5-3

Well, the ammonia is our refrigerant, and we use a

and 5-4).

salt—calcium chloride—as the absorber. You

In the collector made by Jaroslav Vanek, Mark

might have seen small gas fridges often used in

“Moth” Green and Steven Vanek, the steel pipe of

caravans and RVs which can be powered by

the collector was supported from the ground by

Project 7: Solar-Powered Ice-Maker propane—these also generally use ammonia as a two sturdy uprights. The solar collector was then

42

Project 7: Solar-Powered Ice-Maker

Figure 5-3

Solar cooler layout.

suspended from this using U bolts. This allowed

the collector to be moved to accommodate seasonal

How does the ice-maker work?

variations.

The ice-maker works on a cycle—during the

daytime ammonia is evaporated from the pipe at

Warning

the focal point of the parabolic mirrors. This is

because the sun shines on the collector which is

For the system to operate for long periods of

painted black to absorb the solar energy—this

time, the materials used should be resistant to

collector heats up, driving the ammonia from the

corrosion by ammonia. Steel and stainless steel

salt inside.

are ideal in this respect as both are immune to

At night, the salt cools and absorbs the

corrosion by ammonia. Another consideration is

ammonia, as it does this, it sucks it back through

the pressure under which the system will have to

the collector. As it evaporates from the storage

operate.

vessel, it takes heat with it.

Figure 5-4

Solar cooler plumbing details.

43

Figure 5-5

The solar cooler cycle.

Figure 5-5 illustrates this cycle.

Useful addresses

The following addresses may be useful if you wish to

Note

make further enquiries about this design of ice-maker:

S.T.E.V.E.N. Foundation,

This design has a number of strengths which

414 Triphammer Rd.

make it robust and reliable in operation. One of

Ithaca,

those strengths is that the design has an absolute

NY 14850

minimum of moving parts. The only things that

U.S.A.

actively move are the valves—and even these are

operated infrequently. The elimination of moving

SIFAT,

parts makes this design very efficient.

Route 1, Box D-14

Lineville,

AL 36266

U.S.A.

Project 7: Solar-Powered Ice-Maker

44

Chapter 6

Solar Cooking

sooner rather than later if everybody wants to live

Why cook using

a western lifestyle—but why even should we in the

West want to live a western lifestyle when things

the sun?

like solar cooking can be so much fun—and

achieve the same ends that conventional cooking

Solar cooking is a great alternative to conven-

does, heating a food product.

tional cooking—rather than burning fuel and

All of the projects in this chapter can be built

producing carbon dioxide emissions, or using

very cheaply and are ideal for a fun summer’s

precious electricity, solar cooking harnesses

day!

the natural energy available from the sun! It

is a great social activity on a sunny day—barbe-

At the end of this chapter, I have put together a

ques are just sooooo yesterday—solar cooking

collection of links to various different types of

is where it is at! No fumbling with matches

solar cooker plans that are out there on the web—

and firelighters, no choking on smoke, no

all have different strengths and weaknesses and

burnt sausages! Just hope that the clouds don’t

are suited to different applications, from designs

come!

that will just about cook a frankfurter, to large

cookers that can be used for community catering!

Although you won’t see any T.V. chefs preparing

meals on a solar cooker, it doesn’t mean that they

aren’t any good—it just means that T.V. chefs lack

technological imagination.

There are lots of different designs of solar

cooker all suited to different applications—all rely

on similar principles—concentrating the sun’s

energy into a small area and then trying to retain

the heat.

Solar cooking solutions are elegant in their

simplicity and as such are suited to developing

world applications (Figure 6-1). Many countries do

not have the developed infrastructure that we have

in the West for distributing energy. As a result, a

hot, cooked meal is hard to come by—as fuel may

be scarce.

Think of it like this—the developed world is

already using a massive amount of energy to cook

food—with large nations like India and China

Figure 6-1

A solar cooker being used in the

growing and developing, our energy will run out

developing world. Image courtesy Tom Sponheim.

45

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Project 8: Build a Solar Hot Dog Cooker

Here we have a couple of options, the “quality-

You will need

built-to-last” option, and the “cheapskate” option.

The quality-built-to-last option involves buying

●

Small photovoltaic cell

some flexible acrylic mirror from the internet. This

●

Solar motor

is often seen on auction sites in large panels as

●

Plywood

people use it for interior design, and can sometimes

●

Framing

be found in garden supply stores as people put it at

strategic locations in their garden in order for it to

●

Screws

appear bigger.

●

Flexible acrylic mirror

The acrylic mirror can be bent gently without fear

●

Elastic band and pulley wheel

of breaking, and also has the advantage that it can be

or

drilled relatively easily without fear of splintering.

●

Small plastic worm gear and large plastic

If you are opting for the cheap option, you can

gear to match

get away with using some corrugated cardboard,

covered in glue, followed by tin foil. Note that your

Tools

collector efficiency will not be as good, as the sur-

face is not as reflective. However, for a demonstra-

●

Bandsaw

tion it works to a degree.

●

Drill

Next, you need to construct a support for the

●

Router

mirror—if you are building to last then use

plywood and framing. A router might be useful to

machine a groove which will support the mirror,

This list of components is for the deluxe

if you are making the cheaper cardboard version, you

version—the automatic hot dog turner is a cool

just need to cut some flaps to support the “mirror.”

novelty, but not essential as it is just as easy to

Now we come to the drive mechanism. We have

turn by hand! If you want to make a simpler

a couple of options here (Figures 6-2 and 6-3). You

cheaper version, substitute the plywood for card,

can just provide a simple support for a skewer and

the plastic mirror for tin foil, and rather than have

turn your hot dog by hand.

a motor turn your hot dog on a skewer, just

provide support for the skewer and do it by hand!

Alternatively, if you are feeling really adventurous,

you can construct a solar motor, which will turn the

skewer of your hot dog automatically!

First of all we need to construct the parabolic

mirror. The parabolic mirror collects all of the

solar energy and focuses it onto our hot dog. You

You will need

can read more about this effect in the chapter on

Solar Collectors (Chapter 8).

●

1381 IC

●

2N3904 transistor

Have you ever tried bending a glass mirror?

It doesn’t work, the least you will end up with is

●

2N3906 transistor

seven years bad luck, and at worse you could end

●

3300 µF capacitor

Project 8: Build a Solar Hot Dog Cooker up with bloody hands.

●

2.2 k resistor

46

Project 8: Build a Solar Hot Dog Cooker

Figure 6-2

Solar hot dog cooker.

●

Solar cell

●

High efficiency motor

Online resources

The circuit for the solar motor is shown in

Figure 6-4, it is a simple circuit, and can easily be

Solar hot dog cookers on the web:

assembled on stripboard. Once you have constructed

www.motherearthnews.com/Green_Home_

the solar motor driver circuit, you are going to need

Building/1978_March_April/Mother_s_Solar_

to mechanically couple the motor to the skewer. You

Powered_Hot_Dog_Cooker

may find if your motor is powerful enough, that you

www.pitsco.com/the_cause/cause3inv.htm

can directly drive the skewer—it would be worth

www.energyquest.ca.gov/projects/solardogs.html

investigating bearings to ensure that your skewer

sci-toys.com/scitoys/scitoys/light/solar_

turns as freely as possible with a minimum of

hotdog_cooker.html

resistance. If you find your motor struggles to turn

www.reachoutmichigan.org/funexperiments/

the skewer, then use a “worm drive” to reduce the

agesubject/lessons/energy/solardogs.html

speed of the motor—while increasing torque.

Figure 6-3

Drive mechanism.

47

Figure 6-4

Solar motor circuit.

Project 9: Build a Solar Marshmallow Melter

a series of concentric circles in the Fresnel lens.

You will need

Now think of a magnifying glass—it is round and

circular, and “bulges” in the middle. If we look at

●

Marshmallows

the glass from side-on, we can see that both sides

●

Large Fresnel lens

of the lens are curved—but there is also a lot of

●

Tin foil

glass in the middle! A Fresnel lens “removes” some

●

Skewers or a toasting fork

of the glass from the middle, and flattens the lens

onto a sheet. Each little concentric ring that you see

In this project, we are going to collect the sun’s

on the flat Fresnel sheet, is a section of lens curve.

energy from a large area, and focus it to a point in

order to create localized heating.

Look at where the sun is in the sky, and hold

the Fresnel lens perpendicular to an imaginary line

One way of collecting the sun’s energy from a

between the sun and your marshmallow. Move the

large area is to use mirrors. We have already

lens to and fro along this line, and observe how the

explored this in the “solar hot dog cooker.” You

focused beam of solar energy changes on your

will read more about concentrating solar energy in

marshmallow. After a little bit of time, focusing the

the chapter on Solar Collectors (Chapter 8).

sun onto the marshmallow, you should see the

In order to perform this experiment, we are

candy begin to toast! No fire required—just the

going to need a Fresnel lens—again see the chapter

power of the sun!

on Solar Collectors for an explanation on how

these work.

Put the marshmallow on a skewer, and rest it on

the sheet of tin foil. We are going to use the Fresnel

Online resources

lens, to focus the sun’s rays onto the marshmallow.

When you look out of your window, there is no

Marshmallow melting web pages!

magnification or reduction of the image—the glass

worldwatts.com/marshmallows/solar_roaster.html

does not act like a lens; however, you will notice

www.altenergyhobbystore.com/marshmallow%

when looking through the Fresnel lens (not at the

20roaster.htm

sun!) the image appears much bigger and magni-

bellnetweb.brc.tamus.edu/res_grid/cuecee05.htm

Project 9: Build a Solar Marshmallow Melter fied. Why is this? If you look closely, you will see 48

Project 10: Cook Eggs on Your Driveway

Project 10: Cook Eggs on Your Driveway Using the Sun

Alaska! But if your climate permits, this is a nice

You will need

trick! If there is not as much sun as you would

like, try using reflectors to aim more solar energy

●

Eggs!

onto your pan!

●

Drop of oil

In fact, with simple solar cooking, I have even

●

Hot sunny day

heard of people baking cookies in their car by

simply putting a black baking tray with cookie

Tools

dough on their dashboard, and parking the car in a

sunny setting with the windows up. They then

●

Black tarmac driveway

return to the car at lunch to find a tray of cookies

●

Frying pan

and a “bakery fresh” smelling car. It sure beats a

Sometimes, on a hot sunny day, the black tarmac

Magic Tree for in-car air freshening!

can almost seem painful to walk on barefoot as

it is so hot. If you keep moving, your feet feel

fine; however, if you stand in the same place for

the same time, your feet feel very uncomfortable.

This is because the tarmac road surface has the

Online resources

ability to act as a thermal mass and store heat. If

you were to stand on say a flimsy piece of black

The following link is a great solar cooker site

card that had been left in the sun, it would feel

written specifically for younger kids.

warm to the touch; however, you would find that

pbskids.org/zoom/activities/sci/solarcookers.html

as soon as you stood on it, the heat would be

quickly dissipated—the card doesn’t have the abil-

ity to store the heat. So, if we want to cook an egg

on a sunny day . . .

Take a peek at Figure 6-5 for the ridiculously

simple method.

Take a frying pan, put it on a black tarmac sur-

face on a hot sunny day, put a drop of oil in the

pan and cover the frying pan for a while with a

sheet of glass. The pan is black, the tarmac is black

and so will have absorbed the sun’s energy. All of

this heat via one process or another will transfer to

the oil, and pretty soon you should have hot oil.

Now crack an egg, and you will find that it

cooks—once again cover the pan with a sheet of

glass. Of course, this trick requires the right sort of

day—don’t expect fried egg on a cloudy day in

Figure 6-5

Solar egg frying.

49

Project 11: Build a Solar Cooker

Construct a box for your cooker out of MDF. I

You will need

find small veneer pins to be very useful as they can

be hammered neatly into the end grain of thin MDF

●

Sheet of thin MDF

without splitting the wood. For this application

●

Sheet of flexible mirror plastic

they are perfectly strong enough. When you have

●

Sheet of thin polystyrene

finished the box it should look something like

●

Veneer panel pins

Figure 6-6.

Now you need to line the box with polystyrene,

Tools

this will prevent the heat from escaping. The lined

box will look like Figure 6-7.

●

Bandsaw

Now measure the size of the cube inside the

●

Pin hammer

lined polystyrene box. You should cut the mirror

●

Sharp knife/scalpel

plastic to this size, and further line the box with it.

Duck Tape is more than ideal for making good all

●

Angle marking gauge

of the joints and securing things into place.

This solar cooker is a very simple project to

construct—we will be harnessing the sun’s energy

We now need to cut the mirrored reflectors. Cut

from a relatively wide area and concentrating it to a

a strip of mirror plastic about two feet wide on the

smaller area using mirrors (read more in Chapter 8

bandsaw. Now, using an angle marking gauge,

about this). The area which we will concentrate it

mark from the long side of the mirror to the very

into will be lined with polystyrene to keep in

corner of the mirror, a line which makes an angle

the heat.

of 67°, forming a right-angled triangle in the scrap

piece of plastic. You now need to mark out a series

of trapeziums along this length of mirror, where

Project 11: Build a Solar Cooker Figure 6-6 The box constructed from MDF.

Figure 6-7

The box lined with polystyrene.

50

Project 12: Build a Solar Camping Stove

Figure 6-8

The mirrored reflectors cut ready.

the shortest side is equal to the length of the inside

of the box cooker (Figure 6-8).

Now take the mirrored reflectors, and on the

Figure 6-9

The solar cooker ready and complete.

nonreflective side, use Duck Tape to join them

together to form the reflector which will sit on the

top. Using Duck Tape allows you to make flexible

hinges, which allow the reflector to be folded and

When the cooker is finished it will look like

stored out of the way.

Figure 6-9. It is now ready for cooking!

Project 12: Build a Solar Camping Stove

the other two should be joined up by their short

You will need

edges. Make the joint using adhesive tape so that it

is flexible.

●

Five sheets of A4 or U.S. letter size cardboard

Now cover the two pieces you are left with in tin

●

Tin foil

foil. Use glue to secure the foil.

●

Glue

And that is it! Now all it comes to is setting up

●

Adhesive tape

your stove.

Determine which way the sun is facing, and

Tools

orient the three panels so that they all face the sun,

with the outer two tilted slightly inwards. Now

●

Scissors

take the two sheets, one will sit on the ground—

This is an incredibly simple construction for a

the food stands on top of this. The second sheet

solar camping stove.

should be slightly tilted up toward the can so that

Simply, take five sheets of cardboard—three of

any overspill light which misses the food is

them should be joined together by their long edges,

reflected back onto it.

51

Figure 6-10

The set-up solar stove.

The beauty of this design is that it is very simple,

can be assembled quickly, and fits into the space of

The Easy Lid Solar Cooker

a few sheets of cardboard in your backpack.

solarcooking.org/easylid.htm

The Minimum Solar Box Cooker

The set-up cooker is illustrated in Figure 6-10.

solarcooking.org/minimum.htm

Heaven’s Flame Solar Cooker

www.backwoodshome.com/articles/

radabaugh30.html

Online resources

The Cooking Family Solar Panel

solarcooking.org/cookit.htm

There are a lot of folk out there who swear by solar

Inclined Box Type Solar Cooker

cooking. All sorts of people have formulated

solarcooking.org/inclined-box-cooker.htm

different designs of solar cooker. While I have

Sun Pan Solar Cooker

presented a few designs that have worked for me,

www.sungravity.com/sunpan_overview.html

there are many, many other different types of design

Nelpa Solar Cooker

for different applications. I highly recommend that

solarcooking.org/nelpa.htm

you browse some of the following links in order to

Pentagon Star Coooker

find the solar cooker that is right for you.

solarcooking.org/PentagonStar.htm

The Tracking Solar Box Cooker

Dual Setting Panel Cooker

solarcooking.org/Cookerbo.pdf

solarcooking.org/DSPC-Cooker.htm

Fresnel Reflector Cooker

A cardboard and tinfoil cooker with two heat

www.sunspot.org.uk/ed/

settings.

The Reflective Solar Box Cooker

Solar Funnel Cooking

solarcooking.org/newpanel.htm

solarcooking.org/funnel.htm

Collapsible Solar Box Cooker

The Tire Cooker

solarcooking.org/collapsible-box.htm

solarcooking.org/tire_eng.htm

The Bernard Solar Panel Cooker

A solar cooker made from a recycled tire!

solarcooking.org/spc.htm

Project 12: Build a Solar Camping Stove

Continued

52

Solar Cooking Recipes

Online resources—cont’d

Baked potatoes

Parvarti Solar Cooker

This is a really nice cartoon about cooking

www.angelfire.com/80s/shobhapardeshi/

potatoes in the sun.

twelvesided.html

www.hunkinsexperiments.com/pages/potatoes.htm

Windshield Shade Solar Cooker

solarcooking.org/windshield-cooker.htm

A solar cooker made from an old car

windscreen reflector shade

Brewing tea

Double Angle Twelve Sided Cooker

solarcooking.org/DATS.htm

If you want to brew tea in a solar cooker, you can’t

A simple cooker design from cardboard

expect to get boiling water and then make your tea

and tin foil

conventionally—instead take a jar and a couple of

Parabolic Solar Cooker

tea bags, put the tea bags in the jar along with

www.sunspot.org.uk/Prototypes.htm

some clean water (which you might have even got

A solar cooker with an aluminum reflector

from your solar distilling apparatus!).

and card base

Solar Bottle Pasteurizer

Soups

solarcooking.org/soda-bottle-pasteurizer.htm

A pasteurizing device powered by the sun,

Soups are really easy to cook in a solar cooker.

and made from recycled materials

Furthermore, they are particularly forgiving if the

Solar Water Pasteurizer

amount of sunlight is suboptimal, as warmish

solarcooking.org/spasteur.htm

vegetable soup is quite acceptable whereas rawish

Solar Chimney Dehydrator

not fully cooked chicken is totally unacceptable!

www.littlecolorado.org/solar.htm

Simple plans to build a food drying device

powered by the sun

Nachos

Solar Cooking in the Peruvian Andes

www.sunspot.org.uk/Solar.htm

Everyone loves Nachos! So why not take a bag,

Solar cooking in the developing world

spread them in a bowl and cover with grated

cheese. Then place the bowl in your solar cooker

to melt the cheese and give you toasty hot nachos!

Solar cooking recipes

Bread

Potatoes

Take some old baked bean tins and paint them

For a start, cooking potatoes with a solar cooker dif-

black—you now have the perfect can for cooking

fers a bit from cooking them in a campfire, which

bread!

you are probably used to, because if you wrap them

To cook some simple French bread you will

in shiny reflective tin foil, the solar energy which

need a packet of baker’s yeast, a tablespoon of

you have gone to painstaking ends to concentrate

sugar and a tablespoon of salt, five cups of white

onto the potato will simply be reflected!

flour and a couple of cups of water.

53

Dissolve the yeast in one cup of slightly warm

would be a great time to crack open the solar

water. Sift all of the dry matter into a clean bowl,

cooker and make the rest of the campsite jealous!

stir in the yeast—water mix, add the water from

You really want to cook on days when the sky is

the second cup in small amounts until the dough is

clear and the sun can easily be seen—on a cloudy

sticky. Grease a baked bean can which has been

day, cooking will be painfully slow.

painted black, being careful of any sharp edges,

One of the great things about solar cooking is

add the bread mixture and leave it in your solar

that you can prepare everything in advance, leave

oven.

it in your solar cooker, and when you return every-

thing is cooked ready to eat—whereas your

accomplices cooking with traditional methods still

Solar cooking tips

have to muck about and cook their food!

Also—think like this—if you are cooking using

In many campsites and caravan parks, open fires

conventional energy inside a home that is air

are banned because of the mess they produce and

conditioned, for every kWh of energy you input to

the smoke which can be unpleasant for other

your cooker, your air conditioning will use about

visitors—so while everyone else has run out of gas

another three trying to remove that heat from your

in their cylinder, or is eating cold raw food, now

home!

Solar Cooking Tips

54

Chapter 7

Solar Stills

A solar still effectively creates the hydrological

Water—a precious

cycle in miniature in an enclosed volume. The idea

is that by evaporating water, all of the bacteria,

resource

salts and other contaminants are left behind, with

the precipitate being pure, drinkable water.

The former World Bank Vice President Ismail

Even seawater can be desalinated using this

Serageldin, said that “the next world war will be

process.

over water.”

There are a number of advantages to solar

At first look, this statement seems almost non-

distillation:

sensical, we are surrounded by water, it falls from

the skies and runs through our streams and rivers;

●

Free energy

however, not all of the world enjoys such plenti-

●

No prime movers required

ful access to water as we do in the developed

world.

In much of the developing world the land is arid,

History of the solar still

and clean drinking water can often mean a walk

for tens of miles. This problem is exacerbated by

Solar stills are an old, tried and tested technology—

heavy industry building factories which extract

the earliest record of a solar still being used is in

what little water there is.

1551, when Arab alchemists used one to purify

Our water is constantly recycled by the natural

water.

environment, it follows a pattern called the hydro-

Mouchot, whose name also springs up a couple

logical cycle, which can be very simply repre-

of other times in this book also worked with solar

sented by Figure 7-1.

distillation around 1869.

Water evaporates from the earth, plants, animals,

and people, is carried far up into the sky where it

condenses to form clouds—then it precipitates

back to earth in the form of rain.

This has a purifying effect on the rainwater,

as when the water evaporates, contaminants are

left behind—or at least this used to be the case—

sulfur dioxide and other nastiness in the air

from human activity can be collected by the

rain as it precipitates, with the effect that when

it lands on the earth, it is acidic. This can cause

problems for plants and alkaline rocks, which

are damaged by the acid content of the rain.

Figure 7-1

The hydrological cycle.

55

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

The first solar still, in the sense that we would

The plant produced in excess of 6,000 gallons of

recognize it now, was built in the mining commu-

water a day.

nity of Las Salinas in 1872, in the area which is

The plant was effective and produced water well

now northern Chile. It was created by a Swedish

into the 20th century until it was finally closed in

Still technologist by the name of Charles Wilson. The

1912. All that remains now are shards of glass and

plant was massive, about 4,700 square meters—

salt deposits in the area where the stills were origi-

quite an engineering feat for the time.

nally constructed.

Project 13: Build a Window-Sill Demonstration Solar Still

Now take some clear plastic such as cling film/saran

You will need:

wrap and stretch it over the top of the pint glass.

You might want to anchor it around the perimeter of

●

Pint glass

the glass using a little bit of Sellotape just to make sure.

●

Egg cup

You will want to stick your finger into the plastic in

●

Cling film/Saran wrap

order to stretch it a little bit and create a dip above the

●

Sellotape

egg cup. Be careful not to stick your finger through!

●

Penny

You might want to put a little weight, such as a

●

Tea bag

small coin, here in order to preserve the dip. Your

whole assembly should now look something like

Tools

Figure 7-2.

●

Scissors

●

Kettle

This is a demonstration of how solar still technol-

ogy works. It works great as a science fair demon-

stration piece, and is of a size that you can quickly

put it together in a few minutes. This is how it

works.

First of all, we are going to make our water brack-

ish. The best way to do this is to put the kettle on!

A few minutes later, after making a brew you have

black tea. Allow the teabag to sit in the water for

some time until the water is quite “muddy.”

Now put your egg cup in the bottom of the pint

glass, and while holding the egg cup out of the

way, carefully pour the tea into the bottom of the

Project 13: Build a Window-Sill Demonstration Solar “still” making sure not to get any in the egg cup.

Figure 7-2

Demonstration solar still.

56

Project 14: Build a Pit-Type Solar Still

Put the glass on a south-facing window sill and

leave it for a couple of days. After some time, the

plastic on top of the still will look something like

Figure 7-3.

This water should taste clear and pure, not

“brackish” (i.e. strong tea!).

Now you have proved the operation of the solar

still!

Figure 7-3

Precipitated water in the demonstration still.

Project 14: Build a Pit-Type Solar Still

You will need:

First of all, you will need to dig a hole with a

●

Polythene sheet

spade. In this hole, you can place green plants,

●

Cup

cacti, pots of brackish water or anything else

●

Tube

you can gather that could potentially be water

●

Rocks

bearing.

In the middle of this hole, you need to put

Tools

a small cup, bowl or receptacle for water. A

tube runs from this receptacle to outside the

●

Spade

hole. Water can be extracted using this tube

This type of solar still is ideal if you are camping

without having to upset the solar still or dis-

in a hot climate or stuck in the desert and you need

mantle it.

to extract some clean drinking water.

Over the top of the still you need to put a clear

polythene sheet. This should be weighted down

around the edges using rocks and stones. A small,

Warning

light weight should be put in the center dip in

order to let the water settle to a point for collec-

On any camping expedition, remember to take

tion. This is shown in Figure 7-4.

sufficient water with you for the amount of

people and time you will be away. This type of

Water will precipitate and collect in the receiv-

still should only be used as a demonstration or in

ing vessel over time. In order to collect the water,

emergencies, and does not provide a consistent

just give a little suck on the pipe as shown in

reliable method for providing water for your

Figure 7-5 and pure water will come from the

travels, beyond basic, emergency needs.

still.

57

Figure 7-4

Diagram of a pit solar still.

Figure 7-5

A solar still in operation. Image courtesy © U.S. Department of Agriculture—Agricultural Research Service.

Project 15: Build a Solar Basin Still

●

Metal U-strip

You will need:

●

Black silicone

●

Plywood/oriented strand board

●

Low-profile guttering

●

Framing

●

Low-profile guttering end pieces

●

Screws

●

Tube

●

Project 15: Build a Solar Basin Still

Glazing (glass/polycarbonate)

●

Two stop cock valves

58

Project 15: Build a Solar Basin Still

of the wooden box so that it gets a thin uniform

Tools

coat. Less important are the sides, but you should

ensure that by the time you are finished, the inside

●

Jigsaw

of the box is fully lined with silicone.

●

Screwdriver

At the front of the still, that is to say on the

●

Squeegee

shortest side of the box, you need to make a small

This project is scaleable depending on your require-

gutter. This gutter will serve to collect your puri-

ments for water, which is why no specific mea-

fied water which will run down by the force of

surements are presented.

gravity from your glazing. You need to make this

First of all, you will need to calculate your water

gutter out of a waterproof material. The low-profile

needs. Solar stills can generally produce around a

guttering sold for sheds and outbuildings is ideal.

gallon of water per 8 square feet, this is around

A hole needs to be drilled in the side of the frame

four liters per square meter. This assumes that your

of your still, and a pipe introduced to allow you to

collector receives 5 hours of good sunlight per day.

siphon off the clean water.

Obviously the performance of your still will be

The silicone has two functions. First of all,

highly variable, depending on the amount of sun

it acts as a black collector surface, absorbing

your collector receives.

radiation and creating heat. But secondly, it pro-

You need to construct a wooden box from ply-

tects your wood by making the enclosure water-

wood or oriented strand board, with gently sloping

proof.

sides. This is well within the capability of someone

On top of this sealed box you need to put a sheet

with even modest carpentry skills.

of glazing. This needs to be sealed around the

At a position near the tallest side of the box you

edges with frame sealant to ensure a good water-

will need to drill a hole and insert a pipe with a

tight fit.

valve that can be opened and shut, to allow you to

The brackish water should never be allowed to

introduce brackish water to be purified.

rise above the level of the guttering, as it would

Then, take a squeegee and some black silicone.

contaminate the clean water. The whole solar still

You need to spread this mixture on the bottom face

is illustrated diagrammatically in Figure 7-6.

Figure 7-6

Diagram of the basin type still.

59

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Chapter 8

Solar Collectors

The sun provides an abundance of energy over a wide

In the book Epitome ton Istorion, John Zonaras

area; however, often our solar devices are fairly

wrote: “At last in an incredible manner he burned

small, and so receive little solar energy. So—what if

up the whole Roman fleet. For by tilting a kind of

we could take the solar energy from over a wide area,

mirror toward the sun he concentrated the sun’s

and concentrate it into a smaller area? This makes a

beam upon it; and owing to the thickness and

lot of sense, because it means that the small area

smoothness of the mirror he ignited the air from

receives a much higher amount of solar radiation.

this beam and kindled a great flame, the whole of

which he directed upon the ships that lay at anchor

in the path of the fire, until he consumed them all.”

So what can solar

This deadly weapon was allegedly used in the siege

collectors actually do?

of Syracuse in 212 BC—like I said, the idea is old!

So this is what MIT did . . .

Actually, the sun has quite a phenomenal power—

First they got loads of students on the 2.009

when concentrated into a small area, its power is

course, loads of chairs to act as stands and loads of truly extraordinary. If you were a ghastly child you

mirrors (Figure 8-1). Being MIT, they got the cash

might have burnt ants using a magnifying glass—

for this kinda stuff!

well what goes around comes around: remember

Next they lined all the mirrors up so that the sun’s

that when a large ethereal figure holds a magnify-

energy was concentrated onto the model of the

ing glass over you. One of my memories of junior

hull of a boat—voila!—or should that be Eureka?

school was gathering in a corner of the playground

Flames! (Figure 8-2)

where a group of children were concentrating the

sun onto some logs covered in tar and making

Here we can see the serious damage done by the

smoke. Although we did not know it then, we had

flames to the wood (Figure 8-3)! With a larger mirror

made a solar collector.

area this could have been a formidable weapon!

The chances are you’re getting tired of reading

In Figure 8-4 we see how MIT used a similar

this, but “this is not a new concept,” in fact, the

technique to the one you will use in the next

Greek’s purportedly had a “weapon of mass

project—cover each mirror up with paper, line

destruction,” that harnessed the power of the sun to

each one up individually by removing the piece

set fire to enemy boats.

of paper and adjusting the mirror. And then,

when they are all lined up, remove all the bits of

Archimedes—you may have heard of him—he

paper as fast as you can without disturbing the

found a few things out, like the concept of the

mirrors!

Archimedes screw and the theory of displacement.

Anyway, it is fabled that he had a weapon that was

And as ever, with every serious piece of techno-

created out of mirror-like bronze that he could use

logical investigation, there is the back of the paper

as a death ray—this ray essentially reflected

bag calculation (Figure 8-5).

concentrated sunlight!

Now it’s your go!

61

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Figure 8-1

Students, chairs and mirrors! Image courtesy Massachusetts Institute of Technology.

Figure 8-2

The boat catches fire—Archimedes was right. Image courtesy Massachusetts Institute of Technology.

Solar Collectors

62

Solar Collectors

Figure 8-3

The burnt hull. Image courtesy Massachusetts Institute of Technology.

Figure 8-4

Lining up the mirrors. Image courtesy Massachusetts Institute of Technology.

63

Figure 8-5

Working it all out! Image courtesy Massachusetts Institute of Technology.

Project 16: Build Your Own “Solar Death Ray”

You will need:

Warning

●

Sheet of MDF

●

Sheet of flexible mirror acrylic

I have used acrylic mirror in this project because

it is very easy to work with, and can be cut easily

●

72 long self-tapping screws

using a band saw; however, there is nothing to

Optional

stop you using a glass mirror if it is available and

you have the correct tools to cut it and work with

●

Silicone sealant

it—my only advice is it will be harder to work

with and much more fragile.

Tools

OK, so you have finally decided—the time is nigh

●

Drill bit

to melt your little brother. While he might be hard

●

Hand/cordless drill

to melt, you can certainly singe him with this mod-

●

Glue gun and sticks

ular solar death ray!

●

Ruler

Don’t worry—you won’t need lots of chairs and

●

Set square

big A4 mirrors like the guys at MIT! Instead, this

●

Bandsaw

modular death ray relies on little tiles which are

cut from plastic mirror.

Optional

The plan is really simple—you build the death

Project 16: Build Your Own “Solar Death Ray” ● Mastic gun ray a tile at a time. One tile is good to experiment

64

Project 16: Build Your Own “Solar Death Ray”

with, but once you become more confident and

want to expand, you can simply add more tiles!

To begin with, I recommend that you cut your-

self a piece of MDF that is 36 cm square, although

please bear in mind that this measurement is wholly

arbitrary.

Now using a ruler and set square, divide the

sheet into a matrix of six squares by six squares.

This will give you thirty-six equal squares 6 cm

square. Now, using the ruler and set square, draw a

line 1 cm either side of each line making up the

squares. This will leave you with a sheet that does

not look dissimilar to Figure 8-6.

You are now going to drill holes for the screws

that will support the mirrors. You will need to

select a drill that is slightly smaller than the screw

that you are going to drill the hole for. However,

Figure 8-7

Furnace drilling diagram.

please note that the screw does not need to be a

tight fit in the hole, as it would be if you were

Once you have drilled all 72 holes, you are

joining two pieces of wood. Instead, the screw is

going to need to think about getting those screws

only going to be used for light adjustment, so the

in place. This is a really tedious job, so either ask a screw can be a relatively slack fit in the hole.

younger sibling, or failing that, if you are an only

Looking at your board of squares, you are going

child you might like to consider investing in an

to be drilling two holes in each 6 cm square. The

electric screwdriver—the lazy man’s way out.

holes will be at the top left and bottom right,

You want to put the screws in so that they just

where the lines cross to form the smaller square

protrude from the other side a little way (Figure 8-8).

inside each square. Sounds confusing, well, take a

Now is a good time to take your acrylic sheet

look at the furnace drilling diagram (Figure 8-7),

of mirror, and, on a bandsaw, cut 36 identical

which shows where to drill in each square.

Figure 8-6

Sheet of MDF marked out.

Figure 8-8

Solar furnace with the screws in place.

65

6 × 6 cm squares. An easy way to do this is to set

Eventually you will find that you can focus all

the gate on your band saw to 6 cm from the blade.

of the mirrors onto a single point—this concen-

Take a couple of cuts from your mirror, to give you

trated energy can be used for cooking, heating, or

6 cm strips, and then cut these strips into squares

experiments (burning things!).

using the gate at the same measurement.

Once you have done this, you need to fix the mirrors

to the base plate of the solar furnace. You need to pick

a corner, which is different to the ones that the screws

Parabolic dish concentrators

are positioned in, and stick to this corner. What you

will be doing is applying a large glob of either glue or

Dishes are great for concentrating dispersed energy

silicone sealant, into which the corner of the mirror

to a focal point. Take a look at any residential neigh-

tile is immersed. The other two corners are supported

borhood, and you are bound to see a menagerie of

on screws, which permit adjustment of the tile’s angle

dishes (the state flower of Virginia) sticking out of

relative to the base board (Figure 8-9).

the side of houses everywhere! What do you think

When all the mirrors are in place, stick a small

these dishes are doing? Acting as concentrators!

removable piece of paper, for example a Post-It

They take the waves emitted from satellites far above

note to each of the mirrors.

the earth’s surface, and concentrate them into a focal

point which strengthens the signal. Similarly, you

Set your collector up so that it faces the sun. Remove

might have seen some of the world’s great radio tele-

one of the pieces of paper in one of the corner mir-

scopes perched up high upon hillsides. These are

rors—notice where the light forms a bright patch and

doing exactly the same thing, taking the signal from

set up an object to be heated or piece of wood there.

a wide area, and focusing it down to a small point.

Draw an X where there is a bright patch.

They are “concentrating” the weak signals from outer

Now, one by one, using the screws for adjust-

space to a fine point where they can be processed.

ment, you can change the angle of each individual

Solar concentrators using parabolic dishes are

mirror. Cover and uncover mirrors one by one

exactly the same, the difference being the medium

using the Post-It notes—you will need to work

used to coat the dishes. Rather than being reflec-

quickly as you will find that the sun is constantly

tive to radio waves, the coatings used to coat a par-

changing position.

abolic solar reflector are mirrors.

Again this idea is not particularly new, in fact,

back in the 1800s a Frenchman by the name of

Augustin Mouchot was actively experimenting with

using solar dishes to concentrate the sun’s energy.

Mouchot was concerned that coal was all going to

be used up and that “Peak Coal” was approaching.

He said at that time “Eventually industry will no

longer find in Europe the resources to satisfy its

prodigious expansion . . . Coal will undoubtedly

be used up.” One of Mouchot’s solar concentrators

can be seen in Figure 8-10. A little later in 1882,

Abel Pifre, Mouchot’s assistant, demonstrated a

printing press in the Tuilleries Garden, Paris, powered

Figure 8-9

Board with mirrors stuck on starting to

by the sun, using a 3.5 m diameter concave concentrat-

Project 16: Build Your Own “Solar Death Ray” take shape!

ing dish. At the focus of this concentrating furnace,

66

Parabolic Dish Concentrators

Figure 8-10

One of Mouchot’s solar furnace dishes.

was a steam boiler which provided steam for the

printing press. A woodcut drawing of this press is

Note

shown in Figure 8-11.

Dishes are great for concentrating dispersed energy

If you want a cheap source for a solar parabolic

to a focal point (Figure 8-12a and b). Take a look at

mirror, the University of Oxford produce a solar

Figure 8-13 which shows parallel rays of light, enter-

energy kit (Figure 8-14), which is inexpensive, and

ing a parabola and being focused to a point.

comes with a budget plastic parabolic mirror.

Figure 8-11

Pifre’s solar printing press.

67

Figure 8-12a and b

Parabolic mirrors take incoming parallel light (from the sun) and focus it to a point.

Figure 8-13

Diagram showing how parabolas focus light to a point.

Parabolic Dish Concentrators

68

Project 17: Build Your Own Parabolic Concentrator

Figure 8-14

University of Oxford solar energy kit.

Project 17: Build Your Own Parabolic Dish Concentrator

This is an incredibly easy way to make a parabolic

You will need

dish concentrator, and even better, it recycles old

stuff! Take a satellite dish, and dunk your adhesive

●

Old satellite dish

comb into the bathroom/kitchen tile adhesive.

●

Bathroom/kitchen tile adhesive

Working from the center of the dish outwards, spread

●

Small mirror tiles

the adhesive using the “comb” side of the spreader.

What the comb does is apply the adhesive in a

Tools

ridged manner, this means that when you press the

tiles into the adhesive, they have room to settle and

●

Adhesive comb

even themselves out. If you just apply straight flat

●

Spreader

adhesive, when you try to push the tiles in,

adhesive will ooze out everywhere and make a

mess. As you work from the center, keep adding

more tiles, trying as best you can to keep them in

Note

line with the plane of the parabolic satellite dish.

You need to purchase some tile adhesive—the sort

of stuff you would use when applying ceramic tiles

Caution

onto your walls at home.

You will need to choose a tile adhesive which

I strongly recommend that you perform this operation

is waterproof, as a non-waterproof tile adhesive

in your garage or in a shaded area, as with the addi-

will not stand outside use—for this purpose

tion of more mirrors and a little sunlight, a focal

kitchen/bathroom adhesive is strongly recom-

point can quickly develop which has the potential to

mended.

burn you while you are working!

69

150 kW of power during the day, enough to power

40 homes.

Note

Each dish comprises 82 individual mirrors all

If you are messy and get adhesive everywhere, you

focused to a single central point (Figure 8-15). This

want to wait a little while until the tiles are firmly

causes a massive amount of heat to be generated at

in place, but not so long as for the adhesive to dry,

that point which is used to drive a Stirling engine.

as it will only be harder to get off once it has set.

The Stirling engine produces mechanical movement,

To remove adhesive while it is still wet, you need a

which is converted to electrical energy by a conven-

moist cloth, which you can wipe over the surface

tional generator arrangement (Figure 8-16).

of your mirror tiles, taking off any excess adhesive

One of the problems inherent with solar dish

with the cloth.

systems is that they must track the sun—older

Concentrator

systems used really heavy mirrors which meant

that the motors required to track the sun had to be

Free energy?

big and beefy and drew a lot of energy. With this

new array of collectors, the mirrors have been

Solar dish collectors take the immense power of

designed with a honeycomb structure so they are

the sun, over the area of a dish, and concentrate

strong, and yet very light indeed.

that energy by means of reflectors to a central

This is said to be the largest array of solar dishes

point.

in the world, but big plans are afoot. Eventually,

At the end of 2004, Sandia National Laboratory

when the technology is fully proven, massive

announced that they were working with Stirling

arrays of 20,000 units are imagined filling vast

Energy Systems to build and test a six-dish array.

fields and plains—producing free energy from the

These six dishes would be capable of producing

sun (Figure 8-17).

Project 17: Build Your Own Parabolic Figure 8-15 Solar dish engine system under test. Image courtesy Sandia National Laboratories/Randy Montoya 70

Free Energy?

Figure 8-16

10 kW solar dish Stirling engine water pump. Image courtesy Sandia National Laboratories/

Randy Montoya.

Figure 8-17

Artist’s rendering of a field of solar engines. Image courtesy Sandia National Laboratories/

Randy Montoya.

71

Project 18: Experiment with Fresnel Lens Concentrators

small with a fairly coarse lens, but will certainly

You will need

do the job and provide many fun hours of

experimentation!

●

Fresnel lens

Fresnel lenses are often sold in small credit card or

●

Feather

slightly larger sized flat plastic printed versions in

●

Small piece of rubber

bookshops. They are often sold as a bookmark,

●

Wax candle

which doubles up as a text magnifier for those with

●

Photovoltaic cell

poor sight. These lenses are not normally that large;

however, they have quite a finely ruled lens structure.

●

Multimeter

Imagine trying to build a large lens to cover a meter

Overhead projectors are another great source of

square in order to concentrate the sun. What would

Fresnel lenses. If you can find an old projector which

you build it out of? Well for a start, the lens would

is being discarded, the Fresnel lens is the surface on

be physically quite big if it had to cover a meter

which you would place the transparency. As many

square, it would also use quite a large volume of

people are now switching to video projectors and

material. This is not a particularly efficient way of

presentation software, colleges and schools are often

doing things. Far better to build a lens that uses less

great places to find unwanted overhead projectors.

material. This has a number of advantages. First of

Old large screen projection televisions are another

all, it uses less material. As a result of this, the lens

item that sometimes use large Fresnel lenses to

is not only cheaper, but also lighter. This means if

our lens is actively tracking the position of the sun

by a mechanism, the mechanism can be lighter duty,

as it does not need to move such a heavy load.

Note

Very large Fresnel lenses can generate truly

awesome power—start the experiments in this

chapter with smaller Fresnel lenses such as those

used as “magnifying bookmarks” before

graduating to larger lenses!

Where can I get a

Fresnel lens?

Here are a few ideas for procuring a Fresnel lens,

both second hand and new, cost varies widely:

Car reversing lenses are a great source, like

Project 18: Experiment with Fresnel Concentrators those pictured in Figure 8-18, these are often fairly Figure 8-18

Car reversing Fresnel lens.

72

Project 18: Experiment with Fresnel Concentrators

make the picture larger. This will involve a bit of

disassembling—so make sure you are with someone

who knows what they are doing. Try to find an old

broken set, not your father’s latest HDTV wonder if

you want to live to see your next birthday!

Also, for a nice-sized meaty Fresnel lens, you

can often find plastic screens that you put in front

of your TV in order to make it appear bigger.

If all else fails, a quick Google search will throw

Figure 8-19

Diagram showing how a Fresnel lens

up a few results for optical suppliers. There are a

compares to a conventional lens.

lot of vendors selling kits to make large-screen

projector TVs from an old screen—these lenses are

to be lighter, they do not possess the same optical

often very overpriced. Online auction sites are

clarity as ordinary lenses—which is why they are

another good source, or school science catalogs.

not used in cameras or microscopes.

There are also a couple of entries in the Supplier’s

Take a look at Figure 8-20. It demonstrates that

Index (see Appendix) for new Fresnel lenses.

although our Fresnel lens is only a thin sheet of

plastic, it can magnify things significantly.

How does a Fresnel lens work?

Now try and use your Fresnel lens as a solar

concentrator, hold it above a piece of paper until

To understand how a Fresnel lens is constructed

you form a bright white dot of sunlight (Figure 8-21).

and works, we are going to need to do a little

Notice how much brighter the concentrated dot is

thought experiment. Picture this. You have a glass

compared with the rest of the paper, which is

lens which is flat on one side, and round on the

simply illuminated by the sun.

other. We are now going to use a tool to remove

material from the center point of the lens. The tool

has a flat end. We are going to remove material

until the corners of the flat-ended tool just begin to

penetrate the round surface. We are now going to

use another larger tool to remove material from a

circle around the last. We are going to do this until

the tool just starts to break through the surface. We

are going to keep doing this with progressively

larger tools until we are left with a hollowed lens.

If you were to look at the inside of this lens,

what you would see is a series of flat “steps” cut in

concentric circles. Now imagine flattening out

these concentric circles so that they all lay in the

same plane. What you have constructed in your

mind is a Fresnel lens.

Take a look at Figure 8-19, it shows how a

Fresnel lens is simply a normal lens with the

unnecessary glass removed and flattened. It is

important to note, that although Fresnel lenses tend

Figure 8-20

A thin Fresnel lens shown magnifying.

73

Figure 8-21

Concentrating solar energy using a Fresnel lens.

The intensity of the concentrated light might be

A few experiments that you

enough to singe a feather, or even a thin shaving of

can do with a Fresnel solar

rubber from a balloon or latex glove.

concentrator

Try shining the beam of light onto a photovoltaic

cell connected to a multimeter and load—see how

Use a thermometer to measure the temperature of

it affects the amount of power produced.

the point where the sun’s energy is concentrated—

see what difference it makes if the bulb is covered

You might also want to see if you can melt a wax

in tin foil or black paper.

candle using the power of your concentrated light.

Project 18: Experiment with Fresnel Concentrators

74

Chapter 9

Solar Pumping

Pumping water is an essential task—we need water

display at the Centre for Alternative Technology,

to drink, wash, cook, and sanitize and irrigate with.

U.K. (Figure 9-2).

Water can be used for utility, or it can be used for

This has some interesting consequences for our

dramatic effect, creating tranquility and pleasant-

energy supply. The pumped power station at

ness in our surroundings.

Dinorwig, Wales, draws water up into a large

Using solar energy to pump water makes quite

reservoir using excess power from the grid. When

a bit of sense. Our demand for water often rises

there is a shortage of power, that water is allowed

when the sun is shining. Think of agriculture—

to flow down hill through hydroelectric generators,

there is more sun in the summer, and that is

producing power as it does so.

when we want pumped water to irrigate our

As we can see, there are many cogent reasons

crops.

for using solar energy to pump our water—now

We can use water features to enhance our envi-

let’s move on to some practical projects:

ronment, water naturally has a calming destressing

effect, and its importance is emphasized by disci-

plines such as Feng Shui.

Water can be used to add prestige to an area.

The U.K. Centre for Engineering and Manufacturing

Excellence (CEME) has a fountain outside, powered

by solar photovoltaics on the roof. This can be

seen in Figure 9-1.

Similarly at home, you use your water features

in the garden when the sun is shining, not when

the sky is gloomy and the weather overcast.

In this sort of application, the intermittency of

solar energy does not matter so much.

Also, water can be stored relatively easy. When

we actually pump it to our location doesn’t really

matter, as it can happily sit there in a tank. This

means that we can use a supply tank to even out

some of the intermittency problems.

There are other solutions to the problem; even in

low light, we can harness the energy that the sun

produces and store it in capacitors. When the

energy stored builds up to a sufficient level, a

small amount of pumping can be performed and

Figure 9-1

Photovoltaic-powered fountains enhance

the cycle repeats again. This is shown in the

the CEME, U.K.

75

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Figure 9-2

The solar pumping display at the Centre for Alternative Technology, U.K.

Project 19: Build a Solar-Powered Fountain

Adding a solar-powered fountain to your school,

As a rough guide, a calm, trickling waterfall will

home, or office is a great way to create a peaceful

demand between 1 and 2 gallons per minute (gpm),

relaxing atmosphere. The modern world demands a

or between 3 and 8 liters per minute (lpm) if you

lot of us, and it is nice to have some space where

are working in metric.

we can quietly go and relax and listen to the

For something with a little more razzmatazz,

soothing sound of trickling water.

you might like a plume of water shooting into the

First of all, you need to decide what sort of

air. This will generally demand a little more water,

fountain you want. There are a number of different

say 4–7 gpm or 15–27 lpm.

options here—you might want a plume of water

If you want the whole shebang with a cascading

jetting into the air, you might like to add a trickling

waterfall with a heavier current, then you really

brook waterfall to your garden, or you might want

need to be considering flow rates of around 7–16

a bell shaped fountain.

gpm, which works out as around 27–60 lpm.

Once you have decided on your feature, nip down

to the garden center to see what fixtures and fittings

they have in store. Regular pump fittings will often

Tip

specify the flow rate of the fixture, this essentially

means what volume of water can be pumped at what

If you need to convert flow of water between metric

rate, and also how high the water can be pumped.

and imperial, I suggest you nip along to:

We call this the “head” of water. We will size our

www.deltainstrumentation.com/calcs.html

Project 19: Build a Solar-Powered Fountain pump appropriately to produce this head of water.

76

Project 19: Build a Solar-Powered Fountain

Manufacturer’s figures can often be optimistic

panel slightly to give you adequate performance in

and sometimes unreliable. While the minutiae

poorer weather.

sometimes don’t matter, if you want to be sure and

If you can’t find a source of low-voltage DC

test flow rate, all you need is a gallon bucket and a

pumps, then take a trip to your local chandler or

stopwatch. Time how long it takes to fill up the

boat shop. They will often sell low-voltage pumps

bucket.

that are used to pump water out from the bottom of

boats. These are known as “bilge pumps” and

shouldn’t cost a lot of money.

Deciphering pump specifications

When you buy your pump from the manufacturer,

Siting your panel

it will state on it a number of figures, it should tell

you how high the pump will pump water, this is

You might want to heed the guidance given in some

known as the head. Furthermore, it should also state

of the other chapters in this book on correctly siting

the flow rate of the pump, which is how much water

your solar panel. Furthermore, you want to ensure

it will pump for any given period of time. What

that your solar panel is correctly insulated and

you need to realize, is that as you increase the

protected against the elements. The waterproof solar

demand for head, the flow rate will suffer. This is

panel showcase in Figure 9-3 is ideal and further-

really important to bear in mind when selecting

more, looks attractive.

equipment.

Don’t hide your panel, proudly display your solar

When you go to choose your pump, you need to

credentials, make it a part of the feature, as shown in

realize that there are pumps, and there are pumps!

the solar fountain at CAT (Figure 9-4).

The type that you require is a “DC submersible

pump.” A submersible pump is already water-

In order to keep things nice and simple, we are

proofed and will happily sit in the sump of your

just going to connect our solar panel directly to our

water feature. It sucks the water from the sump,

pump (see Figure 9-5). This is nice because it allows

and forces it out through a pipe. One of the

you to visually observe the relationship between the

beauties of this type of pump is that it does not

water flowing through your feature, and the amount

require “priming,” a procedure which is tiresome

of sunlight falling on your panel. It does, however,

and often required by some other pumps.

mean that in overcast weather your feature will

Hint

Remember the 10:1 rule for working out horizontal

distances of pipe. First of all, it assumes you are

using pipe that is about 1⁄2 in. or 12 mm. It requires

energy to pump water horizontally, so think to

yourself for every 10 units horizontally, it is the

same as 1 unit of head.

You need to pick a pump that has a similar

power rating to your solar array. Keep everything

to 12 V, and if at all possible, oversize the solar

Figure 9-3

Waterproof solar panel showcase.

77

perform poorly, if at all; but then who wants to be

outside when it is overcast!

Next, before committing to a feature, take your

pump, dump it in a bucket of water and connect it

to your panel to check that everything is working.

Check this setup in good light to ensure that it is

your setup, not the sun which is the problem.

Now you need to build a sump of some sort for

your pump to sit in. Again, a trip to the garden

center may yield a nice large-sized waterproof

container, butt, or bucket.

If you are feeling particularly energetic, you

could dig a hole in the ground, line it with fine

sand, ensuring that there are no sharp protruding

edges, and then line it with a waterproof liner.

You want your sump to be able to hold a fair

quantity of water—the water in our feature will be

recirculated, rather than constantly replenished.

Ensure that when your submersible pump sits in

the sump it is fully immersed in water.

Figure 9-4

Solar panel on display.

Project 19: Build a Solar-Powered Fountain Figure 9-5 Diagram of the solar water feature.

78

Project 19: Build a Solar-Powered Fountain

Things to consider

Hint

Flexible plastic tubing and jubilee clips are infinitely

Because of the low-voltage, low-current nature of

easier to work with than copper pipe and solder.

a single photovoltaic module connected to a

You will want to provide some sort of mechanical

pump, many region’s electrical codes will not

protection for your cable to ensure that it does not

require a fuse, breaker, or other disconnection

become chafed, or cannot easily be damaged by

device; however, check your local regulations to

gardening activities such as digging. Encase the

be on the safe side.

pipe in a hard plastic pipe, or mount it above

One you have satisfied yourself that your pump

ground where it can clearly be seen.

and module work together satisfactorily, you will

need to install your feature.

79

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Chapter 10

Solar Photovoltaics

A solar photovoltaic device is one which takes

The first generation of practical solar cells was

light from the sun and turns it into electricity. In

horrendously expensive, and this severely limited

doing so, it produces no emissions or harmful

their range of applications. The advantages of using

waste, and does so completely silently!

photovoltaic cells to turn sunlight into electrical

power were initially appreciated for powering

satellites and space-missions. With the space race

of the 1950s and 1960s, there was suddenly a

The origin of photovoltaic

good application for solar cells—despite the cost,

solar cells

solar cells were suitable for generating energy in

the remote reaches of space. Vanguard 1 was

None of this would be possible if it hadn’t been for

launched on March 17, 1958, and was the first

the work of French Physicist Edmund Becquerel,

artificial satellite to employ solar photovoltaic

who in 1839, discovered the photovoltaic effect. In

cells. With the injection of funding and research

fact, Becquerel is a bit of an inspiration for young

that came with the space race, solar cells began to

Evil Geniuses wanting to experiment with solar

come into their own. Over the years that followed,

energy, as he made his discoveries when he was

solar photovoltaic technologies have been refined

only 19! In 1883, Charles Fritts, an American

and developed and new techniques explored. We

inventor, devised the first practical solar cell, when

are now at the point where we have a range of

he took some selenium and covered it with a fine

different photovoltaic technologies, and we will

coating of gold. His cell wasn’t particularly efficient,

explore these now.

with 1% or so conversion efficiency from light to

electricity; however, his design of cell later found

applications as a sensor in early cameras to detect

the light level—being used to “sense” light rather

Solar cell technologies

than to generate power in any real quantity. Albert

Einstein went on to further develop the theory of

There are a number of different technologies that

the nature of light and the mechanism through

can be used to produce devices which convert light

which the photoelectric effect works, the discovery

into electricity, and we are going to explore these

was considered so important that he won the Nobel

in turn. There is always a balance to be struck

Prize in 1905. Because of their high cost and low

between how well something works, and how

efficiency at that time, there were a lack of

much it costs to produce, and the same can be said

applications for photovoltaic cells. It was not until

for solar energy.

Bell Laboratories started looking at the idea again

We take solar cells, and we combine them

in the 1930s that Russell Ohl discovered the silicon

into larger units called “modules,” these modules

photovoltaic cell. This device was patented as

can again be connected together to form arrays.

Patent no: US2402662 “Light sensitive device.”

Thus we can see that there is a hierarchy, where

Now the efficiency of solar cells began to increase.

the solar cell is the smallest part (see Figure 10-1).

81

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Figure 10-2

Monocrystalline solar cells made into

a panel.

appears to be round or a square with rounded

corners; you can see monocrystalline solar cells in

Figure 10-2.

One of the caveats with this type of method, as

you will see later, is that when a silicon crystal is

Figure 10-1

Cells, modules and arrays.

“grown,” it produces a round cross-section solar

cell, which does not fit well with making solar

panels, as round cells are hard to arrange efficiently.

In this chapter we are going to look at the struc-

The next type of solar cell we will be looking at,

ture and properties of solar “cells,” but bear in

also made from silicon, is slightly different, it is a

mind, when combined into modules and arrays, the

“polycrystalline” solar cell. Polycrystalline cells

solar “cells” here are mechanically supported by

are still made from solid silicon; however, the

other materials—aluminum, glass, and plastic.

process used to produce the silicon from which the

One of the materials that solar cells can be made

cells are cut is slightly different. This results in

from is silicon—this is the material that you find

“square” solar cells. However, there are many

inside integrated circuits and transistors. There are

“crystals” in a polycrystalline cell, so they perform

good reasons for using silicon, it is the next most

slightly less efficiently, although they are cheaper

abundant element on earth after oxygen. When you

to produce with less wastage.

consider that sand is silicon dioxide (SiO ), you

Now, the problem with silicon solar cells, as we

2

realize that there is a lot of it out there!

will see in the next experiment, is that they are all

Silicon can be used in several different ways to

effectively “batch produced,” which means they

produce photovoltaic cells. The most efficient solar

are produced in small quantities, and are fairly

technology is that of “monocrystalline solar cells,”

expensive to manufacture. Also, as all of these

these are slices of silicon taken from a single, large

cells are formed from “slices” of silicon, they use

silicon crystal. As it is a single crystal it has a very

quite a lot of material, which means they are quite

regular structure and no boundaries between crystal

expensive.

grains and so it performs very well. You can gen-

Now, there is another type of solar cells,

Solar Photovoltaics erally identify a monocrystalline solar cell, as it so-called “thin-film” solar cells. The difference

82

Solar Photovoltaics

between these and crystalline cells is that rather

By contrast, thin-film cells are cheap to produce,

than using crystalline silicon, these use chemical

and the only factor limiting their shape is the

compounds to semiconduct. The chemical com-

substrate they are mounted on. This means that

pounds are deposited on top of a “substrate,” that

you can create large cells, and cells of different

is to say a base for the solar cell. There are some

shapes and sizes, all of which can be useful in

formulations that do not require silicon at all, such

certain applications.

as CIS (copper indium diselenide) and cadmium

We are now going to take a detailed look at

telluride. However, there is also a process called

making two different types of solar cell, one will

“amorphous silicon,” where silicon is deposited

be a crystalline solar cell, and the other a thin-film

on a substrate, although not in a uniform crystal

solar cell. Both of the experiments are designed to

structure, but as a thin film. In addition, rather than

be “illustrative,” rather than to actually make a cell

being slow to produce, thin-film solar cells can be

with a useful efficiency. The technology required

produced using a continuous process, which makes

to make silicon solar cells is out of the reach of the

them much cheaper.

home experimenter, so we are going to “illustrate”

However, the disadvantage is that while they

the process of how a solar cell is made, using

are cheaper, thin-film solar cells are less efficient

things you can find in your kitchen. For thin-film

than their crystalline counterparts. Some different

solar cells, we are going to make an actual solar

solar photovoltaic technologies are compared in

cell, which responds to light with changing

Table 10-1. Figures are given for the efficiency of

electrical properties; however, the efficiency of our

the cell technology, and the average area of cells

cell will be very poor, and it will not be able to

required to generate 1 kW peak power when facing

generate a useful amount of electricity.

in the right direction!

When looking at the merits of crystalline cells

and thin-film cells, we can see that crystalline

cells produce the most power for a given area.

How are crystalline

However, the problem with them is that they are

photovoltaic cells made?

expensive to produce and quite inflexible (as you

are limited to constructing panels from standard

In this section we are going to look at how photo-

cell sizes and cannot change or vary their shape).

voltaic cells (PV) are made. However, rather than

taking a dull, textbook approach, we are going to

make the whole process fun by doing some practical

Table 10-1

kitchen experiments that mimic the process that

Efficiency of different cell types

happens in solar cell factories all around the world.

Area required

to generate

1 kW peak

How do they work?

Cell material

Efficiency

power

First of all, let’s cover a little bit of the theory.

Monocrystalline silicon

15–18%

7–9 m2

Polycrystalline silicon

13–16%

8–11 m2

Ordinary silicon forms into a regular crystalline

Thin-film copper indium

7.5–9.5%

11–13 m2

structure. If you look at Figure 10-3, you can see

diselenide (CIS)

the way that the silicon atoms align themselves

Cadmium telluride

6–9%

14–18 m2

into a regular array.

Amorphous silicon

5–8%

16–20 m2

To make silicon “semiconducting,” we can take a

Source data: Deutsche Gesellschaft fur Sonnenenergie e.V.

little bit of another chemical, in this case boron, and

83

Figure 10-3

Plain old silicon—its atomic structure.

Figure 10-5

Silicon doped with phosphorus—note the

spare electron.

introduce it to the silicon. Where there is a boron

atom, there is also a missing electron. This creates

A photovoltaic solar cell is a bit like a sandwich.

a “hole” in the outer shell of the boron atoms and

It is made from layers of different types of silicon,

its neighboring silicon atom (Figure 10-4).

as illustrated in Figure 10-6.

If we add a little bit of phosphorus to our silicon,

Starting from the base, we have a large contact.

we get the opposite effect, a “spare” electron

Then on top of this we have a layer of p-type

(Figure 10-5), which doesn’t quite know where to

silicon, a junction called the space charge region

fit in. As a result, it sort of “lingers uncomfortably”

waiting for something to happen.

Now, we can use these two types of “doped”

silicon to make semiconducting devices, in this

case “photovoltaic cells.”

Figure 10-4

Silicon doped with boron—note the

Solar Photovoltaics missing electron.

Figure 10-6

Cutaway solar cell.

84

Project 20: Grow Your Own “Silicon” Crystals

where the magic occurs, and a slice of n-type

are “knocked” across the boundary between p- and

silicon on top.

n-silicon, which causes a flow of electrons around

On top of all this is layered a grid electrode,

the circuit.

which does the job of making the other contact.

We are now going to look at how the silicon

Now, photons from the sun hit our solar cell, and

for these solar cells is manufactured, using

in doing so “spare” negatively charged electrons,

some things you can do at home.

Project 20: Grow Your Own “Silicon” Crystals

that we are not going to run out of silicon in a

You will need

hurry!

The problem with sand is that it also contains

●

Plastic coffee jar (empty)

oxygen in the form of silicon dioxide, which must

●

Skewer

be removed.

●

Hardboiled egg

The industrial process used to produce silicon

●

Sugar

requires temperatures of around 3270∞F (which is

●

Food coloring

about 1800∞C). Obviously we can’t experiment

with these sorts of temperatures at home—but we

can recreate the process!

Tools

If you don’t want to get the individual bits and

●

Compass

bobs, a couple of educational scientific vendors

sell rock-growing kits. These links are to suppliers

●

Egg slicer

of kits of parts:

To make a photovoltaic cell we need silicon, this

project is going to show you how solar cells are

●

scientificsonline.com/product.asp?pn=3039234&

bhcd2=1151614245

produced from crystalline silicon. The words

“crystalline silicon” should indicate to you that

●

www.sciencekit.com/category.asp_Q_c_E_737919

this type of solar cell is made from crystals of

●

www.scienceartandmore.com/browseproducts/

silicon. We saw earlier how silicon aligns itself

Rock-Candy-Growing-Experiment-kit.html

into a regular crystalline array, now we are going

If you want to do it all yourself, then you can

to look at growing this crystal.

see from Figure 10-7 that the process is a relatively

In industry, silicon crystals are grown to form a

easy one! You are going to need a saturated sugar

uniform cylinder of silicon which is used as the

solution, this will sit in the lid of your coffee jar.

base material for crystalline solar cells. There is

Now, take a large crystal of sugar, often sold as

plenty of silicon about on the earth, in fact, as

“rock sugar” and “glue” it to the end of the skewer.

mentioned previously, after oxygen it is the second

Next, drill a hole the same diameter as the skewer,

most abundant element. When you think that sand

and poke the skewer through the bottom of the

and quartz all contain silicon and then imagine the

coffee jar. Stand it on a windowsill and lower the

amount of sand in the world, you begin to realize

crystal into the saturated sugar solution. Over some

85

Figure 10-9

Slicing eggs.

Once this large crystal of silicon has been manu-

factured, it must be cut into slices to manufacture

the solar cells. I like to think of this a bit like the

way an egg is sliced to make sandwiches by an

Figure 10-7

Growing sugar crystals.

egg slicer—see the analogy in Figures 10-9 and

10-10.

time, crystals should start to grow—pull the

skewer up slowly, bit by bit, so that the growing

“Slice and dope” your silicon

crystal is still in contact with the sugar solution.

crystals

This is just like the way that silicon is grown. The

Slicing an egg with an egg slicer is much like the

silicon is drawn up slowly from a bath of molten hot

process that happens when a solar cell is manu-

silicon (which is analogous to our saturated sugar

factured. Each slice of silicon is then called a

solution). This is shown in Figure 10-8.

“wafer.”

We now need to create a p–n junction in the

wafer; to do this phosphorus is diffused into the

surface of the silicon. Dip your egg into some food

coloring or beetroot juice, and you will see that the

juice covers one surface of the egg slice. Now,

imagine that slice of egg were a solar cell, with the

beetroot-soaked face pointing toward the light.

Imagine an electrical contact on either side of the

egg slice is connected to our circuit. The photons

Project 20: Grow Your Own “Silicon” Crystals Figure 10-8 Growing silicon crystals.

Figure 10-10

Slicing silicon.

86

Project 21: Build Your Own “Thin-Film” Solar Cell

hit the colored side, which is “doped” with phos-

phorus to produce some extra electrons. By giving

these electrons additional energy from the photons,

they are able to “jump” the gap, across to the

“boron” doped silicon (the plain old egg) where

they fill the “holes” where there are electrons

missing from the atomic structure. With a steady

Figure 10-11

stream of photons, hitting the cell, a heavy stream

Doping with phosphorus.

of electrons are encouraged to migrate across the

p–n junction, then travel around the circuit doing

useful work!

Now we have looked at the technology of

Now these cells can be integrated into larger

crystalline solar cells using silicon, let us turn our

modules, or even arrays, to produce more power.

attention to thin-film solar cells.

Project 21: Build Your Own “Thin-Film” Solar Cell

Tools

Note

●

Metal guillotine (optional)

First of all a little disclaimer ... the solar cell you

●

Bandsaw (optional)

are about to build here is horribly, horribly

●

Tin snips

inefficient. Please do not have any plans to use

these to power your home. The amount of current

●

Electric ring hob

that they produce is very small and not econo-

First of all, cut a square of the copper sheeting so

mically exploitable. While this is a shame, this

that it is about 6–8 in. square in size. It is

project is very interesting, educational and helps

much easier to do this with a metal guillotine

you get to grips with the photoelectric effect.

(Figure 10-12); however, if you haven’t got

access to this sort of equipment, tin snips will

work just fine.

You will need

When you have done this, wash your hands

thoroughly and dry them. You need to remove any

●

Copper sheeting

grease or oil from your hands that could cause

problems with the next step of the process. Remove

●

Clear Plexiglas/Perspex/acrylic sheeting

any grease or detritus from the copper sheeting. Next,

●

Some thin wood strip

take a piece of emery cloth (see Figure 10-13), and

●

Copper wire

thoroughly sand down the piece of copper on both

●

Duct tape

sides to remove the top layer of oxidized copper.

87

Figure 10-12

Cutting the copper with a guillotine.

This will leave you with nice bright shiny red

copper underneath.

You now need to heat treat the copper, in order

to form an oxide coating on top. It may sound

counterintuitive that we have just removed all the

oxide and now we are going to put oxide back on,

but the oxide coating we will be applying will be a

film of “cuprous oxide.”

You will need an electric hob to do this. If you

have any “heat proof gloves” and metal tongs, this

might be the time to get them in order to handle

the metal while hot.

You need to turn the burner to the highest

setting, with the sheet of copper just placed on top.

Observe the changes to the copper carefully, they

are very interesting.

As you heat the copper, it takes on a lovely vivid

patina of different colors. Obviously, the pages

here are black and white, so I can’t show you, but

if you look at Figure 10-14 a–e you will see the

Project 21: Build Your Own “Thin-Film” Solar Cell Figure 10-13 Cleaning the copper with emery cloth.

changes that the plate goes through.

88

Project 21: Build Your Own “Thin-Film” Solar Cell

Figure 10-14

The shiny copper plate on the burner.

you will find most of the black layer of oxide

comes off easily. If any bits are stubborn, do not

Hint

under any circumstances scour them, as we do not

want to damage the fragile surface.

If you have access to nitric acid, you can use this

as a superior method for removing the upper

Under this black layer of oxide, you will find

cupric oxide layer.

another layer of a reddish orange rust color. This is

the layer which is “photosensitive” and will make

our thin-film solar cell work.

You will see a black crusty oxide form on top of

the copper plate. If you leave the plate to cool

Make a spacer now from some thin strips of

slowly, the crusty layer should become fairly

wood (Figure 10-15). I used duct tape to join my

fragile and separate easily from the underlying

pieces of wood together—do not use metal fixings

copper. When you have allowed the plate to cool

as they could react electrolytically with the other

thoroughly, give the plate a firm bang edge-on to a

components of the cell.

hard surface. Some of the oxide will pop off. Rub

We are now going to make another electrode. It

the oxide gently with your fingers under a tap, and

has to have the property that it does not touch the

89

Cell

Solar

Figure 10-16

Perspex and duct tape.

Figure 10-15

The spacer piece.

You can experiment with different types of wire

and copper—the trick is to try and maximize the

other piece of the solar cell, and allows light to hit

surface area of the copper, while trying to block as

the surface. We are going to use salt water as our

little light as possible from reaching the solar cell.

other electrode, making contact with the whole

surface of the thin film cell, yet conducting electri-

Fold the duct tape over and stick the wire to

city. We are then going to immerse another copper

the plate.

Own “Thin-Film” wire to make the connection. You could equally We are now going to combine the electrode plate

use another piece of copper plate around the outside

with the space. Again, duct tape makes this a nice

of the thin-film cell, but not touching our oxidized

easy job (Figure 10-18).

copper.

Next, we are going to take the copper plate, and

In a commercial thin-film cell, tin oxide is com-

stick duct tape to one side, with the sticky side of

monly used as the other electrode, as it is clear and

the tape facing the same direction as the layer of

yet conducts electricity.

red copper oxide (Figure 10-19).

Now take a piece of Perspex to act as a cover

plate, and stick a strip of duct tape on either side,

as shown in Figure 10-16.

We are going to stick our other electrode wire to

this piece of Perspex.

In Figure 10-17, I have used thickish wire for

clarity, with few actual zigzags so that you can

clearly see what is going on. To optimize the

performance of your solar cell, you want to make

the conductor large. To this end, you are better

using lots of thinner gauge wire in a much finer

zigzag pattern—this will still allow the light to get

through, but at the same time gives a large

Project 21: Build Your conductor area.

Figure 10-17

Wire electrode.

90

Project 21: Build Your

Figure 10-18

Perspex plate and electrode combined.

Figure 10-20

The finished solar cell.

Combine the plate and the front module to make

the finished solar cell (Figure 10-20).

Now, take a little salt water, and fill the void

between the Perspex front section and the copper

Own

plate. Seal the module with duct tape all round to

prevent leakage.

Chemical data file: cuprous

Finally, connect your module to a multimeter,

oxide

“Thin-Film” Solar Cell

find a bright light source, and explore some of the

electrical properties of your solar cell.

Cuprous oxide (red)

Formula

Cu O

2

Molecular weight

143.08

Physical appearance

Red to reddish brown

powder

Experiments with

photovoltaic cells

In this project we will be performing a range of

experiments with photovoltaic cells that allow us

to learn something about their characteristics and

how they perform in different applications.

The experiments in this project could form

a great basis of a science fair stand or poster

Figure 10-19

The copper plate with duct tape fixings.

display.

91

Project 22: Experimenting with the Current–Voltage

Characteristics of a Solar Cell

You will need

●

Light source

●

Photovoltaic cell

●

Voltmeter

●

Ammeter

Figure 10-21

Circuit to determine the current–voltage

curve of a single solar cell.

●

Variable resistance

●

Graph paper and pencil

or

Now plot the points on your graph paper, or by

●

Computer with spreadsheet package

using the chart wizard on a spreadsheet program.

We can learn a lot about solar cells’ electrical

Compare your graph to Figure 10-22. The graph

characteristics by plotting the “current–voltage”

tells us how the solar cell will perform when

curve of the device.

different loads are applied.

To carry out the experiment, we will need to

ensure that the solar cell receives constant illumi-

nation all the time. Use a bright lamp, and position

it a fixed distance above the solar cell.

Set up the circuit as shown in Figure 10-21.

We are now going to adjust the variable resistor

from one extreme to the other, noting how the

readings on the voltmeter and ammeter change as

we do so. At this point you need to make careful

notes as to the current and the voltage at each

stage. You can do this on paper, or, if you have a

PC handy, on a spreadsheet. Try and take at least

15 or so different readings to help you plot an

Figure 10-22

Current–voltage characteristics of

accurate curve.

a single solar cell.

Project 22: Current–Voltage Characteristics

92

Project 24: Experimenting with Solar Cells

Project 23: Experimenting with Current–Voltage

Characteristics of Solar Cells in Series

You will need

●

Light source

●

Three photovoltaic cells

●

Voltmeter

●

Ammeter

●

Variable resistance

●

Graph paper and pencil

Figure 10-23

Circuit to determine the

or

current–voltage curve of solar cells in series.

●

Computer with spreadsheet package

Now we are going to repeat the experiment above,

but we are going to do it three times.

Set up the circuit as shown in Figure 10-23. First

using one cell, then two, then three.

You can reuse your result for above for the

single solar cell, but we are now going to add two

additional lines to our graph—one for two solar

cells connected in series, and another for three

solar cells in series.

What can we see from the results (Figure 10-24)?

Well, it is clear that when we add multiple solar

cells in series, the voltages “add up.” However, the

Figure 10-24

Current–voltage curve of solar cells

current produced remains the same.

connected in series.

Project 24: Experimenting with Solar Cells in Parallel

●

Ammeter

You will need

●

Variable resistance

●

Light source

●

Graph paper and pencil

●

Three photovoltaic cells

or

●

Voltmeter

●

Computer with spreadsheet package

93

Figure 10-25

Circuit to determine the

current–voltage curve of solar cells in parallel.

We are now going to connect solar cells in parallel

and repeat the experiment.

Figure 10-26

Current–voltage curve of solar cells

Again, we will end up with a graph with three

connected in parallel.

lines. Make a prediction now! How do you expect

this graph to differ from the one when we

connected solar cells in series?

The solar cells will be connected in accordance

with Figure 10-25. First connect one cell, then two

How do the two graphs differ? Well, it can be

in parallel, then three!

seen that in the parallel plots, the voltage remains

Now plot the graph from the points that you

the same throughout, and it is the current that

obtained (Figure 10-26) and compare it to

changes—contrast this to the series experiment

Figure 10-24.

where it was the voltage that changed.

Project 25: Experiment with the “Inverse Square Law”

the amount of received light is equal to the inverse

You will need

of the square of that distance (Figure 10-27).

As we are trying to measure the light only from

●

Light source

a point source, it is a good idea if you can try and

●

Photovoltaic cell

do this in a darkened room.

●

Voltmeter

Take a single solar cell, and connect a voltmeter

●

Ammeter

and ammeter across its terminals. We are going to

●

Variable resistance

move the light away and measure the voltage and

●

Graph paper and pencil

the current produced. Remember, it is easy to find

the total “power” produced by multiplying the

or

voltage and the current together. Compare the

●

Computer with spreadsheet package

power generated, to the distance that the light

The inverse square law says that for each unit of

source is from the solar cell. Plot this in a copy of

Project 25: The “Inverse Square Law” distance you move a light away from a solar cell, Table 10-2. What do we learn about the

94

Project 25: The “Inverse Square Law”

Table 10-2

Measuring power produced by a solar cell

when light is held at different distances

Distance Distance

Load

Short

circuit

(in.)

(cm)

voltage (V)

current (mA)

0

0

2

5

4

10

6

15

8

20

10

25

12

30

14

35

16

40

18

45

20

50

Figure 10-27

Inverse square law.

relationship between the light falling on the cell

and the power generated?

Our solar cell produces more power when there

is more light falling on it. We can repeat the

experiment for a current–voltage curve, with

different amounts of light falling on the solar cell.

What we learn is that the current–voltage

curve of the cell changes depending on the

amount of light falling on it. This can be seen in

Figure 10-28

How the current–voltage curve of the

Figure 10-28.

solar cell changes with varying illuminance.

95

Project 26: Experimenting with Different Types

of Light Sources

Table 10-3

You will need

Measuring power produced by a solar cell

with different light sources

●

Light source

Type of light

Load voltage (V)

Current (mA)

●

Photovoltaic cell

●

Voltmeter

Sunlight (sunny day)

Sunlight (dull day)

●

Ammeter

Sunlight (overcast day)

●

Variable resistance

Incandescent lamp

In this experiment we are going to look at the

Compact fluorescent

range of values for power produced from different

lamp

light sources. Take your solar cell, and connect it

Fluorescent lamp

in the same manner as when we measured current–

Ultraviolet lamp

voltage curves, and try different sources of light.

Orange sodium street

Plot the results in a copy of Table 10-3. How does

light

the power generated compare with natural light?

Project 27: Experimenting with Direct

and Diffuse Radiation

The concept that we are going to get to grips with

in this experiment is that reflected light can

You will need

produce an awful lot of illumination and hence

energy.

●

Light source

●

Photovoltaic cell

Look at the two types of radiation hitting the

solar cell in Figure 10-29. Now, using the tech-

●

Voltmeter

niques shown in Figures 10-30 and 10-31, shade

●

Ammeter

the solar cell from either direct or indirect

●

Variable resistance

radiation and note the amount of power that is

Project 27: Direct and Diffuse Radiation ● Paper to shade produced.

96

Project 27: Direct and Diffuse Radiation

Figure 10-29

Radiation hitting a solar cell.

How does the amount of power produced from

This means that they can absorb more power than

indirect radiation compare to that from direct

had they just been collecting light from one

radiation? There are solar cells available called

direction.

“bifacial solar cells” (Figure 10-32).

In Figure 10-33, they have been mounted on the

These solar cells are mounted on a clear sub-

roof of a covered walkway. In this application, the

strate to form a module. They have the advantage

solar cells are serving two purposes—generating

that they can collect light from both sides, so

clean energy, while keeping the rain off people

they can absorb direct and indirect radiation.

walking along the walkway.

Figure 10-30

Blocking indirect radiation.

Figure 10-31

Blocking direct radiation.

97

Figure 10-32

Bifacial solar cells.

Project 27: Direct and Diffuse Radiation Figure 10-33 Bifacial solar cells on the roof of a covered walkway.

98

Project 28: Measurement of “Albedo Radiation”

Project 28: Measurement of “Albedo Radiation”

You will need

●

Light source

●

Photovoltaic cell

●

Voltmeter

●

Ammeter

●

Variable resistance

●

Paper to shade

What is albedo radiation?

Figure 10-34

Measuring albedo radiation.

The ground is a surface just like any other, it has

the capability to reflect radiation so we must not

ignore it. Just think, black tarmac is bound to

reflect less radiation than say a light gray concrete.

Why are we bothered—our solar cells point

Applications of

toward the sky don’t they?

Well, yes, that is true in most cases; however,

photovoltaic cells

bifacial solar cells are able to accept solar radiation

on both faces.

We have explored some of the properties of indi-

vidual photovoltaic cells and seen how light can be

used to produce electricity, now let’s look at some

The experiment

applications of solar cells.

The next experiment may seem counterintuitive,

First of all, despite electricity from solar cells

but it is very worthwhile. We are going to be

currently costing much more than power from the

measuring albedo radiation. Using your solar

grid, solar cells can be useful for applications where

setup, point your PV panel at the floor and take a

there is not a nearby electricity supply, and where

measurement (Figure 10-34).

a connection to the grid could potentially be quite

expensive.

What did you expect? A zero reading? In fact,

as you can see, there is still a lot of energy in

We saw earlier, how the first solar cells were

“indirect” radiation which is reflected from other

used to power satellites in space (Figure 10-35),

surfaces. We saw in the last experiment how

where other forms of power were impractical.

bifacial solar cells are able to collect the solar

Figure 10-36 shows a road sign in the English

energy reflected from two faces. Therefore, in the

countryside, the black sign above is an illuminated

covered walkway they can collect energy reflected

display, which lights up when drivers go too fast.

from the ground (albedo) as well as from direct

It is lit by power produced during the day from a

radiation.

solar cell and also from a micro wind turbine at

99

day or night. The power is stored locally in

batteries located in the foundation of the sign.

In addition to powering devices in remote loca-

tions with no access to the power grid, we can also

construct large photovoltaic arrays, which generate

a significant quantity of electricity which can be

“fed into” the grid when it is not being used on-

site. The great thing about photovoltaic cells, is

that they can be used in place of things like roof

tiles and shingles—so although we cover the building

with photovoltaic cells, which are expensive, we

save on the cost of the roofing material.

We can see how a solar array can be made plain

Figure 10-35

The HEESI satellite powered by solar

and large as in this solar array at the Centre for

power. Image courtesy NASA.

Alternative Technology, U.K. (Figure 10-37).

Or with a little bit of thought, they can be

integrated creatively into the building fabric as

shown in Figure 10-38.

What does it take to

solar power my home?

Producing electricity by photovoltaic cells is fairly

expensive compared to other types of generation.

However, when considering the “cost” of solar

energy, figure in all of the carbon emissions that

you aren’t producing, and the toxic waste that you

aren’t making.

We now know that solar cells can be used to

generate electricity, but the problem is getting it in

a form that we can use in our homes. Sure, it is

possible to run a few simple bulbs from a DC

supply, but to run most of our household appliances,

we need to generate electricity in a form that is

suitable for them—AC.

You will notice that the output from all of our

solar cells is “direct current” (see Figure 10-39).

The voltage is always a fixed polarity with reference

Figure 10-36

A road sign powered by renewable

to 0 V. We can couple solar cells in series to

energy.

produce a higher voltage, or in parallel to produce

Solar Power for Your Home

100

Solar Power for Your Home

Figure 10-37

The 11 kW solar array at the Centre for Alternative Technology, U.K.

Figure 10-38

Photovoltaic cells creatively integrated into a building fabric. Image courtesy Jason Hawkes.

101

Figure 10-39

Direct current.

Figure 10-40

Alternating current.

a higher current, but we are always going to end

into “AC high voltage”? The answer is that we use

up with DC.

an “inverter.”

By contrast, in our homes, our appliances and

An inverter is a piece of electronics (Figure 10-41),

devices require “alternating current,” AC (Figure

which takes the DC supply from our solar cell

10-40). We see how the AC waveform differs

and generates an AC waveform at the correct

dramatically from the steady DC line. In the

voltage and frequency for our items of mains

United States, the frequency of this AC supply is

equipment.

60 Hz, in the U.K. it is 50 Hz, it is also at a higher

We need some extra devices for safety reasons,

voltage (120 V in the U.S.A., and 230 V in the U.K.).

you will see in the setup that there is a mains

So, how can we take the power from our photo-

isolator switch (as shown in Figure 10-42). This

voltaic cells, and turn it from “DC low voltage”

allows us to disconnect the mains from the inverter

Solar Power for Your Home Figure 10-41 A typical inverter setup.

102

Solar Power for Your Home

Figure 10-42

Mains isolator switch.

Figure 10-43

Mains circuit breaker.

in the event that we need to carry out work or

maintenance.

We also need to include a mains circuit breaker

to protect against overcurrents or surges, which

could be potentially damaging and dangerous.

A circuit breaker is shown in Figure 10-43.

And in addition, we need to be able to isolate

the DC supply coming from our solar array. A DC

isolator switch is shown in Figure 10-44.

It is also interesting to see how much energy our

solar array is producing. This can be useful for

accounting purposes, say if we are selling the solar

energy back to the grid, or simply to benchmark

the performance of our solar system and see if it is

in line with our design predictions. A watt hour

meter is shown in Figure 10-45.

Figure 10-44

Solar DC isolator switch.

103

Figure 10-45

Watt hour meter.

Figure 10-46

Awelamentawe school solar display.

Image courtesy Dulas .

Of course, if we have a solar array in a public

prominently mounted in the main reception, to

area, it is also nice to promote solar technology to

show visitors, and help educate children about,

others, and our solar array is a powerful tool to

how much energy the school’s solar array is

educate others with. At this school in Wales, in

producing.

Awelamentawe (Figure 10-46), a display is

Solar Power for Your Home

104

Chapter 11

Photochemical Solar Cells

My sincerest thanks to Dr. Greg P. Smestad for the

information and images he has provided, on which

Note

this chapter is based.

In addition to the photovoltaic solar cells that

The photochemical solar cell is sometimes also

we have seen earlier in this book, there are other

referred to as the “Grätzel” cell after Michael

ways of generating electricity directly from the

Grätzel who worked on developing the cell.

sun. We saw how photovoltaic solar cells rely on

the photovoltaic effect that occurs at semiconductor

junctions, and how the semiconductor performs the

The photochemical solar cell has grown out of

two jobs of absorbing the light and separating

an expanding branch of technology—biomimickry,

electrons.

looking at how we can mimic natural processes to

make more advanced technologies.

One of the problems with this approach is that,

Rather than having a single thing to do all of the

because of the sensitive nature of the cells, they

jobs, as in a conventional photovoltaic cell,

must be manufactured in ultra-clean conditions in

photochemical solar cells mimic processes that

order to be clean and free from defects which

occur in nature.

might impede their operation.

Electron transfer is the foundation for all life in

This works effectively; however, it is expensive.

cells; it occurs in the mitochondria, the powerhouses

The thing about photochemical solar cells is

of cells which convert nutrients into energy.

that they use cheap technology. Titanium dioxide

Titanium dioxide, while not immediately

is not some rare chemical that requires expensive

springing to mind as a household name, is

processing, it is already produced in large quanti-

incorporated in a lot of the products that we use

ties and used commonly; furthermore, you don’t

every day. In paints, as a pigment, it is known by

need an awful lot of it—only around 10 g per

its name titanium white. It is also used in products

square meter. When you figure that this 10 g only

such as toothpaste and sunscreen. Titanium dioxide

costs two cents, you begin to realize that this is a

is great at absorbing ultraviolet light.

solar technology with a lot of promise for the

future.

In an attempt to make solar technology cheaper

Tip

and more accessible, Michael Grätzel and Brian

O’Regan from the Swiss Federal Institute of

You might find titanium dioxide referred to as

Technology decided to explore different approaches

“Titania” in some references.

to the problem.

105

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

process into electrical energy, which travels

How do photochemical

through the circuit to the motor, where electro-

magnets turn the electrical energy into movement

solar cells work?

(kinetic energy).

We need to look at the cell in a little more

Take a peek at Figure 11-1, in the top image, we

depth to understand the chemical processes that

can see the energy transfers taking place—the

are taking place in it in order to generate the

light striking our photochemical solar cell,

electricity.

generating energy and turning the shaft of the

electric motor, which is connected to our cell.

The dye when it is excited by light injects an

The radiated energy from the sun in the form of

electron into the titanium dioxide with which the

light, is being transformed through a chemical

plates are coated and semiconducts.

Photochemical Solar Cells Figure 11-1 How a photochemical solar cell works. Image courtesy Greg P. Smestad.

106

Project 29: Build a Photochemical Solar Cell

Project 29: Build Your Own Photochemical Solar Cell

Online resources

Point your browser toward

www.solideas.com/solrcell/cellkit.html

for more information on dye sensitized

photochemical solar cells and where you can

obtain a kit of the parts featured in this project.

You will need

●

Berries

●

Motor

●

Alligator clips

Figure 11-2

Grinding the nanocrystalline titanium

●

Wires

dioxide. Image courtesy Greg P. Smestad.

●

Nanocrystalline TiO Degussa P25 powder in

2

mortar and pestle

The next thing that we need to do is sinter the

●

Glass plates

titanium dioxide film in order to reduce its

resistivity. This is shown in Figure 11-4. To do

this, we hold it in a Bunsen flame and allow the

Tools

gas to do the work! We need to hold the plate at

the tip of the flame where the temperature is

●

Petri dishes

approximately 450°C or 842°F.

●

Tweezers

Hold it steady for around 10–15 minutes.

●

Pipette

Now you need to produce the dye which will

●

Pencil

sensitize our photochemical solar cell. There are

We need to get our titanium dioxide ground

down so that the particles are as small as possi-

ble—this maximizes surface area, and so allows

our reactions to take place quickly. To do this,

we will need the mortar and pestle mentioned

in our “tools” list (Figure 11-2). Be careful not

to inhale any of the fine titanium dioxide powder

as you are grinding, as it won’t do you any good!

Now that we have prepared our suspension of

titanium dioxide, we need to coat it onto our glass

Figure 11-3

Using a glass rod to spread the suspension

plate using a glass rod. This is shown in Figure 11-3.

onto the plate. Image courtesy Greg P. Smestad.

107

Figure 11-4

Firing the film of titanium dioxide in

Figure 11-5

Coating the plate in berry juice. Image

order to sinter it. Image courtesy Greg P. Smestad.

courtesy Greg P. Smestad.

a number of suggestions for different substances

a voltmeter or continuity tester. The conductive

which can be used for this cell. You can try:

side is the one which yields a positive reading

●

Blackberries

when tested for continuity.

●

Raspberries

We now need to deposit a layer of graphite. The

easiest way to do this is take a soft pencil, and

●

Pomegranate seeds

simply scribble on the surface until a nice even

●

Red hibiscus tea in a few ml of water

coating of graphite is obtained. This is shown in

To produce the dye, you need to take the substance

Figure 11-6. Just note that you need to do this with

you are going to make the dye from, and crush it in a

a plain pencil not a colored one!

small saucer or dish. Once this has been done and a

Now if you have got this far, you are on the

nice fluid has been produced, take the plate which

home run! The next thing we need to do is take

has been coated in titanium dioxide, and immerse it

some of the iodine/iodide mixture, and spread a

in the dye. The titanium dioxide film should now be

few drops evenly on the plate that was stained with

stained a deep red to purple color and the color

the dye (Figure 11-7). Once you have done this,

distribution should be nice and even. If this is not the

case, you can immerse the plate in the dye again.

Once you have finished staining the plate, take a little

ethanol and wash the film and then with a tissue, blot

the plate dry. This is illustrated in Figure 11-5.

Now we need to prepare the other electrode. To

do this you will need another of the coated glass

plates (the one with the conductive tin oxide

coating—not the one with a titanium dioxide

coating). You need to find which is the conductive

surface. There are two ways of doing this—the

tactile method is to simply rub the plate. It should

Figure 11-6

Applying a graphite film to one electrode.

Project 29: Build a Photochemical Solar Cell feel rougher on the coated side. The other involves Image courtesy Greg P. Smestad.

108

Project 29: Build a Photochemical Solar Cell

Figure 11-7

Applying the iodine/iodide mixture. Image

Figure 11-9

The cell yields 6.0 mA. Image courtesy

courtesy Greg P. Smestad.

Greg P. Smestad.

take the other electrode and place it on top of the

Another educational idea is to use a multimeter

dyed electrode. Stagger the junction between the

to measure the amount of power from both a

two plates in order that you leave a little of each

photovoltaic solar cell, and the photochemical

exposed at either end—you can then use a couple of

solar cell you have made, and compare the

crocodile clips to connect the cell to a multimeter.

results—now work out their relative efficiencies

Now clip the sheets of glass together carefully to

taking into account the area of the cells.

ensure they stay together (Figure 11-8).

Now we can take some measurements! Figure 11-9

Now connect a multimeter—we can start to

shows a photochemical cell yielding 6.0 mA!

think about doing some really cool stuff now! You

Apparently, the juice in this picture is from

might like to try a few different experiments—like

Californian blackberries!

seeing what way to shine the light through the cell

Figure 11-10 shows a photochemical cell being

for the most effective operation. You might like to

used to drive a small motor and fan.

repeat some of the experiments in the section on

photovoltaic solar cells, and see what results you

obtain with a photochemical solar cell.

Figure 11-8

Clipping the cell together with bulldog

Figure 11-10

The cell driving a small motor. Image

clips. Image courtesy Greg P. Smestad.

courtesy Greg P. Smestad.

109

When you consider all of the glazing that adorns

the skyscrapers in our cities, you begin to realize

that this technology has interesting applications

for energy generation. It also allows us to make

good use of daylight with our south-facing

building areas, while generating energy at the

same time.

There are also implications for consumer electron-

ics, the watch giant Swatch has already built a

prototype watch with a photochemical cover glass.

This allows the glass which covers the watch to

Figure 11-11

A closeup of the photochemical cell in

generate electricity all the time the watch is

action. Image courtesy Greg P. Smestad.

exposed to light. When you think that people wear

watches on their wrists where they are permanently

Figure 11-11 shows a close-up of the cell

exposed to daylight, this becomes quite a sound

working in action!

idea! Of course, you also need some means of

storing the electricity to enable the watch to run

at night! It would be no good to wake up, put on

your watch, only to find the time is set to the

Online resources

evening before.

The materials required for this project are

available from the Institute of Chemical

Are there any limitations

Education from the following link or the address

in the Supplier’s Index: ice.chem.wisc.edu/

to this technology?

catalogitems/ScienceKits.htm#SolarCell

One of the problems with this particular type of

cell is that the cell contains liquid which is

essential for its function. Unfortunately, liquid is

Where does it all go from

hard to seal and keep in—preventing the liquid

here?

from leaking is a real technical issue that needs to

be solved. After all, you wouldn’t want leaky

This technology has a lot of promise for the future.

windows! If you have ever seen a poorly fitted

There is a growing trend for manufacturers to inte-

double glazing panel with condensation inside,

grate renewable energy systems into building ele-

you realize how hard it is to seal building

ments—this allows us to feed two birds with one

fixtures and fittings against the ingress or egress

crumb, rather than shelling out for roof tiles and

of fluid.

solar cells, why not buy a solar roof tile! The excit-

However, there is hope on the horizon, Grätzel

ing thing about photochemical solar cells is that

together with the Hoescht Research & Technology

unlike photovoltaic cells, they don’t necessarily

in Frankfurt, Germany, and the Max Planck Institute

have to be opaque. This opens up exciting possi-

for Polymer Research in Mainz, Germany, have

bilities—shaded windows and skylights which

announced that they have developed a version of

simultaneously produce electricity. How cool

the cell with a solid electrolyte; however, efficien-

would that be!

cies are low.

Project 29: Build a Photochemical Solar Cell

110

Photobiological Solar Cells

Arizona State University have initiated a project

Photobiological solar

codenamed Project Ingenhousz which is looking

cells?

at photosynthesis and how organisms can be used

to harness solar energy to produce fuels that will

Truth can sometimes be stranger than fiction.

wean us away from our carbon-based fossil fuels.

Realizing that conventional solar cells require

Could your car one day run from hydrogen that

expensive industrial processes, researchers at

has been produced by algae from solar energy?

111

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Chapter 12

Solar Engines

In this book so far, we have seen how it is pos-

steam condenses back to water can also be used to

sible to utilize the energy that comes from the

provide movement.

sun in order to do some really useful things. While

If you want proof of this, take a soda can with a

generating heat and electricity is useful to help us

little bit of water in the bottom. Heat it on the

reduce our energy consumption, it would also be

stove until you see a little wisp of water vapor

useful if we could use the sun’s energy to create

come from the can—this is evidence of the water

mechanical movement. Mechanical movement is

having boiled. Now, using tongs, flip the can over,

very useful and can be directly utilized to drive

and immerse the “top” of the can in a bowl of ice

machinery.

cold water. The can is instantly crushed!

When we look at the type of energy coming

So now we have evidence that a change in

from the sun, we can see that it is heat and light—

temperature can produce movement, we can look

the energy is transmitted by radiation through the

at how to harness this raw power.

vacuum of space.

The engines described in this chapter, are all

How therefore, do we exploit this radiated

examples of thermodynamic heat engines. The

energy and convert it into mechanical motion?

chapter will showcase a few simple solar engines

You must be familiar with the steam engines that

that you can construct yourself with relatively

once graced railways throughout the world. The

simple materials.

steam engine is a form of indirect combustion

All of the engines in this chapter produce a

engine, the coal is burned to heat water, which

fairly modest amount of mechanical power, but all

undergoes a phase change—the water turns from

serve to demonstrate that solar energy does have

liquid to gas. In doing so, it increases in volume—

application in directly driving mechanical devices.

what once took up a small space, now takes up a

large space—this change can be exploited to

I gratefully acknowledge the advice and

provide mechanical movement by driving a piston.

guidance of Hubert Stierhof in the preparation of a

Furthermore, the change in volume when hot

number of projects in this chapter.

Project 30: Build a Solar Bird Engine

You will need

Tools

●

Happy Drinking Bird (won’t be so happy when we

●

Scalpel

are finished!)

●

Kettle

●

Silver spray paint

We are going to have to “kill a bird” to execute

●

Black spray paint

this project—luckily the bird in question is

113

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Figure 12-2

The Drinking Bird in action.

Warning

The liquid which fills the Drinking Bird is known

as dichloromethane. This chemical is pretty nasty

stuff—safe while trapped in the glass of the

Figure 12-1

The Drinking Bird in its box.

drinking bird’s body, but nasty if it escapes—so

exercise caution, and try not to break or damage

the bird in any way.

a cheap toy from the Far East, so our consciences

The liquid inside the bird (dichloromethane)

are clear!

condenses readily with only a small temperature

The “Happy Bird,” “Happy Drinking Bird,”

difference. In the normal mode of operation, you

“Drinking Bird,” “Tippy Bird,” “Sippy Bird,”

start the bird by “dunking” its head in a small glass

“Dippy Bird” or any one of a number of ridiculous

of water, and then allowing it to stand. What

names is a cheap novelty toy (Figure 12-1). It is

happens when you do this, is that water begins to

also a serious scientific curiosity!

evaporate from the bird’s head. As it does so, it

First of all a little note, don’t jump straight into

takes heat with it, cooling the bird’s head, relative

massacring the bird—have a little play with it,

to the ambient temperature, which the “bottom”

because it is a lot easier to see what is going on

bulb is at.

before you hack it (Figure 12-2).

As the top is cooled, the dichloromethane gas in

the head begins to condense creating a drop in

How the Drinking Bird works

pressure. The liquid from the bottom bulb now

begins to flow into the head bulb.

The Drinking Bird contains a pair of glass bulbs,

As the liquid moves through the central tube,

joined by a glass tube, attached to which is a pivot.

the weight distribution of the liquid in the bird

The pivot rests on top of the “legs” of the bird, and

changes. The bird now becomes “top heavy” and

in the normal position, one bulb (the tail) will be

as a result of this, the bird rotates on its pivot. This

full of liquid, while the other bulb (the head) will

movement is the useful “work” which the heat

Project 30: Build a Solar Bird Engine be empty.

engine is doing.

114

Project 30: Build a Solar Bird Engine

As the bird tips over, the seal between the “neck”

tube, and the surface of the dichloromethane is

broken. A small bubble of vapor flows through the

neck tubes. As it does so, it displaces liquid, which

begins to flow back down to the tail bulb. As the

liquid flows back from top to bottom, the vapor

pressure equalizes and the bird “rights itself.”

As the liquid flows back into the bottom bulb,

Figure 12-3

The drinking bird stripped bare.

the weight distribution again changes, and the bird

pivots back to its vertical position. Again, more

nose from the head. With a sharp scalpel, you can

useful “work” is done here.

cut through the plastic backing of the felt, and

The cycle keeps repeating itself until the water

using hot water, you can scrape all the glue and

in the pot runs out. The process is driven by the

gunk off. You should now be left with a nice clean

heat in the environment which causes the water to

piece of glassware.

evaporate. The dichloromethane is not “used up” in

Now, remember that the device works on the

any way—it is the working fluid of the engine and

principle of temperature difference. You will

stays trapped inside the drinking bird.

remember from experiments earlier in the book,

We are going to change the Drinking Bird, so

that black surfaces absorb solar radiation, while

that instead of being driven by the temperature

shiny or reflective light surfaces reflect solar

difference caused by water evaporating, it will

energy. A black car feels hotter than the silver one

instead be driven by the temperature difference

created by surfaces that absorb and reflect the

sun’s rays.

How we are going to “hack” it . . .

We don’t want to have to keep replacing our water

in order to keep the bird working.

Now is the fun part, if you are of a destructive

disposition.

We are going to take all of the little accou-

trements away from this beasty! Boil a kettle and

get some hot water, you will find it softens the

glue and makes it a lot easier to remove things.

Remember, the glass is only thin and easy to

break.

Pull the hat of the bird. The hat usually disguises

a little glass protrusion on the top of the bulb

(Figures 12-3 and 12-4), so do this carefully, if you

break the envelope of the bird it stops working.

Also, the little tail feather is going to need to go.

Figure 12-4

The “hacked” drinking bird with it's

Next you are going to have to remove the felt and

fresh new paint scheme.

115

next to it! So, get some spray paint—the type used

“base” of the bird is going to heat up as it absorbs

for touching in dents on cars works well—and

solar radiation.

spray the bottom bulb black and the top one silver.

Now position the “solar engine” back on the legs

Remember the evaporation of water cooling the

of the bird, and put it somewhere where it will

“head” of the bird. Well, instead, reflective silver

receive a lot of sunlight. You should now see the

paint is going to keep the head cool. The black

engine tipping away without the need for any water!

Project 31: Make a Radial Solar Can Engine

result of the black covering absorbing the sun’s

You will need

rays. This increase in temperature results in the air

inside the can expanding slightly. This increase in

●

Polystyrene ceiling tile or sheet polystyrene

volume exerts a force on the rubber diaphragm

●

Three old cans

covering the can. The diaphragm is connected to a

●

Stiff wire (coat hanger wire is ideal)

short rod, which pushes against the crank turning

●

Three balloons

the can assembly. When the can has rotated far

enough so that it is covered by the polystyrene shade,

●

Wooden strut

then the sun’s rays can no longer reach the can. As

a result, the air inside the can begins to cool down.

Tools

As the air cools, it contracts, in doing so, it pulls

the rubber diaphragm (Figures 12-5 to 12-12).

●

Tin opener

●

Scissors

●

Wire snips

You might remember the biplane engines of old—

they had their pistons arranged around a centrally

driven shaft—the prop shaft—which would turn

the propeller. This is known as a radial engine.

In our cars, the pistons are generally arranged in

a straight line or sometimes a “V,” radial engines

are different in this respect.

In this project, we will be building a radial

engine, only rather than being fueled by aviation

fuel, our engine is powered by the sun!

How does the solar radial engine

work?

The cans that are exposed to the sun (i.e. not

Project 31: Make a Radial Solar Can Engine covered by the polystyrene shield) heat up as a Figure 12-5

Solar radial can engine.

116

Project 31: Make a Radial Solar Can Engine

Figure 12-6

The polystyrene shade.

Figure 12-9

The can assembly on its stand (from

above).

Figure 12-7

The view from behind the can engine.

Figure 12-10

The can assembly on its stand (from

Figure 12-8

The can assembly (note the crank

the side).

detail!).

117

Figure 12-12

Diagram of the radial can engine.

Figure 12-11

Note carefully how the crank is

configured.

Project 31: Make a Radial Solar Can Engine

118

Chapter 13

Solar Electrical Projects

In this chapter, we cover a number of small

how many common household devices that we

electronic projects you can build that are powered

take for granted could potentially run successfully

by solar energy. The chapter aims to show you

on solar energy.

Project 32: Build Your Own Solar Battery Charger

This circuit is a very simple design which doesn’t

You will need

provide any regulation, so you will need to make

sure that you disconnect your batteries when they

●

AA battery holder

are recharged.

●

9 V battery clip (you might need this to connect to

The Schottky diode prevents the batteries’ charge

your battery holder)

from flowing back through the solar cells when no

●

8 × solar cells 0.5V, 20 to 50 mA in full sun

charge is present. Schottky diodes have the advan-

●

1N5818 Schottky diode

tage of not sapping too much of the power from

Rechargeable batteries make good economic and

our solar cells—maximizing the amount that is

environmental sense. In the same way that you

delivered to the batteries.

wouldn’t throw away the glass every time you had

The schematic for the battery charger is shown

a drink, so it doesn’t make sense to dispose of

in Figure 13-2.

batteries when others are available that perform the

same task many times over.

It gets even better than that when you realize

Hint

that you don’t have to use any mains electricity at

all to recharge your batteries—you can use the

If you live in a climate where sun is a rare treat

power of the sun!

and it is often overcast, you might like to

Solar battery chargers like this model are

experiment with a couple of additional cells in

series to increase the power produced.

commercially available, which can be obtained

from the Centre for Alternative Technology, U.K.

(see Supplier’s Index) (Figure 13-1); however, if

Construction is fairly simple. There are a wide

you are electronically minded you can easily put

array of cases available that are suitable for

one together.

housing such a project. If you can get a housing

The circuit here will recharge a pair of AA

with an integral battery holder you will find it will

batteries quite happily when left in the sun.

make neat work of housing the project.

119

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Tip

House the cells in such a manner that they are

shaded and protected from the sun. If the cells get

too hot their electrolyte leaks—damaging the cell

and making a mess.

If you want to build a “deluxe” model, you

might want to consider incorporating a small

milliammeter to monitor the charging status.

Figure 13-1

Commercially available solar battery

charger.

Figure 13-2

Solar battery charger schematic.

Project 33: Build Your Own Solar Phone Charger

You will need

Or for the USB version:

●

100 µF capacitor

●

Car charger suitable for your cell phone (for

cannibalization)

●

100 pF capacitor

●

7812 voltage regulator

●

1 mH inductor

Project 33: Build Your Own Solar Phone Charger ● 15 V solar array

●

1N5819 diode

120

Project 33: Build Your Own Solar Phone Charger

In this project, we are going to build a circuit

that will provide a supply capable of powering

either a cellphone or PDA charger. A PDA is about

the limit of what you can charge using small cells,

a laptop charger is probably a bit ambitious.

One of the problems with trying to build this

circuit is that finding a suitable connector for

many mobile phones is a real problem. While

Nokia makes life easy by providing a simple jack

that can be readily obtained from many component

suppliers, many other manufacturers rely on

proprietary connectors which are nonstandard

and awkward to source.

For this reason, we have based this project on

hacking a cellphone car charger.

There are two schematics here for projects that

tackle the project from slightly different angles.

The first method involves creating a solar array

that will provide above 12 V—regulating this

supply to 12 V, and charging the device via a

hacked “car charger” (Figure 13-4). The other

device is suitable for where a USB type charger is

available—this is ideal for USB mp3 players,

Figure 13-3

A solar-powered phone—albeit not all

PDAs and mobile phones, most of which now

that portable.

come with a “data” lead. We have an array of

solar cells, which charges a couple of batteries

when there is spare power; a voltage regulator then

●

274 k resistor (1% tolerance)

turns this into a clean 5 V, which can be used to

●

100 k resistor (1% tolerance)

drive the device (Figure 13-5). The advantage of

●

100 µF capacitor

this circuit is that even if there is not a lot of sun—

●

USB socket

or it is night-time, you can pop a couple of freshly

charged batteries in (maybe from your solar

●

MAX 630 CPA integrated circuit

charger?) and things will start working.

It’s the same old story—just when you want to talk

on your cellphone, the battery goes flat and the

Car chargers are designed to allow you to plug

conversation is irretrievably lost! Invariably, you

your phone into your vehicle’s cigarette lighter or

haven’t got your phone charger on you, and even

accessory socket. They are cheap and readily

if you did have it wouldn’t be an awful lot of help

available; however, they rely on having a car

as the chances are there is no power for miles

present to allow you to charge your phone!

around . . .

There are a couple of ways of making this pro-

At the Centre for Alternative Technology, U.K.,

ject. You can either build the project as a box into

there is a solar-powered phone (see Figure 13-3);

which you plug your car cellphone charger,

while this is powered by clean green energy, it

or, if you are a little more adventurous, you can

can’t claim to be very portable!

take apart the cellphone charger and integrate it

121

properly into the box. The plus side of keeping

the two pieces separate is that you can use the car

Note

cellphone charger as a stand-alone item, or, you

can power it from the “solar box.” The plus side of

A note on cigarette lighter sockets—the usual

integrating it all together is that it makes for a neat,

wiring scheme is that the casing of one of these

stand-alone project and the two parts cannot become

sockets is connected to the negative terminal of

separated.

the battery

Figure 13-4

Solar-powered phone charger schematic: car charger.

Figure 13-5

Solar-powered phone charger schematic: USB type.

Project 33: Build Your Own Solar Phone Charger

122

Project 34: Build Your Own Solar-Powered Radio

Project 34: Build Your Own Solar-Powered Radio

A solar radio is another great idea! Never mind

You will need

“Desert Island Discs,” with a solar radio, you can

ensure that if you are ever marooned, you are able

●

Ferrite rod antenna

to listen to your favorite radio stations!

●

60–160 pF variable capacitor

In this circuit we are going to build a simple AM

●

BC183 transistor

radio that is powered by the sun.

●

10 nF capacitor

There are some commercially available radios

●

0.1 mF capacitor × 2

powered by solar energy; however, it is relatively

●

470 µF capacitor

easy to build your own. We are basing this circuit

around the MK484 integrated circuit, which takes

●

220 R resistor

all the hassle out of building a simple radio. The

●

1 k resistor

integrated circuit looks like a transistor with three

●

100 k resistor × 2

pins, and reduces the amount of external compo-

●

10 k potentiometer

nents needed considerably.

●

Speaker

The schematic for the circuit is shown in

●

PV cell

Figure 13-6.

●

PCB stripboard

The radio has two controls. The variable capacitor

changes the frequency that you are tuned to, and

Tools

the potentiometer acts as a volume control for the

simple transistor amplifier.

●

Soldering iron

There are a number of commercially available

●

Solder

solar radios; one idea for mounting, which you

Figure 13-6

Solar AM radio schematic.

123

Figure 13-7

Headphone mounted commercial solar

Figure 13-8

“Freeplay” wind-up and solar radio.

radio.

could easily accomplish with the solar radio circuit

two renewable energy sources—solar power, and

above, is to mount the circuit in a set of head-

for less sunny days “human wind-up power” in

phones, like the solar radio shown in Figure 13-7.

order to make sure that even when the sun doesn’t

The radio in Figure 13-8 is the “Freeplay”

shine, you aren’t without your tunes!

wind-up radio invented by Trevor Bayliss. It uses

Project 35: Build Your Own Solar-Powered Torch

●

10 k 1⁄4 W carbon film resistor

You will need

●

560 R 1⁄4 W carbon film resistor

●

4× 1.5 V solar cells

●

2× 3.3 R 1⁄4 W carbon film resistor

●

1× AA 600 mAh NiCad battery

●

C9013 NPN transistor

●

1N5817 Zener diode

●

C9014 NPN transistor

●

220 k 1⁄4 W carbon film resistor

●

C9015 PNP transistor

●

100 k 1⁄4 W carbon film resistor

●

300 pF ceramic capacitor

●

91 k 1⁄4 W carbon film resistor

●

100 nF ceramic capacitor

Project 35: Build Your Own Solar-Powered Torch

124

Project 35: Build Your Own Solar-Powered Torch

●

1 nF ceramic capacitor

●

82 µH inductor

●

CdS photocell 47 k @ 10 lux

●

2 × LEDs

In lists of made-up useless things, solar-powered

torches seem to come out somewhere at the top.

Figure 13-9

Solar-powered torch.

After all, what use is there for something that

produces light that is powered by light? Until you

realize that we can use batteries to store the

energy—this is a crucial leap in understanding!

Now doesn’t the solar torch seem so much more

interesting?

A solar torch is a useful thing to build and then

leave on a sunny window sill. In the event of a

power cut, you know that you can go to your trusty

solar torch to provide a (somewhat modest)

amount of illumination!

Figures 13-9 and 13-10 show a solar-powered

torch and the solar torch in its packaging. One of

the things you need to think about if you are going

to house your project in a round torch case, is that

you will need to ensure that either:

●

The torch is weighted so that it rolls in such a way

that the solar cell points upwards.

or

●

There is a flat machined into the case, which

ensures that the solar cell points upwards when the

flat in the case rests on a level surface.

Tragedy would strike if your solar torch were to

roll over so that the flat faced away from the

Figure 13-10

Solar-powered torch in its packaging.

ground—blocking sunlight to the solar cell!

The circuit is shown in Figure 13-11. It is a

variation of the outdoor solar light circuit (which

of the photocell. It allows manual control of the

you will see later in this chapter), where a pair of

LEDs and economizes by only using a single

resistors and a switch are used to mimic the action

battery.

125

Figure 13-11

Solar-powered torch schematic.

Project 36: Build Your Own Solar-Powered

Warning Light

Often, the place where you want to position the

You will need

warning light or strobe is totally remote from any

source of power. Although we can often run things

●

Capacitor 0.1 F, 5.5 V

from batteries, sometimes we want to put a light

●

Capacitor 100 µF

where changing a battery would be undesirable.

●

Capacitor 6.8 µF

Solar energy, as well as producing clean renewable

●

2 × resistors 100 k

energy, also allows us to power things in remote

places that would not easily be accessible using

●

2 × resistors 100 ohms

conventional cables, or where changing a battery

●

PNP transistor

could present a problem.

●

NPN transistor

In Figure 13-12 we see a commercially available

●

2 × diodes 1N4148

solar waterproof warning light, there are many

●

Super-high brightness red LED

applications for this—you might want to strap it to

●

100 µH inductor

your back while cycling, for instance.

●

4 × small solar cells

The beacon has a couple of modes. When the

beacon is set to off, the solar cell will charge the

battery; however, the light will not flash under any

Tools

circumstances. In “solar” mode, the beacon will

charge during the day, and when the circuit senses

●

Soldering iron

a low lighting condition, the beacon will begin to

There are many applications where it is useful to

flash using the power stored in the rechargeable

Project 36: Solar-Powered Warning Light have some sort of warning light, strobe, or beacon.

battery. Set to “on” the beacon will flash regardless

126

Project 37: Build Your Own Solar-Powered Garden Light

of whether it is light or dark—however, bear in

mind that this will drain the battery.

If you are going to use this beacon outside all of

the time, you might want to think about how you

can protect the circuit (Figure 13-13) against the

ingress of water and solid matter. Most suppliers

of cases sell a range of decent waterproof cases

that are eminently suitable for outdoor use, or

you may find that you can improvise with a

Tupperware or similar container to produce a

satisfactory housing.

Figure 13-12

Solar waterproof warning light.

Figure 13-13

Solar waterproof warning light schematic.

Project 37: Build Your Own Solar-Powered Garden Light

●

2 × 3.3 R 1⁄4 W carbon film resistor

You will need

●

C9013 NPN transistor

●

4 × 1.5 V solar cells

●

C9014 NPN transistor

●

1 × AA 600 mAh NiCad battery

●

C9015 PNP transistor

●

1N5817 Zener diode

●

300 pF ceramic capacitor

●

220 k 1⁄4 W carbon film resistor

●

100 nF ceramic capacitor

●

100 k 1⁄4 W carbon film resistor

●

1 nF ceramic capacitor

●

91 k 1⁄4 W carbon film resistor

●

82 µH inductor

●

10 k 1⁄4 W carbon film resistor

●

CdS photocell 47 k @ 10 lux

●

560 R 1⁄4 W carbon film resistor

●

2 × LEDs

127

Tools

●

Soldering iron

Solar-powered path lights (Figure 13-14) are

becoming ubiquitous in just about every garden

center nowadays! There are lots of advantages to

using solar power rather than a hard-wired system.

First of all, as a hard-wired system is exposed to

the elements, you need to ensure that you use

low-voltage fixtures and fittings, which require

a transformer to step down the voltage, or failing

that, really expensive mains fixtures and fittings.

Then the next thing to consider is that even the

safest low-voltage system is still vulnerable to the

gardener’s spade—a badly placed spade can mean

disconnection of your garden lighting system.

Solar-powered garden lights have none of these

disadvantages. They charge their batteries during

the day, and then at night as the light fades, they

switch on, providing illumination.

Figure 13-14

The change in illumination is detected by a CdS

Solar garden light.

photocell.

We will be using LEDs for this project (Figure

13-15) as they provide good efficiency—a decent

amount of illumination for the relatively small

amount of energy we are able to provide.

Figure 13-15

Solar garden light schematic.

Project 37: Build Your Own Solar-Powered Garden Light

128

Chapter 14

Tracking the Sun

One school of thought advocates positioning your

One of the main caveats of this design is that

solar panels on a fixed surface such as a roof,

moving the panels does require some input of

positioned so as to harness as much sun as possible

energy, and this must of course be subtracted

on average over the year. This approach certainly

from the total energy that the panels are

works, but as we saw in Chapter 3, the sun is not a

producing.

fixed object in the sky—it moves, and so this

Furthermore, in some scenarios this is inappro-

approach is not necessarily the best.

priate—if you are roof-mounting panels, it would

One other solution is to actively track the sun

not really be appropriate to “reposition your roof”

using a device such as the trackers shown in

every time the sun moves.

Figures 14-1 and 14-2. What this entails is using

In this chapter we will build a circuit that can be

motors, hydraulic actuators, or some other devices

used to track the sun’s movements and move a

to move our solar panels to follow the sun. This

solar panel accordingly. The circuit is only

approach does have some merits. With the sun

simple, and will power a small motor to drive a

always facing the panels as face-on as possible, the

demonstration display; however, with correct

most possible energy is extracted, as the panels are

driver circuitry, the circuit could easily be scaled

operating at their greatest efficiency.

up to move bigger arrays.

Figure 14-1

Solar tracker at Llanrwst, near Snowdonia, Wales. Image courtesy Dulas Ltd.

129

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Figure 14-2

Solar tracker at Llanrwst, near Snowdonia, Wales. Image courtesy Dulas Ltd.

Tip

If you don’t fancy building your own solar tracker

from scratch, Science Connection sells one as a

kit under the stock code number 2216KIT. Full

details are in the Supplier’s Index.

www.scienceconnection.com/Tech_advanced.htm

Project 38: Simple Solar Tracker

●

10 k variable resistor

You will need

●

20 k variable resistor

●

3 × LDR

●

2N4401 transistor

●

33 R resistor

●

TIP120 Darlington pair

●

75 R resistor

●

9 V relay

Project 38: Simple Solar Tracker ● 100 R variable resistor

●

5 V motor

130

Project 38: Simple Solar Tracker

How the circuit works

We have three CdS photoresistors (Figure 14.3)

The value of these resistors is about 5 k when not

exposed to light. However, when we expose them

to light their resistance decreases to around about a

couple of hundred ohms.

The third CdS cell is mounted in a shrouded

enclosure so that it is only illuminated when it

faces directly toward the sun. When the sun illumi-

nates this photocell, its resistance drops, and as a

result, when the sun shines on it, our Darlington

pair is kept off.

When the sun moves away from the line of sight

of photoresistor 3, its resistance increases. This

allows our Darlington pair to switch on, which in

turn drives our relay, which in turn drives our

motor to move the array.

Figure 14-3

Simple solar tracker schematic.

The variable resistor in line with the relay and

motor allows us to regulate the motor’s speed. The

disappears behind a cloud its resistance rises and

motor should turn slowly enough to move the

our NPN transistor base is allowed to be high, this

array, but not so fast that the array overshoots

in turn drives the base of our Darlington pair low,

before photoresistor 3 has a chance to respond to

which prevents the tracker from tracking.

the change.

Photoresistor 2 is mounted flush with the panel

Our first photoresistor is mounted on the back of

so that it can see the whole sky. Its function is to

our tracker. It senses the new light coming from

check that the sun is present, to prevent the array

the east and activates the turntable to allow our

from searching for a sun that isn’t there! If the sun

solar panels to face the sun to catch the new light.

is present it will sense this and drive the base of

The setup for our solar array and sensors is

our NPN transistor low. However, if the sun

illustrated in Figure 14-4.

Hint

Tip

If you want to adjust the sensitivity of a CdS

photoresistor without fiddling with the

Poulek Solar, Ltd., whose website is www.solar-

electronics, you can decrease its sensitivity to

trackers.com sell commercially produced solar

light by drawing on a section of the sensing

tracking circuits and all of the hardware to mount

element with a black permanent marker. This

your panels on a sturdy outdoor tracker. See

prevents some light reaching the sensor.

Supplier’s Index.

131

Figure 14-4

Solar array and sensors setup.

Taking it further

Solar trackers in the

real world

You don’t have to use this simple circuit just to

move a solar panel, you can think of ways to move

Now we have built a model, let’s take a look at a

any of the solar projects presented in this book.

real solar tracker and gain some insight as to the

You might want to move a solar cooker for example.

capabilities of the technology.

The motor used in the circuit might only be small;

however, you can use gearing to enable it to move

larger loads. We only want slow motion from our

motor anyway, so slow movement is ideal.

Mr Howie, Scotland

Here, it was decided that solar trackers were the

way forward, as the roof structure of the house on

Online resources

the property was not strong enough to support a

solar array, and the rafters were irregularly

spaced—making it difficult to install mounting

If you want to explore more sophisticated solar-

hardware. As the property was surrounded by a

tracking devices, here are some links to hobbyists

lot of land, it was decided that it was cogent to

pages which will take you further in your design

install a stand-alone array. As Scotland is at quite

of solar trackers.

a high latitude, it was decided that using a solar

pages.prodigy.net/rich_demartile/

tracker would make the best use of the available

www.redrok.com/electron.htm#tracker

solar resource.

www.phoenixnavigation.com/ptbc/articles/

The array (Figure 14-5) is 1.92 kW peak, and

ptbc55.htm

was 48% funded by an Energy Saving Trust grant.

Project 38: Simple Solar Tracker

132

Solar Trackers in the Real World

Figure 14-5

Solar tracker on the property of Mr Howie, Scotland. Image courtesy Dulas Ltd.

133

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Chapter 15

Solar Transport

is an energy-dense, readily-available (at present)

Why solar transport?

fuel, which provides power-on-demand when we

want it.

The way that we live today necessitates traveling

However, imagine a world without cheap gas-

long distances—whereas historically all travel was

oline . . . How would we get about? As Chapter 1

on foot, we are now assisted by cars, boats, and

mentioned, a world without petroleum may be here

trains to get us from place to place.

sooner than we think.

Our world has shrunk—low-cost air travel

Furthermore, the burning of lots of gasoline and

now means that we can be anywhere in the

diesel results in all sorts of “nasties” going into the

world affordably within the day, and the car

air that you and I breathe—this includes carbon

means that we can travel almost anywhere local

dioxide, oxides of sulfur which are responsible for

by road in a matter of minutes.

acid rain, oxides of nitrogen, particulates, and

Our world today has been styled and shaped by

unburnt hydrocarbons. We are putting this lethal

our transport patterns. Many people live in the

cocktail into our air day-by-day.

suburbs and commute for what would have been

incredibly long distances in the past to get to their

places of work, shops, and amenities.

What are the alternatives?

Where in the past shops were a local affair, now

we go to large sprawling out-of-town shopping

Well, for a start we can try to change our transport

centers and malls.

patterns. Social fixes like this are really cheap

All of this increased transport affords us endless

and necessitate minimal investment. What this

convenience, but what is the real cost?

means in practice is drive less and fly less. It

might sound tough, but in fact it really is easy to

make a conscious effort to reduce our transport

patterns.

The environmental cost of

Also, in addition to trying to reduce the amount

transportation

that we travel, we can try to reduce the amount

that other people have to travel. This could be

The city of Los Angeles in the U.S.A. is an example

done, for example, by sourcing locally produced

of a city that has learnt to pay the price for heavy

products.

use of transportation. The city’s urban planning has

We can try and reduce our carbon emissions by

dictated that people use their own private vehicles,

using public transportation—it follows that it is

as public transportation is poor.

more efficient to move a large number of people

Transportation uses the bulk of the world’s

than a small number of people—the efficiency

petroleum. We use petrol or gas (depending on

gains and economies of scale mean that we save

which side of the pond you come from), because it

fuel and avoid many emissions.

135

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Figure 15-1

Honda dream car. Image courtesy Honda.

However, there must be alternatives to our present

it is possible to produce a vehicle that runs on

fossil fuel-based vehicles, and yes there are. You’ll

solar energy.

never guess what . . . these alternatives are solar

There are a number of competitions that aim to

derived as well! Read on and see what the exciting

spur on the development of solar vehicles, two

technology has in store.

notable competitions are the World Solar Chal-

lenge, and the North American Solar Challenge. If

you are really keen on getting into solar vehicles,

Solar vehicles

some of the top universities enter cars into the

races.

At the moment, solar cars aren’t really practical for

OK . . . so entering a full-size solar car into a

you and I to drive about in—simply too much

race is a little bit pricey (Figure 15-2), but what

surface area is required to mount the solar cells.

can you do instead to fulfill your solar ambitions?

Also, some method of storing the solar energy

Follow the next project and find out how to build a

needs to be employed for when your car goes into

simple solar vehicle!

a tunnel or the sun hides behind a cloud. Even so,

solar vehicles such as the Honda Dream shown in

Figure 15-1 are an interesting demonstration that

Online resources

Take a peek at the World Solar Challenge website

to see what is going on

Online resources

www.wsc.org.au/

Check this website about solar vehicles for some

Also, the North American Solar Challenge is

cool information

here

www.formulasun.org/education/seles9.html/

www.americansolarchallenge.org/

Solar Transport

136

Project 39: Build Your Own Solar Car

Figure 15-2

Solar vehicles lined up for a solar car race. Image courtesy NASA.

Project 39: Build Your Own Solar Car

In this project we will be building a small solar

●

2n3906 transistor

vehicle that demonstrates how solar power can be

●

1381 voltage trigger

used to propel a small vehicle. In the next projects,

●

2.2 k resistor (color bands red/red/red/gold)

you will learn how to “soup up” your racers and

●

SC2433 24 × 33 mm 2.7 V solar cell

race them.

●

Pair solar cell wires

●

25 mm (1 in.) length 18 gauge wire

You will need

Tools

●

SolarSpeeder 1.1 printed circuit board (PCB)

●

High-efficiency coreless motor

●

Soldering iron

●

Motor mounting clip

●

Needle-nose pliers

●

3 × Rubber wheels on nylon hubs

●

Side-cutters or strong scissors

●

43 mm long 1.40 mm diameter (1.7 in. long,

●

File and/or sandpaper

0.055 in. diameter) steel rod

●

Glue, rubber cement, or hot-glue (or superglue, if

●

2 × Black plastic wheel retainers

you’re very careful)

●

0.33 F 2.5 V gold capacitor

●

Safety glasses— very important when clipping and

●

2n3904 transistor

snipping!

137

First, assemble all of the components for the

Solaroller as in Figure 15-3.

Note

When our project is complete, it will look like

A full kit of parts for the following project is

the pretty little bug in Figure 15-4.

available from Solarbotics at

First of all, take a look at the schematic in

www.solarbotics.com

Figure 15-5. This is a pretty standard design for a

solar engine. What is happening here is that our

Figure 15-3

Components of the Solaroller.

Project 39: Build Your Own Solar Car Figure 15-4 The assembled Solaroller. Image courtesy Solarbotics.

138

Project 39: Build Your Own Solar Car

little solar cell is providing electrical energy which

Next, take the high-capacity capacitor, bend the

is charging the high-capacity capacitor. When the

leads so that they are flush with the body of the

voltage reaches a certain threshold level, the 1381

capacitor. Then solder it into the PCB. Ensure that

triggers the output circuit, which dumps the power

you solder this in the correct orientation.

in the capacitor through the motor, creating

Next, take the 2.2 k resistor and solder it as shown.

movement.

The orientation of the resistor is unimportant.

The first step of assembling your Solaroller is

The next stage in assembly is shown in

illustrated in Figure 15-6. You are going to need to

Figure 15-7.

take the axle and thread it through the two holes in

First take the 3904 transistor and solder it at the

the circuit board named “rod.”

head of the board in the orientation shown in

Figure 15-7.

Now the 1381 and 2906 transistors are soldered

in either side of the board facing down. This is also

illustrated in Figure 15-7.

Finally take the small fuse clip which will be

acting as our motor mount and solder it into the

bottom of the board. Note that the fuse clip has a

small lip to prevent the motor sliding out. Ensure

that you orient this correctly.

Now you have got this far you are definitely

Figure 15-5

The Solaroller schematic. Image

cooking with gas! . . . or should that be with solar?

courtesy Solarbotics.

Now take the small high-efficiency motor and

insert it into the fuse clip in the manner shown in

Figure 15-8.

Figure 15-6

Step 1—assembling the Solaroller. Image

Figure 15-7

Step 2—assembling the Solaroller. Image

courtesy Solarbotics.

courtesy Solarbotics.

139

Figure 15-9

Step 4—assembling the Solaroller. Image

courtesy Solarbotics.

Figure 15-8

Step 3—assembling the Solaroller. Image

courtesy Solarbotics.

Adding the wheels at the front is a simple

procedure of pushing them onto the axle and then

adding the small black plastic clips which will

retain the wheels and prevent them from sliding

off. Now take the motor leads which are very deli-

cate so treat them with a lot of respect! The red

one should be soldered into the hole on the PCB,

the blue one should be soldered onto one of the

holes near the fuse clip (Figure 15-9).

Next take a small piece of thick copper wire

and separate the insulation from the copper wire

(making sure that you keep the insulation intact as

we will be needing this later!). The wire should be

bent at one end and soldered first into the hole

adjacent to the motor clip, and then to the motor clip

Figure 15-10

Step 5—assembling the Solaroller.

Project 39: Build Your Own Solar Car itself to provide mechanical support (Figure 15-10).

Image courtesy Solarbotics.

140

Project 39: Build Your Own Solar Car

Figure 15-13

Step 8—assembling the Solaroller.

Image courtesy Solarbotics.

Figure 15-11

Step 6—assembling the Solaroller.

Image courtesy Solarbotics.

Figure 15-14

Step 9—assembling the Solaroller.

Image courtesy Solarbotics.

Next, take a short length of that insulation that

you saved and slide it onto the motor shaft. Now

take the wheel and slide it over the insulation

(Figure 15-11).

The next step is dead simple! Trim the axles at

the front of your Solaroller (Figure 15-12).

Now tin the pads on the back of the solarcell

(Figure 15-13).

Now solder the wires to the tinned pad, and add

Figure 15-12

Step 7—assembling the Solaroller.

a little dab of glue in an area away from the soldered

Image courtesy Solarbotics.

joints to act as a strain relief (Figure 15-14).

141

Now solder the connections to the printed circuit

board (Figure 15-15).

Hold the cell to the light, supporting your solar

vehicle and check that it works. Now that you have

proved that the circuitry works, fix the solar cell to

your vehicle chassis.

Figure 15-15

Step 10—assembling the Solaroller.

Image courtesy Solarbotics.

Project 40: Hold Your Own Solar Car Race

You will need

Tip

●

A stopwatch

or

Lap timer software is a free download from:

●

Lap timer 200 software and a PC

www.gregorybraun.com/LapTimer.html

●

A number of solar cars

OK, so the World Solar Challenge, and the North

American Solar Challenge might be a little out of

build a PC interface for sensors which will sense

your reach; however, holding your own tabletop

when your car crosses the line.

solar car race certainly isn’t.

You might like to consider how you can make

The free lap timer software presents a high-tech

your team vehicles look different. A little cus-

alternative to simply using a stop watch to time

tomization with paint and graphics goes a long

your cars. The software comes with schematics to

way!

Project 40: Hold Your Own Solar Car Race

142

Project 42: Supercharge Your Solaroller

Project 41: Souping Up Your Solar Vehicle

●

Think about how you could make a solar

reduce control or the model’s ability to travel in a

concentrator with tin foil or Mylar reflective

straight line!

surfaces channeling more energy to your solar cell.

●

You can tweak the value of the 2.2 k bias resistor.

●

Experiment with different tire types. You might find

This will change the efficiency of the solar engine.

that some different wheels from another model car

Higher values will make your solar engine more

offer better grip.

efficient, but will increase the time taken to

●

Try replacing the front wheels with some kind of

charge. Smaller values will speed the rate at

skid. Think about reducing the Solaroller’s friction;

which the motor is triggered, but at the expense

however, as you reduce friction, you might also

of efficiency.

Project 42: Supercharge Your Solaroller

Additionally, you can add a diode which allows

The next thing to do is take your diode, and

your Solaroller to charge more than would nor-

solder it as shown in Figure 15-17. Make sure that

mally be possible. You have the option of using a

you orient the stripe on the diode or flat on the

bog standard glass diode or an LED.

LED correctly.

The first thing you will need to do is cut through

the PCB trace in Figure 15-16.

Figure 15-16

Cutting through the PCB trace. Image

Figure 15-17

Adding the diode. Image courtesy

courtesy Solarbotics.

Solarbotics.

143

Figure 15-18

Honda fuel cell vehicle. Image courtesy Honda.

passing an electric current through the water.

Fuel cell vehicles

There are other ways of producing hydrogen, but

whatever the method, this hydrogen can then be

In Chapter 17, you will learn about hydrogen fuel

used as an energy carrier to provide power for a

cells. Hydrogen isn’t a fuel as such—you can’t

fuel cell vehicle, such as the Honda FCX in

“dig it out of the ground,” and although it is the

Figure 15-18.

most common element in the universe, we can’t

access it in a readily usable way.

However, we are surrounded by water which is

Solar aviation

H O, this means that it contains two parts of

2

hydrogen for every part of oxygen.

Figures 15-19 to 15-21 show examples of

As you will see in Chapter 17, it is relatively

solar-powered flight. Figure 15-22 shows a

easy to separate the hydrogen from the oxygen by

fuel cell.

Solar Aviation

144

Solar Aviation

Figure 15-19

Centurion solar plane. Image courtesy NASA.

Figure 15-20

Helios solar plane. Image courtesy NASA.

145

Figure 15-21

Helios 2 solar plane. Image courtesy NASA.

Figure 15-22

Helios fuel cell diagram. Image courtesy NASA.

Project 43: Build Your Own Solar Airship

This project is one of the most ridiculously simple

You will need

projects in this book, yet it is also one of the most

visual and almost counterintuitive.

●

Solar airship tube (8 m of thin plastic tube)

You might be under the misapprehension that to

●

2 × cable ties

get things into the air you need sophisticated jet

●

Tether line (50 m)

engines or rocket thrusters. Certainly if you have

Project 43: Build Your Own Solar Airship

146

Project 43: Build Your Own Solar Airship

Note

The kit for this project is well worth the spend, if

only for the enormous scale of the airship—it is a

massive 8 meters long. However, if you want to

experiment, you could get some good results with

cheap black plastic bin liners—why do I say

cheap? Well cheap bin liners tend to be made out

of thinner plastic and so are lighter for the

amount of air they enclose. As they are already

sealed at one end, you can get away with one

cable tie for one end, and some fine fishing line

for the tether.

read my other book 50 Model Rocket Projects for

the Evil Genius (intentional plug) you will know

all about rocket motors and what they can do—but

Figure 15-23

Solar airship.

hang about! There are also much simpler ways of

getting things to fly, and believe it or not, they

involve solar energy!

The procedure for flying a solar airship is

simplicity itself. Take the long plastic tube. Put a

Online resources

cable tie around one end. Then, holding the other

open, run until the tube is full of air. Try and fill it

Solar airship links

as much as you can and then bunch up the end and

Here are a number of places on the web where

tie it tight with another cable tie. Attach the tether

you can buy your own solar airship tube.

line to one of the cable ties.

www.eurocosm.com/Application/Products/

Now, place your solar airship in the sun and

Toys-that-fly/solar-airship-GB.asp

watch what happens.

www.amazon.co.uk/exec/obidos/ASIN/

Gracefully, slowly, you will see your solar air-

B000279OKI/202-9916112-9335805

ship begin to twitch a little, and then rise into the

www.find-me-a-gift.co.uk/gifts-for-men/

air. Hang on to that tether—else it might escape

unusual-gadgets/solar-airship.html

you (Figure 15-23)!

www.comparestoreprices.co.uk/novelty-gifts/

As the airship ascends into the sky, you might

unbranded-8m-solar-air-ship.asp

like to take a few moments to think about what is

This experiment has got to be seen to be

happening here.

believed! If you want to check out someone else

doing it first, you might like to take a look at this

Look at hot air balloons—they are lifted by burn-

video on the net.

ing gas, a hydrocarbon, but what actually happens

is that the gas is heating the volume of air inside

www.watchondemand.co.uk/solar-airship.htm

the balloon. As the air is heated, it becomes less

147

Figure 15-24

Could solar sails be used for space

Figure 15-25

A solar sail unfurled in flight. Image

travel? Image courtesy NASA.

courtesy NASA.

dense and therefore wants to float above denser

of which is where does the energy come from to

air—this provides a lifting force. Simple really!

propel a vehicle all that distance through space?

One possible answer could come in the form of

a solar sail (Figure 15-24).

What does the future

The sail shown in Figure 15-25 would be esti-

hold?

mated to be half a kilometer across! Although the

push provided by solar radiation is small, being

harnessed over such a large area it is strong

Space travel has long been a dream of futurists and

enough to provide propulsion.

science fiction lovers alike. However, traversing the

voids of space presents a number of problems—one

What Does the Future Hold?

148

Chapter 16

Solar Robotics?

I would like to thank Dave Hrynkiw at Solarbotics

natural gas, and other fossil fuels have powered the

Ltd for his help in preparing this chapter.

wheels of industry and automation. While automa-

Over the past century, we have seen a relentless

tion requires less human input, it does require

march toward a world of automation and ease.

energy.

Ever since the industrial revolution, increases

Thus we have enslaved ourselves to previously

in efficiency have been made by using automatic

plentiful fossil fuel energy, and created a world

devices and robots to take over the menial tasks

which would be much changed without it.

of man.

In the field of energy and robotics, we could then

As a result, we have given ourselves over to the

go on to say that if we want to push the boundaries

machine, and our modern world is dependent upon

of what we know, into the deep uncharted realms

the functioning of these devices for our continued

of space, exploring other planets (Figure 16-1)

development and growth.

(or closer to home, remote inaccessible areas like

This presents us with a little bit of a dilemma.

the sea), we need to provide energy for these dis-

The machines and automation of the industrial

tant ventures—this is hard with conventional

revolution were fueled by coal. More recently, oil,

means.

Figure 16-1

Spirit Mars rover. Image courtesy NASA.

149

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

The Spirit Rover which was sent to Mars, was

equipped with a 140 W array.

The circuit that the Photopopper Photovore uses

is called a “Miller Engine” circuit (Figure 16-2),

We see the increasing penetration of robots into

the solar cell charges a power capacitor, which

our households—Roomba and Scooba are

stores the power ready to be used in bursts by the

household names and represent readily available

motor. The circuit uses a 1381 voltage trigger to

domestic robots. However, at present, service

trip the motor circuit, once the solar cell has

robots need clumsy recharging stations. What if

charged the capacitor sufficiently. Once the

your domestic robots could roam freely around

capacitor has discharged beyond a certain point,

your house powered by nothing more than the sun

the 1381 cuts off, and stops the motor—allowing

shining through your window, and the ambient

the capacitor to charge. While you can use this

light in your rooms?

circuit as a basis for your own designs, a full kit

of parts for this robot is available from

Solarbotics (see the Supplier’s Index).

BEAM robotics

BEAM (Biology, Electronics, Aesthetics, and

Photopopper behaviors

Mechanics) robotics differ from traditional robotics

in one important respect—whereas conventional

Although simple, we see a number of emergent

robotics tends to employ a central processor and

behaviors as a result of the simple interconnections

some software to dictate the behavior of the robot,

of the above circuit.

BEAM robotics has a different approach. The

The first behavior that we see, is a light-seeking

robotic behavior is governed by simple circuits

behavior. This means that our Photopopper will try

which interact with each other in defined patterns.

to seek light and avoid shadow wherever possible.

This behavior was exhibited in Grey Walter’s turtle,

an early robot which proved that a limited number

Note

of connections could give rise to more complex

emerging behaviors.

The great news is that all of the above is available

We can see the way the robot makes its way

in a kit from Solarbotics.

toward a light source in Figure 16-3.

Check out www.solarbotics.com/ for more

When we try and relate our mechanical robot

details.

beastie to the world of the animal kingdom, we can

There is a coupon at the back of this book

see that light is the “food” for our robot—a natural

which will help you secure a discount on

animal instinct is to go where there is food in order

Solarbotics products.

to survive—it is clear that this robot exhibits this

behavior trait.

The Photopopper Photovore

Another behavior that our robot exhibits is

“obstacle avoidance” behavior, where the robot

The Photopopper Photovore is a nippy little robot

tries as far as possible to avoid obstacles by using

powered only by solar energy. While very simple

its “whisker” touch sensors (Figure 16-4). Again,

in nature, it demonstrates that solar-powered

we can relate this to the animal kingdom, where

devices can perform simple autonomous

whiskered animals such as hamsters and cats sense

functions—this sets a precedent for much larger,

obstructions with their sensitive whiskers and take

Solar Robotics more complex devices.

evasive action to avoid those obstacles.

150

Solar Robotics

Figure 16-2

Photopopper Photovore schematic. Image courtesy Solarbotics.

151

You might say this is a very nice novelty, but

but not where it sensed that there were borders full

where is the practical application? Sensing light

of flowers or garden ornaments. As you can see,

and touch is an analog for sensing any number of

these behaviors, which on the face of it are very

variables. Imagine a robotic Hoover that would

simple, can be combined to make an automated

vacuum the carpet of your room, but not when it

device that has more complex behaviors, and can

touched a wall or a piece of furniture, powered

relieve the tedium of simple human tasks, while

only by the sun and ambient light. Or imagine a

at the same time not consuming precious fossil-

robotic lawnmower which would mow the lawn,

fuel energy.

Figure 16-3

Photopopper light-seeking behavior. Image courtesy Solarbotics.

Solar Robotics Figure 16-4 Photopopper obstacle-avoiding behavior. Image courtesy Solarbotics.

152

Project 44: Assembling Your Photopopper Photovore

Project 44: Assembling Your Photopopper Photovore

Now, collect all of the components together for

We are now going to install the two diodes. Be

your Photopopper. They should look something

careful when handling these components, as they

like Figure 16-5.

are made of glass, and so are fairly fragile. You

Once you have gathered all of your components,

need to observe the stripe printed on the glass

you need to take your printed circuit board (PCB),

casing—diodes will only work correctly if they are

and the pair of 2N3906 transistors, and solder them

inserted the right way round, so make sure that you

to the board so that the curved side of the transistor

get this right.

matches the curved symbol on the circuit board.

If you have bought the Solarbotics PCB, you will

You can see that the transistors go either side of

see that the stripe on the board denotes which way

the area marked “Trim Pot.”

to solder this particular component (Figure 16-8).

This is illustrated in Figure 16-6.

Next take the pair of 1381 voltage triggers, and

Now we move on to Figure 16-7, where we will

solder these in at the top of the board. They need

solder the trimmer potentiometer in between the

to be installed in a similar manner to the transis-

two transistors that we have just added to the PCB.

tors, with the curve matching the legend on the

In this circuit, our trimmer potentiometer acts as a

PCB. Take note of the orientation of the compo-

“steering wheel” for our robot—we need to cali-

nents in the picture to ensure that the flat sides are

brate it so that our robot travels in a straight line,

correctly oriented (Figure 16-9).

which allows us to manually calibrate our robot.

There are now two capacitors which need to be

The leads will only allow the component to go in

soldered at the very top of the circuit board. These

one way, so it is hard to get wrong.

capacitors are not electrolytic capacitors, so it

Figure 16-5

All of the components for the Photopopper Photovore.

153

Figure 16-7

Adding the trimmer potentiometer.

Figure 16-6

The transistors—the first stage of

Image courtesy Solarbotics.

assembling your Photopopper Photovore. Image

courtesy Solarbotics .

Figure 16-8

Installation of the diodes. Image courtesy Solarbotics.

doesn’t matter which way round they are soldered

Now we are going to install the 4,700 µF power

into the two holes. If you are having trouble locating

capacitor (Figure 16-12). Unlike the two smaller

the capacitors, take a look at Figure 16-10.

capacitors that we installed earlier, this one is

Now take the two optical sensors, and solder

polarity sensitive as it is an electrolytic capacitor,

them so that the sensing element (which is the

so we need to make sure that we install it the

curved face) is facing outwards as shown in

correct way round. The capacitor will have a stripe

Figure 16-11. The optical sensors are photodiodes,

in light blue, with minus symbols running down

which allow a variable amount of power to flow to

next to one lead. The PCB also has a pad marked

the capacitor depending on how much light is

with a minus symbol—so these two need to go

Project 44: Assembling Your Photopopper Photovore hitting them.

together. You also need to make sure that the

154

Project 44: Assembling Your Photopopper Photovore

Figure 16-11

Installing the photodiodes. Image

courtesy Solarbotics.

Figure 16-9

Installing the 1381 voltage regulators.

Image courtesy Solarbotics.

Figure 16-12

Installing the power capacitor. Image

courtesy Solarbotics.

capacitor lies flat against the circuit board; so you

will need to bend the leads at 90°, once you have

ascertained which way round the capacitor is going.

The next step is to attach the motor mounts for

the tiny motors which will provide the movement

for our robot. This is shown in Figure 16-13. These

motor holders are in fact fuse clips. You need to

solder them to the two small tabs which stick out

of the side of the flexible circuit board. There

is a slight complication here, in that rather than

Figure 16-10

Inserting the two capacitors. Image

soldering the other side of the circuit board where

courtesy Solarbotics.

the pin protrudes, you need to solder on the same

155

Figure 16-15

Putting the motors in place.

Image courtesy Solarbotics.

Figure 16-13

Soldering the motor clips onto the PCB.

Image courtesy Solarbotics.

the little lip will prevent the motor from locating

properly.

Now, you will notice that the printed circuit

board is a little bent—this is how it is supposed to

be; however, in order to keep it rigidly bent, a

piece of supporting wire needs to be soldered to

support and maintain tension. You want to take the

stiff piece of wire, strip some insulation off one

end, and solder in the place where there is a hole

marked “wire” near the motor clip. Now, pull the

piece of wire to the other motor clip, strip the

insulation from that end, and solder it in place to

the other hole.

Figure 16-14

Both motor mounts ready. Image

Once the motor clips are in place (and you have

courtesy Solarbotics.

given them a while to cool down!) you need to

think about the small motors (Figure 16-15). If you

have bought the motors from Solarbotics, they will

side as the clip (Figure 16-14). This can be a little

come supplied with a red wire and a blue wire. It is

tricky.

important that the correct polarity is observed when

Some fuse clips come with a little lip molded

soldering the motors, as failure to do so will result

into the metal spring in order to try and retain the

in incorrect operation of your Photopopper.

fuse. If the fuse clip you buy is of this type, you

The PCB from Solarbotics clearly labels the

need to be able to solder the clip onto the board

attachment point on the circuit board M-Blue and

with this side facing the center line of the printed

M-Red. Take care when soldering the motor leads,

circuit board. If you don’t do this, then it will be

as they are delicate and the motor insulation is

Project 44: Assembling Your Photopopper Photovore next to impossible to seat the motor comfortably as easily damaged by the soldering iron.

156

Project 44: Assembling Your Photopopper Photovore

Figure 16-16

Connecting the solar cell.

Image courtesy Solarbotics.

Also, if you need to strip any insulation from the

wires, do so very carefully as it is very easy to break

Figure 16-17

Connecting the solar cell to the PCB.

the connection between the motor and wire—and a

Image courtesy Solarbotics.

lot harder to fix it back again!

Next comes connection of the robot’s

powerplant— the solar cell. First of all, take your

soldering iron and tin the pads of the solar cell.

Then solder a short length of wire to the pads. At

this point, in order to provide a little strain relief

for the wires and the carefully soldered joints, you

might want to take a little hot melt glue or epoxy,

and glue the wires to an area of the solar cell (for

example the area between the solder pads) where

there is no solder.

You will notice that one of the pads of the solar

cell is round, and the other is square. The round

pad is positive and the square pad is negative. So

solder the black to the square and the red to the

Figure 16-18

Attaching the solar cell.

round. This is shown in Figure 16-16.

Image courtesy Solarbotics.

Then, take the wires and, ensuring polarity,

solder them to the PCB (Figure 16-17).

The same convention as used on the solar cell

Now what you need to do is stick the solar

has been used with the pads on the PCB—the

cell to the PCB using a double-sided sticky pad

round one is a positive terminal and the square one

(Figure 16-18).

a negative.

Now take a short 10 mm length of heatshrink

This should be a real Frankenstein’s monster

tubing and slip it over the tiny shaft of one of the

moment, as your robot will now start to twitch

motors. Using a source of heat, such as a lighter or

with the first indications of light! The circuit is

match, shrink the tubing onto the shaft.

now complete, and as the capacitor charges the

Now comes the fiddly fine-tuning—there is a

motors will start to whirr!

small trimmer potentiometer (trim pot) that you

157

Figure 16-19

Assembling the spring/socket assembly. Image courtesy Solarbotics.

installed in the center. Well think of this as a bit of

Now we are going to assemble the touch sensors

a manual steering wheel for our Photopopper.

for our robot. Take the small Augat sockets, and a

What this trim pot essentially does is adjust the

7 mm length of heatshrink tubing, and shrink the

amount that our robot veers to the left or to the

tubing onto the socket.

right. So we can use it to compensate for any stray

Now trim the tubing with a sharp knife below

variables that could cause our robot to track off

the neck of the socket and slide off the excess.

center.

Taking the spring, stretch it a little, and push the

Augat connector into the center of the spring.

Take a small jeweller’s screwdriver to adjust the

Follow Figure 16-19 which illustrates the stages of

trim pot. Turn the screw at least 20 times to the

constructing the spring/socket assembly.

left—you should find that only the left motor acti-

vates. Now take the screwdriver and turn it the other

Once you have completed this stage, you will

way. You will find that the other motor activates.

want to think about soldering it to the circuit board.

Now turn the trimmer 10 turns to center it—both

You need to solder the pin to face forward as

motors should turn equal amounts at this point.

shown in Figure 16-20, and then the spring wire to

the adjacent pad.

If your robot persistently wanders to one side or

the other, then turn the screw in the direction of the

Now you can curl the wires in different configu-

Project 44: Assembling Your Photopopper Photovore engine which needs more power.

rations. Experiment with making the wires different

158

Project 44: Assembling Your Photopopper Photovore

Figure 16-20

Attaching the touch sensor to the PCB. Image courtesy Solarbotics.

shapes and seeing how it affects their ability to

sense. Moving the wires to different positions will

allow the robot to sense different zones in front of

it. Experiment to see which arrangement makes the

robot navigate most effectively.

Building your own

solar robots

Armed with these simple principles you can go on

to create your own solar robots.

The key to the design is the solar motor schematic

and interconnection of lots of small simple

“neuron” circuits.

Figure 16-21

Solar motors are high-efficiency.

Taking it further

Try and buy high-efficiency motors (Figure 16-21),

If you want to find out more about BEAM robotics,

as they will produce the best performance from

I can highly recommend the publication Junkbots,

relatively modest solar cells.

Bugbots & Bots on Wheels by Dave Hrynkiw and

You might find old scrap electrical devices to be

Mark Tilden, published by McGraw-Hill.

a great source of small motors! Look around for

159

battery-powered, or low-voltage home devices

which contain motors sufficiently small to be

driven by solar power. Devices containing tape

decks yield a variety of small motors (Figure 16-22),

so look out for old Walkmans, Dictaphones, and

answering machines especially.

Figure 16-22

Electrical devices are a great

source of motors!

Building Your Own Solar Robots

160

Chapter 17

Solar Hydrogen Partnership

“Fuel cell technology is so appealing that it will

The hydrogen economy entails a transition from

have an enormous impact across all energy

carbon-rich fuels (such as the fossil fuels we use

markets.” K. Atakan Ozbek, Allied Business

today) to hydrogen, and carriers of hydrogen such

Intelligence Senior Analyst.

as methanol.

One of the problems that we have seen with

Electricity is generated in the usual way from

renewable energy is “intermittency.” Unlike coal,

renewables—a nice mixed portfolio of wind, solar,

gas, and oil, where the amount of energy we

wave, and tidal energy, producing power as and

produce is determined by the amount of fossil fuel

when the weather permits.

we input into the process, things with renewable

energy are slightly different—we must live with

the energy that the weather gives us.

So what is so great about

This presents us with a choice. We can tailor

the hydrogen economy?

our energy demands to when the energy is

available. In some situations this is practical;

The hydrogen economy could have a number of

however, in most situations, there is an urgency

benefits, both economic and environmental. For a

to our demand for energy.

start, when you burn hydrogen, you don’t produce

We can meet this demand in a number of ways.

carbon dioxide, which is produced with carbon-

We can connect together renewable energy sources

based fuels and is a major contributor to the green-

that are distributed over a wide area, “a National

house effect. In addition to this, you don’t get any of

Grid” as it were. While this is helpful, it is not a

the other nasties such as oxides of sulfur and nitro-

complete solution—we hope that there will be sun

gen that you get with burning conventional fuels.

in one area when there is not in another, but we

Then there are the economic benefits. At the

cannot guarantee it! Furthermore, by transmitting

moment, the United States, and many other coun-

electricity over long distances, there is a certain

tries, cannot produce enough oil to meet their

amount of “loss” inherent in the system. The elec-

demand for energy. This places those countries in a

tricity gets “lost” as a result of resistance, decreas-

situation where they are dependent upon the

ing the total amount of useful energy available.

Middle East and other oil-rich nations to provide

So, what do we do? Storing the energy would

the energy to power their economies. This is not a

seem like an obvious candidate. But the problem is

good position for a country to be in.

that present battery technology is fairly heavy,

It has bad consequences, as it means that in

inefficient, and expensive.

order to get oil, a desperate country might resort to

In steps . . . the Fuel Cell.

any means within its power to secure that vital

The fuel cell—and the hydrogen economy it

supply of fossil fuel. This could even include war.

entails—is put forward by many as the answer to

By contrast, there is nothing about hydrogen that

our impending energy crisis.

says it must be produced in a particular location.

161

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

As long as the two fundamental factors are pre-

efficient power source, communities will get zero

sent—electricity and water—it can be produced

emissions, and automakers will get another major

anywhere.

business opportunity—a growth opportunity.”

One of the great advantages of the “hydrogen

William C. Ford, Jr, Ford Chairman, International

economy” is that it works very well with decentral-

Auto Show, January 2000.

ization. To understand what decentralization and

“Fuel cell vehicles will probably overtake

decentralized power generation means, think “don’t

gasoline-powered cars in the next 20 to 30 years.”

put all your eggs in one basket.” To explain this a

Takeo Fukui, Managing Director, Research and

little further, at present, power is generated in bulk

Development, Honda Motor Co., Bloomberg News,

in large centrally managed power stations. This has

June 5, 1999.

been so because up until now (we have been kid-

ding ourselves) there has been an abundance of

energy-dense fuels that we can use to meet our

So is there only one type

power needs.

of fuel cell?

Now envisage a world where rather than pol-

luted atmospheres and mountains of toxic nuclear

No, there are lots! Each type of fuel cell is suited

waste, we instead have “distributed” energy pro-

to different applications. Broadly speaking, fuel

duction. This means solar cells on roofs, and wind

cells can be divided into two main kinds—high

turbines here and there, integrating with the fabric

temperature and low temperature.

of our towns and cities. All of these devices pro-

duce a small amount of power—but the key is they

Figure 17-1 shows the main areas of focus in

produce it where it is needed.

fuel cell technology, where research capital is

being invested.

We are going to be experimenting with a type of

low-temperature fuel cell—the PEM fuel cell

How will fuel cells

which stands for Polymer Electrolyte Membrane,

or Proton Exchange Membrane depending on who

penetrate our lives

you listen to!

in the future?

You can expect to see fuel cells in all the places

What is a fuel cell made

you see rechargeable batteries at the moment—

and many more. Fuel cells offer the prospect of

up of?

laptop computers that can be used many times

longer than conventional batteries allow, mobile

If we were to take a fuel cell to bits, we would see

phones with much longer periods of talk time

that it is mechanically very simple. Take a peek at

than is possible with present battery technology,

Figure 17-2.

and vehicles with clean emissions of nothing but

We can see that the fuel cell has two end plates.

water.

These are used as a casing for the fuel cell. They

“I believe fuel cell vehicles will finally end the

help contain the internal elements; furthermore,

hundred-year reign of the internal combustion

they provide an interface to the connection for

engine as the dominant source of power for per-

hydrogen and oxygen gas.

sonal transportation. It’s going to be a winning sit-

Next up are the electrodes. These are the pieces

Solar Hydrogen Partnership uation all the way around—consumers will get an that allow us to “tap off” electricity. They are

162

Solar Hydrogen Partnership

Figure 17-1

Fuel cell technology focus.

Figure 17-2

Fuel cell construction.

generally made from stainless steel, as it does not

that interfaces with the Nafion membrane (more on

react with the chemicals present. The stainless

that later)—contains a quantity of platinum which

steel is perforated to allow the gas to penetrate.

acts as a catalyst for the reaction that will take

The next assembly of carbon cloth/paper and

place next.

Nafion membrane is termed an MEA, or membrane

Now the Nafion membrane—but first a little

electrode assembly. This is the bit that makes the

explanation!

reaction take place that produces the energy.

For those of you who were wondering, Nafion is

Next we have a carbon cloth or paper. The gas

a sulfonated tetrafluoroethylene copolymer. Are

can permeate this quite easily, one side—the side

you any the wiser? Well Nafion is a special kind of

163

plastic developed by DuPont in the 1960s. It’s very

so the electrons make their way through the circuit.

special properties are essential to the operation

As they do this they perform some useful work

of the PEM fuel cell. Essentially, what happens is

which we can harness.

that electrons cannot pass through the Nafion mem-

On the other side of the Nafion membrane is a

brane but protons can. The platinum on the carbon

mirror image assembly, with another set of carbon

Energy cloth facilitates the separation of the electrons from cloth, stainless steel electrode, and end plate.

the protons in the hydrogen atom. The protons are

allowed to pass through the membrane; however,

At the other side, the electrons are reunited with

the electrons can’t get through. Instead, they take

the protons that have passed through the mem-

the next easiest route.

brane, and the all-essential oxygen. The protons,

electrons, and oxygen combine to form H O—

The carbon cloth acts as a conductor. It allows

2

better known as water.

the electrons to find a path to the stainless steel

mesh. The mesh forms the electrode, which is

We will look at this process in more detail

connected to the circuit that the fuel cell powers.

later, but first let’s get on with generating some

The circuit presents the route of least resistance,

hydrogen!

Project 45: Generating Hydrogen Using Solar Energy

In this project, we are going to look at the potential

You will need

for a solar-hydrogen economy.

We are going to start with a simple experiment

●

PEM reversible fuel cell (Fuel Cell Store part no.

632000)

to generate hydrogen using a solar cell to provide

the electricity to electrolyze water.

●

Photovoltaic solar cell (Fuel Cell Store part no.

621500)

●

Gas storage tank (2 ×) (Fuel Cell Store part no. 560207)

Familiarizing ourselves

●

Rubber tubing

with the stuff!

●

Distilled water (not just purified!)

If you have bought the items above, the chances

Tools

are that you have got a lot of cool stuff, but are

none too sure what to do with it. Don’t panic!

●

Crocodile clip leads

We are going to look at what the stuff does, and

●

Syringe

how it all goes together in this section.

First is our fuel cell, shown in Figures 17-3

Fuel cell tech spec

to 17-5.

First of all, you should note two terminals on the

PEM reversible fuel cell

top—one red, one black. It should be apparent that

2 × 2 × 1/2 in. (5 × 5 × 12.5 cm)

these are the supply terminals for the fuel cell.

2.4 oz. (68 grams)

Then, if we look on either side of the fuel cell, we

see that there are intake pipes for gas. There

0.95 volts open circuit

should be two, these are diagonally offset in the

350 MA

Project 45: Generating Hydrogen Using Solar

fuel cell specified above.

164

Project 45: Generating Hydrogen Using Solar

Figure 17-5

PEM fuel cell with rubber hoses.

Figure 17-3

PEM fuel cell with caps.

Figure 17-4

PEM fuel cell without caps.

Figure 17-6

40 ml “gas tank” filled with water.

You will see that one side of the fuel cell has a

label “H2,” this is the hydrogen side; the other side

tube are shown attached to the fuel cell in Figure

has the label “O2,” this is where the oxygen goes.

17-5.

The fuel cell comes supplied with some little

Next we have the “gas tanks” shown in Figures

Energy

caps as shown in Figure 17-3. These can be used

17-6 and 17-7.

to prevent water from escaping. These caps can be

We can see how in the first instance we fill the

removed if desired, and two little plastic tubes

gas tanks with water—this is illustrated in Figure

are exposed for connection to the gas tanks

17-6. Then, as shown in Figure 17-7, as our fuel

(more about this later). Small lengths of rubber

cells produce gas, the gas displaces the water

165

which goes into the top half of the cylinder.

The weight of this body of water acting on the

Preparing the fuel

gas provides a little pressure on the gas—enough

cell for electrolysis

to speed its return to the fuel cell.

Before we can electrolyze water, we need to prime

We also connect the other pipe to the tank to

Energy

the fuel cell with water so that it has something to

enable the excess water to return.

electrolyze. For this, we will be using distilled

The fuel cell is connected mechanically as in

water. It is important that the water that you use is

Figure 17-8. Note that the oxygen feed is

“distilled water,” which should be readily available

connected in the same manner as the hydrogen.

from the drug store, not just “purified” water.

Water from the tap, even water from the chiller,

contains trace elements that have the potential to

wreak havoc with the delicate little MEA inside

our PEM fuel cell.

First of all, you need to prime the fuel cell with

water. A syringe and some small bore rubber

tubing helps you accomplish this easily. Fill the

fuel cell through one of the holes, allowing air to

escape from the other. Once you have done this,

put the caps back on the gas intake tubes of the

fuel cell to prevent any ingress of air.

Fill the gas cylinders with water as well, and then

connect it all up as shown in Figure 17-8. If there

are any little gas bubbles trapped in the pipes, these

must be bled out of the system first of all.

Now we come to connecting our solar cell.

Wiring up the solar cell

and fuel cell

Figure 17-7

40 ml “gas tank” filled with gas.

Once the “mechanical engineering” is complete,

we need to work on the “electrical engineering.”

Luckily, connection is very simple indeed. Take a

peek at Figure 17-9 which shows how it is done.

Project 45: Generating Hydrogen Using Solar Figure 17-8 How to connect the pipes to the fuel cell.

Figure 17-9

Connecting the two cells.

166

Project 45: Generating Hydrogen Using Solar

Logic should tell you that the red terminal on

In fact, at the moment, most hydrogen is pro-

the fuel cell is positive and the black terminal is

duced using a process known as steam reforming.

negative. Use your crocodile leads to connect things

This takes fossil fuels and combines them with

up and put your solar cell somewhere where it will

steam, which disassociates the hydrogen from the

receive good light.

carbon, However, do not be fooled! This process

still leaves a whole lot of carbon dioxide to be

Observation

gotten rid of.

At the moment, there is talk of a technology

Don’t hold your breath, the process is going to

called “sequestration.” Sequestration involves sepa-

take a little bit of time! Over time you should

rating the carbon dioxide emissions from industry

observe a number of things happening. Gas will

or an item of plant. They are then piped to a facil-

begin to form, and is collected in the two

ity where they can be forced underground into

cylinders, displacing the water as it does so. You

natural geological features which supposedly

will notice that twice as much hydrogen is

will keep the carbon locked up under the earth’s

produced as is oxygen.

surface. Put simply, this technique involves hiding

the problem by burying it underground. It is a

What is happening here?

good technology in so far as it allows the oil com-

panies to maintain the status quo by continually

The chemical symbol for water is H O. Those

producing oil. However, the carbon dioxide is still

2

with even a smattering of knowledge of chemistry

present—albeit “sequestered” underground. There

will know that this means a water molecule is

is also another incentive for companies to adopt

comprised of two hydrogen atoms and one

sequestration—it increases their oil production!

oxygen atom.

By forcing gas underground, more oil comes to

When we pass an electrical current through the

the surface. Economically it makes good sense,

water, using the reversible fuel cell as our

environmentally the case is yet to be proven. No

electrolyzer, we are splitting the water into its

one has yet tried sequestration on the scale proposed

constituent parts—hydrogen and oxygen.

before—it is unknown whether this gas will find

ways of escaping back to the atmosphere.

Because of the membrane inside the fuel cell,

the hydrogen and oxygen are kept separated. The

One method proposed for making hydrogen

hydrogen and oxygen can then be piped off, and

using solar energy, is to use bacteria to produce it.

stored in tanks, where the hydrogen and oxygen

Using a process of photosynthesis, certain algae

can be saved for later use.

and bacteria have been shown to produce hydrogen

gas. This hydrogen can be harnessed and used to

power the hydrogen economy.

Other methods of

generating hydrogen

Online resources

Energy

There are also a number of other proposed

methods for generating hydrogen from solar

This is a good website to check out that talks

energy, which, although we are not going to

about the bioproduction of hydrogen.

examine them in detail here, are certainly of

www.energycooperation.org/bioproductionH2.htm

merit.

167

Project 46: Using Stored Hydrogen to Create Electricity

You will need

●

PEM reversible fuel cell (Fuel Cell Store

part no. 632000)

●

Photovoltaic solar cell (Fuel Cell Store

part no. 621500)

●

Gas storage tank (2×) (Fuel Cell Store

part no. 560207)

●

Rubber tubing

●

Distilled water (not just purified!)

●

Small load (only a volt or two)/variable resistor

Figure 17-10

Schematic representation of a PEM

fuel cell.

Tools

●

Ammeter

●

Voltmeter

We have seen in the previous experiment, how

we can use electricity, more specifically “solar

power,” to generate hydrogen. We also saw that

this hydrogen can be stored for later use. Now, in

this part of the experiment, we are going to look at

turning this hydrogen into electricity, and what is

actually happening.

In the hydrogen economy, hydrogen which is

generated from surplus, cheap renewable energy,

Figure 17-11

Hydrogen enters the fuel cell.

can be distributed through a network of pipes and

used to provide power in the home via a small

Stored Hydrogen to Create Electricity residential generator (which produces useful heat A reaction occurs as a result of the platinum

as a byproduct). Additionally, this hydrogen can

catalyst. The electrons cannot go anywhere, as they

be used to run motor cars or public transportation

cannot penetrate the membrane formed by the

systems if stored in tanks on the vehicle.

MEA, so they go round a circuit because this is the

We are now going to see how a fuel cell converts

easiest path for them to take. Meanwhile, the

this hydrogen back into electrical power.

protons escape across the membrane. This is

Figure 17-10 gives a schematic representation of

illustrated in Figure 17-12.

our fuel cell, showing the major parts.

As the electrons travel around the circuit,

If we look at Figure 17-11 we can see hydrogen

they do some useful work. For example, in

Project 46: entering the fuel cell—ready to do its thing!

Figure 17-13 they are lighting a bulb.

168

Project 46:

Stored Hydrogen to Create Electricity

Figure 17-12

The protons and electrons separate.

Figure 17-13

The electrons “do some work.”

At the other side of the membrane, the electrons

(which have passed around the circuit), the protons

(which have crossed through the membrane), and

oxygen (from either the air or oxygen tanks), are

brought together, where they react. You can see

this in Figure 17-14.

The product of this reaction is water, H O

2

(Figure 17-15).

This process is happening continuously rather

than in discrete stages. All the time there is a never

Figure 17-14

The electrons, protons, and oxygen

ending ceaseless flow of electrons, protons,

are reunited.

hydrogen, and oxygen.

and ammeter will confirm that you are producing

Connecting up your fuel cell

power.

We now need to connect up our fuel cell as shown

Well done—you have made another great step

in Figure 17-16. The mechanical setup remains the

toward the world understanding the hydrogen

same as for the last project. However, rather than

economy and applying it in practice!

being connected to a solar cell, we are connecting

our fuel cell to a load, so that energy can be

extracted.

Note

We are monitoring this load with a voltmeter and

ammeter.

For a demonstration in an educational setting, the

Eco H /O system available from Fuel Cell Store

Instantly, you should see the amount of hydro-

2

2

(see Supplier’s Index) part no. 534407 offers a

gen and oxygen in the tanks decrease little bit by

great way to demonstrate the principles in this

little bit and bubbles flow through the pipes. Your

chapter, in a nice, desk-mounted study of solar

load, if it is a small bulb, motor, or just a resistor,

hydrogen electricity.

should show some sign of activity. The voltmeter

169

Figure 17-16

Circuit diagram.

The hydrogen economy isn’t something that is

going to happen overnight. Furthermore, it won’t

Figure 17-15

Water is produced.

be a single event where all of a sudden we switch

from one to the other. Instead, hydrogen technolo-

gies will gradually begin to permeate our lives.

Conclusion

This will probably start first of all with vehicles

and portable electronic devices, as these devices

I like to think of fuel cells as a bit like a

will benefit from lightweight, high-density energy

sandwich. If you can, imagine a cheese

storage that hydrogen affords. We can expect to

sandwich, with the two pieces of bread as

see hydrogen in more and more places. However,

the electrodes. Those pieces of bread are buttered.

there are technological hurdles that must be

It is this butter that effects the interaction between

overcome first of all.

the cheese and the bread—the butter can be

likened to the gas diffusion media.

Online resources

This website gives a particularly good animation

that clearly illustrates what is happening inside a

PEM fuel cell.

www.humboldt.edu/~serc/animation.html

Stored Hydrogen to Create Electricity

Project 46:

170

Chapter 18

Photosynthesis—Fuel from the Sun

We can harness solar energy in a lot of different

Some plants can be turned into oils. Remember,

direct ways, as we have seen already in this book.

each time you eat some French fries, they were

We can use the sun to meet our requirements for

cooked in oil which came from vegetable matter,

heat and electricity. Sometimes, as we saw in

often sunflower. This oil can be burned directly in

Chapter 17, we need energy sources that are

engines.

portable and lightweight—for powering cars, for

It is also possible to turn vegetable oils into a

example, and for transporting energy to sites where

product called “biodiesel.” Biodiesel can be used in

it is not appropriate to use solar energy directly.

most ordinary diesel engines as if it were any other

One way in which we can harness solar energy,

diesel fuel. The difference between the vegetable

is to produce plants that we can turn into fuels.

oil, which is a triglyceride, and the biodiesel, is that

Remember, plants use the sun’s energy to grow.

the biodiesel contains shorter hydrocarbon chains.

A plant takes in carbon dioxide from the

This means, that among other properties, the oil is

atmosphere, water, and nutrients from the soil, and

less viscous, which means that it flows more freely.

turns it into biological matter. The trees and

Another way that we can produce biofuels is to

flowers would not exist without the sun’s energy.

produce sugar crops, which can be fermented and

We see in Figure 18-1 the cycle that takes place.

distilled to produce ethanol. This ethanol can be

Figure 18-1

Biofuel—fuel from the sun.

171

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

used in gasoline/petrol engines with relatively little

important to note, that at other stages there are

modification.

inputs of energy. These might not always come

from renewable energy sources, and so it is

Countries like Brazil often use a blend of ethanol

important to be critical and consider how much

derived from plant matter, and gasoline/petrol from

“oil” might be in your biofuel.

conventional sources. This is sold as “Gasohol” in

many places. By blending the gasoline/petrol with

Some farming techniques rely on intensive use

ethanol, they are reducing their country’s depen-

of fertilizers and other agricultural chemicals—all

dence on imported oil. The U.S.A. and many coun-

tries of the “developed world” can learn a lot from

these developing countries, as the developed world

is now largely dependent on imported fuels from

the Middle East. The oil that is available on “home

turf” is now largely located in areas of outstanding

natural beauty, places that are very sensitive to

environmental change. U.S. oil companies are now

having to cut pipelines through swathes of Alaska,

causing enormous environmental damage. Surely

there are other solutions—solutions that can benefit

U.S. farmers?

If we look at how ethanol (Figure 18-2) is

produced, in Figure 18-3 we can see that the

Figure 18-2

A molecule of ethanol—a biofuel

process is driven by solar energy. However, it is

from the sun.

Photosynthesis—Fuel from the Sun Figure 18-3 Ethanol production.

172

Photosynthesis—Fuel from the Sun

of these require a vast input of energy to manufac-

ture. However, there are other farming techniques,

The four hydrogen rule

such as organic farming, which rely on natural,

low embodied energy techniques. The techniques

have been honed and refined over hundreds of

Let’s not get too hung up about chemistry here,

but at the same time, let’s try and understand how

years, and passed down through the ages (remem-

hydrocarbons work. By now, if you have been

ber industrialized farming is only a relatively

paying attention, you should realize that atoms of

recent phenomenon).

carbon and hydrogen combine to form molecules,

According to C.J. Cleveland of Boston University,

which we call hydrocarbons. This much was

annual photosynthesis by vegetation in the U.S.A.,

explained in the “Hydrocarbons” box. However,

is 4.7 × 1016 Btu, equivalent to nearly 60% of the

let’s try and understand the rules for the

nation’s annual fossil-fuel use. This suggests that

combination of hydrogen and carbon atoms.

the amount of plant matter growing is of a similar

A carbon atom has four “sites” where other

order of magnitude to the amount of energy that

atoms can potentially bond. In the simplest

we consume. It would not be feasible to meet all of

hydrocarbon, methane, all four of these sites are

our energy needs from biofuels, but it certainly

bonded to hydrogen atoms. We might also know

suggests that they could be used in a wider range

this chemical by the name “natural gas.” However,

of applications.

in addition to hydrogen atoms, carbon atoms can

also bond to these sites.

We can make chains of carbon atoms by

removing one hydrogen bond from each of two

methane molecules, and joining the carbons

Hydrocarbons

together by this “missing” bond.

We can make these chains longer and longer,

Hydrocarbons are chains of hydrogen atoms and

until eventually we start getting to the point

carbon atoms.

where we have eight carbons in a row. When we

have eight carbons joined by single bonds, we call

this “octane” and for this level of chemistry, we

can understand that “octane” is similar to petrol

Coal comes from periods in the world’s history

or gasoline. If we start adding carbons, we get to

when there were lots of trees and plants growing,

the point where we have between 10 and 15 in a

which died, and then were compressed by rocks

row. The diesel we use in our cars is a mixture of

and earth. The carboniferous matter in the coal

10–15 carbon long hydrocarbon chains.

(which means “containing carbon”), is actually

dead plants. Thus, we can see that coal was also

produced from solar energy.

The crucial difference to recognize between

Our ecosystem is a bit like a bucket with a hole

coal, fossil fuels, and the fuel that we call biomass,

in it under a tap. The tap is like the carbon dioxide

is that the biomass fuel has recently taken the

we are putting into the atmosphere, and the hole in

carbon dioxide, which is produced when it burns,

the bucket is like the mechanisms which remove

out of the atmosphere. By contrast, fossil fuels,

carbon dioxide from the air—the plants and

when burnt, are releasing the carbon dioxide which

vegetation which absorb CO and release oxygen.

2

was stored under the ground for many millions of

If we pour water into the bucket at the same rate

years. That is why, when we burn fossil fuels, we

that it flows out, then the level in the bucket stays

really are creating a massive problem.

constant.

173

If we are burning mainly biofuels, and replanting

Here we can see that water and carbon dioxide

the things that we burn, then we are only putting

combine to produce glucose and oxygen. The

carbon dioxide into the atmosphere which was

glucose is the “food” for the plant that enables it

removed recently. This is like pouring water in at

to grow.

the rate it flows out.

However, if we start turning the tap so that the

water gushes out, then the level in the bucket

A snapshot history

begins to rise.

of biofuel

At present, that is what we are doing—we are

turning up the tap on the carbon dioxide in our

Since the earliest days, when an intrepid caveman

atmosphere. We are letting it gush out of the tap

rubbed some sticks together and discovered he

rapidly, with the effect that it is now beginning to

could warm himself, and finally cook that hot meal

get to the point where we have more water in the

he had been dying for, we have been burning

bucket than it can hold safely!

biofuels. Wood has been a staple fuel for heating

This is because we are putting carbon into the

and cooking.

atmosphere which was safely tucked away millions

With the advent of the steam age (the invention

of years ago.

of the “external combustion engine”), it became

If you look at Figure 18-4, you can see that the

possible to turn heat into kinetic energy—motion.

plant is taking in water and carbon dioxide and

This paved the way for the industrial revolution,

producing oxygen. However, those with some know-

and brought us mechanized transport in the form

ledge of chemistry must realize that any equation

of early steam vehicles.

must be balanced. Take a peek at Equation 1.

Much of the industrial revolution was powered

by coal, as it was easy to extract and had a high

energy density. However, there are also numerous

examples of steam engines being powered by

Equation 1

The photosynthesis equation.

wood fuel.

This is all very nice . . . but things really start to

get interesting with the invention of the internal

combustion engine. This invention can be attrib-

uted to one Nikolaus August Otto (June 14, 1832–

January 28, 1891) whose picture you can see in

Figure 18-5. His idea was pretty revolutionary, and

really threw the cat amongst the pigeons. Rather

than burning the fuel “outside” of the cylinder, the

new idea was to burn the fuel “inside” the cylinder.

In May 1867, there was a new revolution, the inter-

nal combustion engine was born.

You might think that this is bad news for bio-

fuels, as it could be tricky squeezing large logs

inside a small cylinder. Quite the contrary in fact,

Otto’s original plan was to use ethanol, which

we have read about in this chapter. Ethanol is a

Photosynthesis—Fuel from the Sun Figure 18-4 Photosynthesis.

biofuel.

174

Photosynthesis—Fuel from the Sun

Otto’s company is still ticking over nicely and

consequences. There is a resurgence of interest in

now exists under the name Deutz AG.

biofuel technology—expect to hear much more

In a four-stroke, Otto cycle, internal combustion

about biofuels in the years to come.

engine, a spark ignites the mixture of fuel and air.

These are the type of engines you find in petrol or

gasoline cars.

Bad biofuels?

However, there is more to the story than that!

Biofuels got another boost when one Henry Ford

Well, all Evil Geniuses should be trying to form a

designed his mass-production “Model T” car to

balanced view of the arguments in the world they

run on ethanol! Unfortunately now, our story takes

are trying to conquer. Let’s take a look at the flip

a bit of a sinister turn.

side of biofuels and assess why, maybe, they aren’t

During the Second World War, with supplies of oil

going to save the world.

scarce, countries began to look at using biofuels to

Biofuels have an important role to play while we

meet the war-effort’s insatiable demand for energy.

look for medium-term solutions to our energy

Unfortunately, after this time biofuels take a bit

problems. In the longer term, technologies such as

of a turn for the worse. Oil became cheap and

the hydrogen economy and hydrogen fuel cells, could

biofuels disappeared into obscurity . . . until now.

potentially meet our energy needs. However, in the

short term, we need to look for transitional solutions

The western world is now finding it harder than

that will allow us to shift from our “dirty” technologies,

ever to find fossil fuels at acceptable prices—both

to more environmentally responsible technologies.

financial and environmental. As a result of the

Biofuels have a part to play in this transition.

world’s insatiable lust for oil, areas of outstanding

natural beauty such as Alaska are being plundered

However, if we look at trying to meet all of our

for their oil, with dire environmental

energy needs from biofuels, it becomes apparent

that “growing energy” may not be desirable on a

large scale. There is limited bio-productive land

(by which we mean land with the ability to

produce crops) in the world. We need some of this

land to live on, we need some of this land to

produce food to eat, and we need some of this land

for animals to graze. If you do the math, and look

at a future energy scenario where our needs are met

by biofuels, you find that it just doesn’t add up.

With rising populations, and hence rising demand

for food, and furthermore, rising expectations

from developing countries, it is apparent that at the

moment there isn’t enough land to meet our needs

wholly.

This doesn’t matter in the short-term, as there is

plenty of land that is yet to be put to good use, and

plenty of “biologically derived” waste products of

industry, that have the potential to provide us with

energy if we see them as a product rather than

Figure 18-5

Nikolaus August Otto.

something to be disposed of.

175

Furthermore, we need to look at products that are

crops using a small, more manageable plant: salad

currently treated as waste that could be used to

cress/mustard. To give you an idea of what you

provide energy. There are fast-food outlets on every

should be looking for at the garden center, here are

block that produce French fries by the million. In

the seeds that I used, pictured in Figure 18-6.

doing so, they consume copious amounts of vegetable

oil, which eventually ends up as spent oil to be

disposed of. Did you know that you can run a diesel

Note

engine on waste vegetable oil with minimal effort?

In order to conduct accurate experiments, we need

to control all of the variables as closely as we can, in

Watch the book sellers shelves, my forthcoming

order to make sure that our experiments are accurate

book Convert Your Vehicle to Biodiesel in a

and repeatable. Although it might seem a bit

Weekend will contain details of how you can

pedantic, try and ensure as far as possible that you

convert a diesel vehicle to run on vegetable oils.

give the plants the amount of water, cotton wool,

However, while running your vehicle on a waste

light, etc. as stated in the text. To ensure a fair test,

product might be saving the world in your own little

try and make sure that all things remain the same.

way, cutting down rainforests to plant fuel crops is

For example, if you put several tests on a windowsill,

ensure that they all receive equal light, and one is

not. Shamefully, this is what is happening in some

not in shadow and one in light.

parts of the world, which sort of defeats the object

of biodiesel being a more sustainable fuel.

Vast areas of rainforest are being devastated to

plant palm oil crops that produce quick oil—and

money—for the growers. However, for every acre of

rainforest we lose, we also lose a massive amount of

biodiversity—and a little bit of the earth’s lungs.

Moreover, planting large amounts of the same

thing, isn’t such good news for biodiversity. We need

a healthy mix of different flora and fauna—having

large overwhelming amounts of the same thing isn’t

particularly good for the ecology of the world.

Photosynthesis

experiments

In the following experiments, we will be analyzing

the solar-driven processes that happen in plants, to

produce usable products which we can burn as

biofuels. The process which we have explored

already, is called “photosynthesis.”

Sugarcane, rapeseed, and other crops which are

generally used to produce biofuel are a bit big,

hard to manage, and unpredictable. For this reason,

Photosynthesis—Fuel from the Sun we will be modeling the production of biofuel Figure 18-6

Cress seeds suitable for our experimentation.

176

Project 48: Proving Biofuel Requires Water

Project 47: Proving Biofuel Requires Solar Energy

out 20 cress seeds from the packet, and water them

You will need

evenly with 5 ml (5 cm3) of water. We want to

make our two cells as identical as possible; be as

●

40 salad cress seeds

accurate as you can, as in order for the test to be

●

Cotton wool (cotton batting)

fair, it must be repeatable.

Tools

One of these bowls should be placed on a bright

sunny windowsill. The other should be placed on

●

Two small bowls

the same windowsill but covered with a dark box,

to prevent any sunlight from reaching the seeds.

●

5 ml measuring syringe

In this experiment, we are going to test the hypo-

Observe the seeds over several days to see what

thesis that “biofuel requires solar energy in order

happens. Compare the two samples, but remember

to be produced.” In order to do this, we are going

to cover the “dark” seeds soon after taking a peek.

to set up two small test cells, which we will use

Your results should confirm the hypothesis that

to compare the growth of two samples of our

solar energy is required for seeds to grow.

“biofuel,” cress.

Of course, we can mimic the properties of sunlight

Take two small bowls. Fill the bottom of one

using artificial sources of light, but this would seem

with a layer of 2 cm of cotton wool. Carefully pick

self-defeating as it requires a lot of energy.

Project 48: Proving Biofuel Requires Water

This experiment is very similar to the previous one,

You will need

in that we will be comparing two different containers

of “biofuel crop.” The difference with this experi-

●

40 salad cress seeds

ment is that both will be exposed to bright sunlight.

●

Cotton wool

However, one will receive 5 ml (5 cm3) of water,

while the other will be on dry cotton wool.

Tools

The results of this experiment should seem

intuitive—if you don’t water plants, they die;

●

Two small bowls

however, the experiment is worth carrying out

●

5 ml measuring syringe

nonetheless.

177

Project 49: Looking at the Light-Absorption

Properties of Chlorophyll

You will need

●

Four identical boxes

●

80 salad cress seeds

●

Cotton wool

●

Colored filter gelatin red, green, and blue

Tools

●

Four small identical bowls

●

5 ml measuring syringe

Figure 18-7

Chlorophyll’s response to light.

You will need to attach a colored gelatin filter

Note

to the top of three of the boxes, so that the only

light which reaches the cress seeds is colored.

If you are not sure where to get filters from, ask

in a good photographic suppliers or stage lighting

Now, compare the growth of the cress seeds.

shop for colored gelatin. If this does not work,

What seeds seem to be doing well? Why do you

you could always use the clear colored plastic that

think that is?

some sweets are wrapped in, carefully joined with

Chlorophyll in plants is a “photoreceptor.” It is

sticky tape—ensuring that the joins are good and

what converts the light from the sun to food for

no additional light penetrates.

plants to grow. In green plants, there are “chloro-

We have seen in a previous experiment that for the

plasts” which contain chlorophyll—these are green

photosynthesis process to occur, light is an essen-

in color and account for the green coloring of

tial component. We are now going to look at this

plants.

light in a little more detail.

There are two types of chlorophyll, a and b; they

We are going to set up our cress with the light

both respond to similar wavelengths of light, as

and water that they require. However, this time, we

can be seen in Figure 18-7.

are going to have a “control” experiment, and three

You will probably find that the red and blue

other boxes where the sunlight they receive is fil-

filtered plants grew well, whereas the green filtered

tered to “red,” “green,” and “blue.”

plants did not. If you look at Figure 18-8, you will

Take four boxes. Fill the bottom of each one

see that the wavelengths where the “peaks” are

with a layer of 2 cm of cottonwool. Carefully

correspond to the wavelengths of blue and red

pick out 20 cress seeds from the packet for each

colored light.

box, and water them evenly with 5 ml (5 cm3)

The chloroplasts absorb red and blue light,

Project 49: Light-Absorption Properties of Chlorophyll of water.

but reflect green light—that is why we see plants

178

Project 49: Light-Absorption Properties of Chlorophyll

Figure 18-8

Green light as a component of white light.

as green. During the fall/autumn season, the photo-

synthesis activity decreases and the level of chloro-

phyll drops—that is why we see the leaves turn

from green to reds and orange!

Factoid

Remember that we said plants take in carbon

dioxide (CO ), and produce oxygen (O )? Well,

2

2

let’s put some statistics to that assertion! One

hectare, which is just under two and a half acres,

of corn, produces enough oxygen to meet the

requirements of around 325 people!

Biodiesel

At the moment, our cars run on gasoline and diesel

Figure 18-9

Rudolph Diesel.

from deep oil wells. Because we are fast running

out of oil, we see the prices steadily creep up.

We can run compression ignition engines on a

Well, what if oil grew on trees. Well, it might not

wide variety of vegetable oils directly, with a little

grow on trees, but biodiesel certainly comes close!

modification. However, because these oils are quite

Like many of the ideas in this book, it is not a

thick (viscous), problems can be encountered if the

new one. Rudolph Diesel, inventor of the diesel

fuel is cold. For this reason, we take ordinary fuel, and

engine, pictured in Figure 18-9, designed the

turn it into biofuel with a little chemical ingenuity.

original compression ignition engine (that’s diesel

As plants produce their food using

engine to you and me) to run on a wide range of

photosynthesis, biodiesel can be thought of, in a

hydrocarbon fuels. In 1898, Diesel demonstrated

way, as “liquid sunshine” solar energy stored in the

his engine running on peanut oil!

chemical bonds of plants, ready to be used at will.

179

Project 50: Make Your Own Biodiesel

You will need

If you want to know where to get methanol

from, try a good modeller’s shop—as it is often

●

100 ml vegetable cooking oil (corn oil, sunflower

sold as a fuel for model plane engines.

oil, etc.)

●

20 ml methanol

In this experiment, we are going to be making

biodiesel, a fuel that will run in diesel engines, pro-

●

1 g of lye (sodium/potassium hydroxide)

duced from biological matter, in this case vegetable

Tools

oil. It is possible to run an ordinary diesel vehicle

on biodiesel as can be seen in Figure 18-10. Some

●

Glass lab flask, or cylinder

environmentally responsible companies are begin-

ning to run fleets of vehicles on biodiesel.

●

Glass rod to mix

Increasingly, we are seeing blends of biodiesel and

●

Hydrometer

petro-diesel being sold on garage forecourts, and in

●

Safety equipment

●

Eye wash

●

Goggles

●

Gloves

●

Apron

●

Vinegar

Warning

Because of the methanol and the lye used in this

experiment (both of which are toxic and not nice

to handle) this experiment should be carried out

under the supervision of a responsible adult. Lye

is a really strong alkali, which can cause chemical

burns if you are not careful. If you get the dust in

your eye, it can cause permanent damage, even

blindness. You may think that it is an unusual

inclusion for a safety list, but in the event of

spilling any lye, put a spot of vinegar on the lye

to neutralize it and make it safe. The acid will

react with the alkali and produce carbon dioxide.

Make sure you wear all the safety equipment

above and take sensible precautions.

If you are wondering where to get lye from, it

is commonly sold as caustic drain cleaner, but be

aware, it is nasty stuff so take safety precautions.

Project 50: Make Your Own Biodiesel

Figure 18-10

Filling a car with biodiesel.

180

Project 50: Make Your Own Biodiesel

some cases, small quantities of biodiesel are being

added to ordinary diesel as a lubricant.

Online resources

In this project, we are going to make a small

quantity of biodiesel. This experiment aims to

If you want to make biodiesel, you might be

show the process, and illustrate a little bit of the

interested in the following web resources, which

chemistry of manufacturing biodiesel. However,

contain information on manufacturing biodiesel.

please note that there is very little “quality control”

www.schnews.org.uk/diyguide/howtomake

in this experiment, so it would be unwise to use

biodiesel.htm

the produced biodiesel in a diesel engine.

www.veggiepower.org.uk/

First take the vegetable oil and heat it up to

journeytoforever.org/biodiesel_make.html

over 100°C to ensure that any water is driven off.

Be careful not to overheat.

In a separate container, thoroughly mix the

Testing your biodiesel

methanol and lye. This forms a mixture that

biodiesel home brewers call “methoxide,” you

The first test that you will need to conduct is a

need to be very careful during this stage as it

visual inspection—what does your biodiesel

entails using some very nasty chemicals.

look like?

Now add the methoxide to the vegetable oil.

Well, there should be a clear visual distinction

Try and do this at around 45°C for the best

between the top layer and the bottom layer in your

reaction.

measuring container. If there is a large intermedi-

Be careful not to breathe in any of the methanol

ate layer of soaps, then the chances are that you

vapors. If you have access to a fume cupboard in a

did not remove sufficient water from the oil to

school chemistry department, then use that for

begin with.

safety. If not, just make sure you are in a well-

You may be able to get a piece of equipment

ventilated area—outside for example.

called a “hydrometer.” A hydrometer will tell you

Make sure that you thoroughly stir the mixture

the density of a fluid. Your biodiesel should check

for a few minutes.

out with a density of between 880 and 900 grams

Now, put the container somewhere safe, out of

per liter.

the reach of small children, and allow the mixture

to settle overnight.

Biodiesel chemistry

When you next look at the mixture, you should

see that it has settled into two distinct layers. At

So what have we done in this little experiment?

the bottom of the container will be a brown goo.

If you look at Figures 18-11 and 18-12, you will

This is a mixture of glycerol, unused methanol,

see that we have what is called a “triglyceride”

and catalyst, and possibly a little soap, which

molecule. This is the vegetable oil that we start

will be the product of any fatty acids in the oil to

off with. We can represent this using a “ball and

begin with.

stick” model, which shows us the position of the

The layer on top is our biodiesel! Again, I

atoms in 3D space, or we can show the chemistry

reiterate the earlier warning— do not put this in

using a “structural formula” such as that shown in

your vehicle. It will probably work, but this

Figure 18-12.

particular biodiesel has been made with no quality

You will notice when looking at the structure of

control, so there is a high possibility that it could

the triglyceride that there are three long “chains”

damage your engine.

of hydrocarbons (hence the ‘tri’ bit) and a “bacbone,”

181

Figure 18-11

Ball and stick model of a triglyceride.

Figure 18-12

Structural formula of a triglyceride.

Project 50: Make Your Own Biodiesel

182

Project 50: Make Your Own Biodiesel

which links up the three hydrocarbon chains. This

Why do we separate the chains from the glycerol

backbone breaks off from the chains to form

backbone? Well, the structure of the triglyceride

“glycerol,” and this accounts for the “glyceride” bit

means that it can easily become “tangled up” with

of the name.

other triglyceride molecules, which results in a

Our methoxide mixture which was added to our

thick viscous oil. The chains on their own, are a lot

triglycerides catalyzed a reaction where the three

shorter and so tangle less easily, and as a result,

chains broke off from the backbone. The glycerol

are less viscous. This brings with it a whole host of

backbone is heavy, so settles to the bottom of the

other desirable properties, which means that the

jar, whereas the lighter hydrocarbon chains float to

fuel can flow freely in a diesel engine without

the top of the jar—and it is these which form our

clogging up the injectors.

“biodiesel.”

183

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Appendix A

Solar Projects on the Web

Hopefully, this book has provided an interesting

Solar-Powered Wheelchair

primer on solar energy. I rather hope that I have

Bob Triming introduces us to his clean green form

empowered you with the tools to go onwards and

of transport—a solar-powered wheelchair. Flat

create your own solar inventions, powered by clean

batteries are a thing of the past.

green energy. To help you on your way, and

www.infolink.com.au/articles/63/0C044763.aspx

provide inspiration, I have compiled a list of

projects, articles, and inspirational solar tech

Villages in Tanzania Use Solar Power to

stories that I have rooted out for you on the web.

Sterilize Water

This should provide creative inspiration for your

Here is an example of the solar still technology

own sustainably powered designs. All of these sites

seen in this book in action. Villagers are using it to

seem to be particularly interesting or quirky—this

purify their water and prevent illness in Africa.

highlights the need to be creative when finding

news.bbc.co.uk/1/hi/world/africa/4786216.stm

applications for technologies, rather than being

constrained by the dogma of existing applications.

Solar Clothing Monitors Medical

I truly hope they will inspire you, the reader, to go

Conditions

out there and create something truly unique.

Certainly not the coolest looking jacket on the

block, this solar-powered item of clothing monitors

Want Java? Go Solar

medical conditions by using inbuilt sensors.

I’ve seen it all now—a solar-powered coffee

Hopefully, you won’t feel ill in the dark.

roaster! Clean energy when used with fair-trade

www.digitalworldtokyo.com/2006/09/

coffee makes for a guilt-free expresso.

taiwan_puts_ehealth_solar_pane.php

www.makezine.com/blog/archive/

solar_roast_coffee.jpg

Solar-Powered iPod Shuffle

www.solarroast.com/home.html

Powered by a flexible solar cell, Make: show how

to convert an iPod shuffle to run on green power.

Solar-Powered Wiggly Sign

www.makezine.com/blog/archive/2005/03/

In this fantastic site, engineer and cartoonist Tim

solar_powered_i.html

Hunkin builds an interesting piece of kinetic

sculpture, powered by the sun.

Massive Parabolic Solar Death Ray

www.timhunkin.com/a125_arch-windpower.htm

This death ray was built for cooking hot dogs at

the Burning Man event. The scale of this thing is

Humungous Solar-Powered Laundry

totally immense! It is well worth a look.

The world’s biggest laundry employs solar power!

igargoyle.com/archives/2006/07/solar_death_ray_

Read all about how clothes are being washed

for_hot_dogs.html

without the negative environmental connotations at

USA Today.

MIT Solar Generator from Car Junk

www.usatoday.com/tech/news/techinnovations/

In trying to invent a low-cost form of solar energy,

2006-07-30-solar-laundromat_x.htm?csp=34

these academics at the Massachusetts Institute of

185

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Technology showcase their solar generator from

Solar Networking

old auto junk. Recycled green power!

Interesting article about solar-powered wireless

www.technologyreview.com/read_article.aspx?id=

networking in Boulder, Colorado! Is this the

17169&ch=biztech

future of the Internet?

www.internetnews.com/wireless/article.

Solar Water Warmer

php/3525941

A simple and inexpensive design for a solar

water heater. Brought to you by Mother

Solar Death Ray

Earth News.

Another solar death ray, with a cool gallery of

http://www.motherearthnews.com/library/

burnt stuff! Remember kids, if you toast your

1979_September_October/

siblings, your parents may get mad at you.

A_Homemade_Solar_Water_Heater

In addition, note the obligatory: “Do not stare

into the beam directly.”

Sun-Powered Tunes

www.solardeathray.com/

Listen to some music while not having the guilt

of carbon emissions! A solar-powered boom

Solar Bike Light

box—because let’s face it, who wants a party on

Bicycles are already a nice sustainable method

an overcast day?

of transport that do not chuck plumes of carbon

www.makezine.com/blog/archive/2006/05/

dioxide into the air. Well, go one step further,

homemade_solar_powered_boombox.html

rather than powering your lights from batteries

that go in the bin, build a solar-powered bike light.

Solar Sunflower

Genius!

This ’bot, which is essentially a solar tracker,

www.creekcats.com/pnprice/Bike05-Pages/

follows the sun in the same way as sunflowers do.

bikelight.html

Don’t water it though!

www.instructables.com/id/

Solar Greenhouse

E8UMC79GJAEP286WF5/

A nice page about the joys of adding a solar

greenhouse to the side of a dwelling.

Organic LEDs Generate Power

www.theworkshop.ca/energy/grnhouse/

Organic LEDs—a term you are going to hear

grnhouse.htm

about a lot more in the future! As well as

producing light from electricity, these clever little

Solar-Powered Handbag

gadgets also have the potential to produce power

One for the girls, a solar-powered handbag,

from light.

designed by a smart student from Brunel

www.ecogeek.org/content/view/242/

University, U.K. The solar panel charges a

battery, which powers a lining, which glows

Solar Scooter Provides Sustainable

when the bag is opened. Never lose your keys

Transport

again! Louis Vuitton nothing!

A home-built solar-powered scooter, which during

news.bbc.co.uk/2/hi/technology/4268644.stm

a last look at its odometer had clocked up near to

1,000 miles. Scoot on!

Passive Solar Collector

www.treehugger.com/files/2005/09/

A nice passive solar collector made from wholly

diy_eco-tech_ti.php

recycled materials.

www.theworkshop.ca/energy/collector/collector.htm

Solar Projects on the Web

186

Solar Projects on the Web

Solar Ant-Zapper

Solar Ferry for Hyde Park

Possibly cruel (that’s my disclaimer to avoid letters

A solar-powered ferry for the Serpentine in Hyde

from the American Humane Association) but this

Park, London, U.K. How novel! Forty-eight foot

solar-powered ant-zapper could be the answer to

long with 27 panels on its roof.

your infestation woes.

www.usatoday.com/tech/science/

www.americaninventorspot.com/

2006-07-18-solar-ferry_x.htm?csp=34

backyard_solar_energy

Solar-Powered Backpack

Organic Solar Cells Based on Biological

Charge your laptop with the power of the sun

Mechanisms

while trekking up Everest! Now we have heard it all

We read in Chapter 18 all about the process of

www.rewarestore.com/product/020010003.html

photosynthesis, but how about organic solar cells

which mimic the processes that plants use to

Sun Bricks

produce energy. Interesting!

An interesting concept, solar-powered bricks that

www.abc.net.au/science/news/stories/s1729572.htm

incorporate light emitting diodes to provide

illumination at night—a novel idea!

Honda Prius Supplements Power with Solar

www.gardeners.com/on/demandware.store/Sites-

A modified Honda Prius, which uses solar power

Gardeners-Site/default/ViewProductDetail-

to supplement the juice in the car’s batteries to

SellPage?OfferID=35-945&SC=xnet8102

bring an increase in economy!

www.treehugger.com/files/2005/08/

Proposed Solar Chimney Down Under

solar-powered_t.php

This massive solar chimney has been proposed to

generate power in Australia, using a large

Solar-Powered Light Graffiti

greenhouse to heat air, and a solar thermally driven

For miscreants who like to tag, here is the perfect

process. All of 1,600 ft tall!

substitute, which does no damage, and uses clean

money.cnn.com/2006/08/01/technology/

renewable energy to make its mark.

towerofpower0802.biz2/index.htm?cnn=yes

rdn.cwz.net/archives/17

www.enviromission.com.au/project/technology.htm

Holographic Solar Cells

Nanosolar—Printed Solar Cells

Read about holographic solar cells, which use a

If Google founders Larry Page and Sergey Brin

holographic optical element to concentrate the

stick their cash here, you can bet that it is big

frequencies that matter!

business. Nanosolar are a new venture who aim to

www.prismsolar.com/

produce lots of cheap solar cells using simple

printing technology.

Top 10 Strangest Solar Gadgets

nanosolar.com/index.html

This blog provides some interesting thought-

provoking ideas—the top 10 strangest solar

gadgets. Will you invent number 11?

www.techeblog.com/index.php/tech-gadget/

top-10-strangest-solar-gadgets

187

Appendix B

Supplier’s Index

Tampa Bay, FL

Miscellaneous

Tel: 1-727-230-9995

Fort Worth, TX

Alternative Energy Hobby Store

Tel: 1-817-350-4667

Dennis Baker

San Diego, CA

49732 Chilliwack Central RD

Tel: 1-858-605-1727

Chilliwack BC, V2P 6H3

www.siliconsolar.com/solar-books.php

Canada

Tel: 1-604-819-6353

Solar Electric Light Fund

Fax: 1-604-794-7680

1612 K Street, NW Suite 402

Dennis@AltEnergyHobbyStore.com

Washington DC 20006

www.altenergyhobbystore.com/

USA

Education_solar_books.htm

Tel: 1-202-234-7265 (8:30 am–6 pm EST)

info@self.org

Arizona Solar Center

www.self.org/books.asp

c/o Janus II—Environmental Architects

4309 E. Marion Way

Drinking birds for solar engines

Phoenix AZ 85018

USA

The Drinking Bird

solar@azsolarcenter.com

Tel: 1-800-296-5408

www.azsolarcenter.com/bookstore/reviews.html

www.thedrinkingbird.com/

Centre for Alternative Technology Mail

HobbyTron.com

Order

1053 South 1675 West

Machynlleth

Orem UT 84058

Powys

USA

SY20 9AZ

Tel: 1-801-434-7664

UK

Toll-free: 1-800-494-1778

www.hobbytron.com/.html

Kentucky Solar Living

Tel: 1-859-200-5516

Niagara Square

kentuckysolar@ipro.net

7555 Montrose Road

Niagara Falls ON, L2H 2E9

Silicon Solar

Canada

Direct Sales

Tel: 1-905-354-7536

Tel: 1-800-653-8540 (Mon–Fri 8 am–4 pm EST)

Fax: 1-905-354-7536

Fax: 1-866-746-5508

188

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Supplier’s Index

Science eStore

5318 E 2nd Street #530

Fresnel lenses and parabolic

Long Beach CA 90803

mirrors

USA

http://www.physlink.com/eStore

Alltronics

1-888-438-9867

PO Box 730

11am -8pm EST

Morgan Hill CA 95038-0730

USA

Tel: 1-408-778-3868

Electronic components for the

www.alltronics.com

projects in this book

Anchor Optical Surplus

Electromail/RS Components

101 East Gloucester Pike

RS Components Ltd

Barrington NJ 08007-1380

Birchington Road, Corby

USA

Northants NN17 9RS

Fax: 1-856-546-1965

UK

Orderline: 44-(0)-8457-201201

Edmund Optics Inc.

www.rswww.com

101 East Gloucester Pike

Barrington NJ 08007-1380

Maplin Electronics Ltd

USA

National Distribution Centre

Tel: 1-800-363-1992

Valley Road

Fax: 1-856-573-6295

Wombwell, Barnsley

South Yorkshire S73 0BS

Science Kit & Boreal Laboratories

UK

777 E. Park Drive

www.maplin.co.uk

PO Box 5003

Tonawanda NY 14150

Radio Shack

USA

300 RadioShack Circle

Tel: 1-800-828-7777

MS EF-7.105

Fax: 1-800-828-3299

Fort Worth TX 76102

www.sciencekit.com

USA

Tel: 1-800-843-7422

TEP

International Manufacturing Centre

Rapid Electronics Ltd

University of Warwick

Severalls Lane

Coventry CV4 7AL

Colchester

UK

Essex CO4 5JS

UK

Tel: 44-(0)-1206-751166

Inverters and power

Fax: 44-(0)-1206-751188

regulators

sales@rapidelec.co.uk

www.rapidelectronics.co.uk/

Omnion Power Engineering

2010 Energy Drive

PO Box 879

189

East Troy WI 53120

USA

Photovoltaic modules

Tel: 1-262-642-7200 or 1-262-642-7760

Advanced Photovoltaics Systems

www.sandc.com/omnion/home.htm

PO Box 7093

Princeton

Real Goods

NJ 08543-7093

360 Interlocken Blvd, Ste 300

USA

Broomfield CO 80021-3440

Tel: 1-609-275-0599

13771 So. Highway 101

PO Box 836

BP Solar International

Hopland CA 95449

PO Box 191, Chertsey Road

USA

Sunbury-on-Thames

Tel: 1-800-919-2400

Middlesex TW16 7XA

www.realgoods.com

UK

Tel: 44-(0)-1932-779543

Photochemical solar cell

Fax: 44-(0)-1932-762533

components

Kyocera

ICE, the Institute for Chemical Education

8611 Balboa Avenue

University of Wisconsin-Madison

San Diego CA 92123

Department of Chemistry

USA

1101 University Avenue

Tel: 1-619-576-2647

Madison WI 53706-1396

USA

Siemens Solar Industries

Tel: 1-608-262-3033 or 1-800-991-5534

PO Box 6032

Fax: 1-608-265-8094

Camarillo CA 93010

ICE@chem.wisc.edu

USA

Tel: 1-805-698-4200

Photovoltaic cells for buildings

Solarex Corporation

Flagsol

630 Solarex Court

Flachglas Solartechnik GmBH

Fredrick MD 21701

Muhlengasse 7

USA

D-50667 Cologne

Tel: 1-301-698-4200

Germany

Tel: 49-(0)-221-257-3811

Solec International

Fax: 49-(0)-221-258-1117

52 East Magnolia Boulevard

Burbank CA 91502

Schüco International

USA

Whitehall Avenue, Kingston

Tel: 1-213-849-6401

Milton Keynes MK10 0AL

UK

Tel: 44-(0)-1908-282111

Fax: 44-(0)-1908-282124

Supplier’s Index

190

Supplier’s Index

Singapore 428769

Solar array structures, mounting

Tel: 65-65-68966

hardware

Fax: 65-623-44589

www.scienceconnection.com/Tech_advanced.htm

Kee Industrial Products Inc.

100 Stradtman Street

Wattsun

Buffalo NY 14206

Array Technologies Inc.

USA

3312 Stanford NE

Tel: 1-716-896-4949

Albuquerque NM 87107

Toll-free: 1-800-851-5181

USA

Fax: 1-716-896-5696

Tel: 1-505-881-7567

info@keeklamp.com

Fax: 1-505-881-7572

sales@wattsun.com

Kee Klamp GmbH

www.wattsun.com

Voltenseestrasse 22

D-60388 Frankfurt/Main

Zomeworks

Germany

PO Box 25805

Tel: 49-(0)-6109-5012-0

1011A Sawmill Road

Fax: 49-(0)-6109-5012-20

Albuquerque NM 87125

vertrieb@keeklamp.com

USA

Tel: 1-800-279-6342 or 1-505-242-5354

Kee Klamp Limited

Fax: 1-505-243-5187

1 Boulton Road

zomework@zomeworks.com

Reading

Berks RG2 0NH

Solar controllers/temperature

UK

monitors/instrumentation

Tel: 44-(0)-118-931-1022

Fax: 44(0)-118-931-1146

HAWCO Ltd, Industrial Sales

sales@keeklamp.com

The Wharf, Abbey Mill Business Park

Leveleg

Lower Eashing

8606 Commerce Ave

Surrey GU7 2QN

San Diego CA 92121-2654

UK

USA

Tel: 44-(0)-870-850-3850

Tel: 1-619-271-6240

Fax: 44-0)-870-850-3851

sales@hawco.co.uk

Poulek Solar Ltd

Velvarska 9

Raydan Ltd.

CZ-16000 Prague

The Sussex Innovation Centre

Czech Republic

Science Park Square

Tel: 42-(0)-603-342-719

Falmer, Brighton

Fax: 42-(0)-224-312-981

Sussex BN1 9SB

www.solar-trackers.com

UK

Tel: +44-(0)-1273-704442

Science Connection

Fax: +44-(0)-1273-704443

50 East Coast Road, #02-57

sales@raydan.com

191

Solar pool-heater manufacturers

Places to get more information

Heliocol

American BioEnergy Association

13620 49th Street North

314 Massachusetts Avenue, NE

Clearwater FL 33762

Suite 200

USA

Washington DC 20002

Tel: 1-727-572-6655 or 1-800-79-SOLAR

USA

(1-800-797-6527)

www.biomass.org

http://www.heliocol.com/

American Council for an Energy Efficient

Imagination Solar Limited

Economy

10–12 Picton Street

1001 Connecticut Avenue, Suite 801

Montpelier

Washington DC 20036

Bristol BS6 5QA

USA

UK

www.aceee.org

Tel: 44-(0)-845-458-3168

Fax: 44-(0)-117-942-0164

American Solar Energy Society (ASES)

enquiries@imaginationsolar.com

2400 Central Avenue, Suite G-1

Boulder CO 80301

Solar Industries Solar Pool Heating

USA

Systems

Tel: 1-303-442-3130

1940 Rutgers University Boulevard

Fax: 1-303-443-3212

Lakewood NJ 08701

ases@ases.org

USA

www.ases.org

Tel: 1-800-227-7657

Fax: 1-732-905-9899

California Energy Commission

www.solarindustries.com/

1516 Ninth Street

Sacramento CA

Solar Twin Ltd

USA

2nd Floor, 50 Watergate Street

Tel: 1-958-145-512, 1-800-555-7794, or

Chester CH1 2LA

1-916-654-4058

UK

www.energy.ca.go

Tel: 44-(0)-1244- 403407

hi@solartwin.com

Center for Excellence in Sustainable

http://www.solartwin.com/pools.htm

Development

US Department of Energy, Denver Regional Office

Solar robotics supplies

1617 Cole Boulevard

Golden CO 80401

Solarbotics Ltd

USA

201 35th Ave NE

Fax: 1-302-275-4830

Calgary AB, T2E 2K5

Canada

Energy Efficiency and Renewable Energy

Tel: 1-403-232-6268

Clearinghouse (EREC)

Supplier’s Index N. America toll-free: 1-866-276-2687

PO Box 3048

Merrifield VA 22116

192

Supplier’s Index

USA

North Carolina Solar Center

Tel: 1-800-DOE-EREC or 1-800-363-3732

Box 7401

Fax: 1-703-893-0400

North Carolina State University

Doe.erec@nciinc.com

Raleigh NC 27695-7401

USA

Florida Solar Energy Center (FSEC)

Tel: 1-800-33-NCSUN

1679 Clearlake Road

Fax: 1-919-515-5778

Cocoa FL 32922

ncsun@ncsu.edu

USA

www.ncsc.ncsu.edu

Tel: 1-407-638-1000

Fax: 1-407-638-1010

Northeast Sustainable Energy Association

info@fsec.ucf.edu

50 Miles Street

www.fsec.ucf.edu

Greenfield MA 01301

USA

Home Power Magazine

PO Box 520

Rocky Mountain Institute

Ashland OR 97520

1739 Snowmass Creek Road

USA

Snowmass CO 81654-9199

Tel: 1-800-707-6585

USA

www.homepower.com

Sandia National Laboratory—California

NASA Earth Solar Data

PO Box 969

eosweb.larc.nasa.gov/sse/

Livermore CA 94551

USA

National Biodiesel Board

Tel: 1-925-294-2447

3337a Emerald Lane

Sandia National Laboratory—New Mexico

PO Box 104898

PO Box 5800

Jefferson City MO 65110-4898

Albuquerque NM 87185

USA

USA

Tel: 1-505-844-8066

National Center for Appropriate Technology

webmaster@sandia.gov

3040 Continental Drive

www.sandia.gov

Butte MT 59701

USA

Solar Electric Light Fund

Tel: 1-406-494-4572

1612K Street NW, Suite 402

Washington DC 20006

National Renewable Energy Laboratory

USA

1617 Cole Boulevard

Golden CO 80401-3393

USA

Tel: 1-303-275-3000

webmaster@nrel.gov

www.nrel.gov

193

Solar Energy Industries Association

Solar Energy International

1111 N. 19th Street

PO Box 715

Suite 260

Carbondale CO 81623

Arlington VA 22209

USA

USA

Tel: 1-970-963-8855

Tel: 1-703-248-0702

Fax: 1-970-963-8866

Fax: 1-703-248-0714

sei@solarenergy.org

info@seia.org

www.seia.org/Default.htm

Supplier’s Index

194

Index

Page numbers for tables and figures are given in bold

A

F

AC (alternating current), 100, 102, 102

fossil fuels, 2

air conditioning, 39, 41

emissions, 2–3, 4

albedo radiation, 99, 99

and energy in the U.S., 7

alternating current (AC), 100, 102, 102

sources of, 2–3, 5, 6, 15

Archimedes, 61

See also carbon dioxide; Hubbert’s Peak theory; Peak Oil

Fresnel lens, 72–73, 72, 73

sources, 72–73, 189

B

See also solar concentrator

BEAM (Biology, Electronics, Aesthetics, and Mechanics)

Fritts, Charles, 81

robotics, 150, 159. See also solar robotics

fuel cell, 161–162, 163, 164–165, 165

Becquerel, Edmund, 81

mechanics of, 162–164, 168–170, 168, 169, 170

biodiesel, 13, 171, 176, 179–181, 183

types of, 162, 163

biofuel, 171–173, 171, 172, 174–177, 179–181

limitations of, 175–176

G

biomass, 6, 6, 13, 38, 173. See also biofuel biomimickry, 105

Gasohol, 172. See also ethanol

Gratzel, Michael, 105

C

H

carbon dioxide, 3, 173–174

heating

sequestration, 167

of food ( see solar cooking)

chlorophyll, 178–179, 178

solar ( see solar heating)

climate change, 5

space, 1, 1 ( see also solar heating)

coal, 2–3, 34, 66, 173, 174. See also carbon dioxide of water, 1, 1 ( see also solar heating: for hot water) collector. See solar collector

heliodon, 22–25, 24, 25, 26

compression ignition engine, 179

Hubbert’s Peak theory, 3–4, 4

cooking, 1, 1. See also solar cooking

hydrocarbon, 2, 171, 173

hydro-electric power, 6, 6, 7–8, 13

D

hydrogen, generation of, 164–167. See also hydrogen economy

DC (direct current), 100, 102, 102–103

hydrogen economy, 161–162, 168–170

Diesel, Rudolph, 179, 179

hydrological cycle, 55, 55

diesel engine, 176, 179. See also biodiesel hydropower. See hydro-electric power

direct current, 100, 102, 102–103

I

E

industrial revolution, 3, 149, 174

internal combustion engine, 174–175

Einstein, Albert, 81

fuel cells vs., 162

electrical power, 1, 34. See also hydro-electric power; See also steam engine

hydrogen economy; nuclear power; photochemical

International Energy Agency, 4

solar cell(s); solar photovoltaic cell(s);

inverter, 102, 102

wind power

electricity. See electrical power

energy

M

consumption, domestic, 1, 1

Mouchot, Augustin, 8, 55, 66, 67

non-renewable sources of ( see fossil fuels )

nuclear ( see nuclear power)

N

solar ( see solar energy)

nuclear power, 4–5, 7, 7

See also hydro-electric power; hydrogen economy; nuclear power; photochemical solar cell(s); solar photovoltaic

cell(s); wind power

O

ethanol, 171–173, 172, 174–175

Ohl, Russell, 81

195

Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Otto, Nikolaus, 174–175, 175

solar heating ( cont. )

oxygen, from plants, 174, 179. See also photosynthesis

of homes, 28

for hot water, 28–29, 29

P

passive, 28

for power generation, 34, 35

Peak Oil, 3–4, 4

roof panels ( see solar collector: flat plate)

photobiological solar cell(s), 111

of swimming pools, 33–34, 34

photochemical solar cell(s), 105–110, 106

solar ice-maker, 42–43, 43, 44

future of, 110

solar panel. See solar collector: flat plate

limitations of, 110

solar phone charger, 120–122, 122

photosynthesis, 38, 171–174, 171, 172, 174, 176–179

solar photovoltaic cell(s), 81, 105

production of hydrogen by, 167

current-voltage characteristics, 92–94, 92, 93, 94

photovoltaics. See solar photovoltaic cell(s)

crystalline, 82–87, 82, 83, 84

Project Ingenhousz, 111

for driving pumps, 29, 75, 75, 79

and homes, 100, 101, 102–103

S

light sources and, 94–99, 95, 96, 97, 98, 99

thin-film, 83, 83, 87–91, 91

seasons, 12, 12, 13, 17, 19, 19, 21–22

solar pump, 75–79, 76, 78

sequestration, 167

solar radio, 123–124, 123, 124

silicon, 82, 83, 82, 84, 85–86, 86. See also solar

solar robotics, 150, 151, 152, 152–159

photovoltaic cell(s): crystalline

solar still, 55–59, 56, 57, 58, 59, 185

solar battery charger, 119–120, 120

solar torch, 124–125, 125, 126

solar cell

solar tracker, 129–132, 129, 130, 131, 132, 133

photobiological, 111

solar transport

photochemical ( see photochemical solar cell(s))

aviation, 145, 146, 146–148, 147, 148

photovoltaic ( see solar photovoltaic cell(s))

cars, 136–143, 136, 137, 138, 186

solar clock, 17, 18, 20–21

ferry, 187

solar collector, 61, 186

scooter, 186

angle of sun and, 25–26

wheelchair, 185

evacuated tube, 30, 30

solar warning light, 126–127, 127

flat plate, 27, 30–32, 30, 31, 32, 33, 129 ( see also solar tracker)

steam engine, 113, 174

See also solar concentrator

steam reforming, 167

solar concentrator, 61, 62, 63, 64, 64–66, 65, 66

sun, 9, 9–10

Fresnel lens, 72–74, 74

and the earth, 12, 12, 17–21

parabolic dish, 66–67, 67, 68, 69–70, 70, 71

energy from ( see solar energy)

See also solar death ray

structure of, 10, 10–11

solar cooker, 50–53, 51

surface of, 11, 11–12

camping stove, 51–52, 52

See also photosynthesis; solar heating

coffee roaster, 185

sundial. See solar clock

hot dog, 46–47, 47, 185

marshmallow melter, 48, 48

solar cooking, 45, 45, 49, 49, 52–54

T

recipes for, 53–54

thermosiphon, 28, 35

See also solar cooker

tidal power, 7, 13

solar cooling

titanium dioxide, 105, 107

active, 41–44, 43, 44

transportation, 135. See also solar transport passive, 39–41

triglyceride, 181, 182

solar death ray, 61, 63, 64–66, 185, 186

Trombe wall, 39–40, 40, 41

solar distillation. See solar still

solar-driven energy. See biomass; hydro-electric power; wave U

power; wind power

United States

solar energy

energy sources, 2, 7, 7

advantages of, 2, 5

solar energy in, 2, 7, 34, 186

capturing, 14, 15, 17, 19–22, 25–26 ( see also solar-driven energy) devices ( see solar energy: capturing)

limitations of, 161

W

in the U.S., 2, 7, 34, 186

water

solar engines, 113–116, 116, 117, 118, 139

distillation of ( see solar still)

solar garden light, 127–128, 128

pumping of ( see solar pump)

solar heating, 27–28

wave power, 6, 7, 13

circuits for, 35–37, 36

wind energy, 6, 6–7, 13

Index

future of, 37–38

wind power, 6, 6–7, 13

196

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Table of Contents

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Chapter 9

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Chapter 14

Chapter 15

Chapter 16

Chapter 17

Chapter 18