Baixe Solary Energy Projects for the Evil Genius e outras Notas de estudo em PDF para Engenharia Elétrica, somente na Docsity! Ju RIMAS Ch AR RED THE SO BUILD-IT-YOURSELF PROJECTS E - Dm e A DE N A E NAS * Projects include solar heating, cooking, robots, engines, and more a SUTIS ED schematics, and clear instructions * Includes money=saving coupons for TAB PRP e Rs a pe] = GAVIN D.J. HARPER roreworo ey WILLIE NELSON Solar Energy Projects for the Evil Genius Copyright © 2007 by The McGraw-Hill Companies, Inc. All rights reserved. Manufactured in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data- base or retrieval system, without the prior written permission of the publisher. 0-07-150910-0 The material in this eBook also appears in the print version of this title: 0-07-147772-1. 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If you’d like more information about this book, its author, or related books and websites, please click here. Professional Want to learn more? v To the late Mr. P. Kaufman who never failed to make science exciting viii C o n t e n t s 13 Solar Electrical Projects 119 Project 32: Build Your Own Solar Battery Charger 119 Project 33: Build Your Own Solar Phone Charger 120 Project 34: Build Your Own Solar-Powered Radio 123 Project 35: Build Your Own Solar-Powered Torch 124 Project 36: Build Your Own Solar- Powered Warning Light 126 Project 37: Build Your Own Solar- Powered Garden Light 127 14 Tracking the Sun 129 Project 38: Simple Solar Tracker 130 15 Solar Transport 135 Project 39: Build Your Own Solar Car 137 Project 40: Hold Your Own Solar Car Race 142 Project 41: Souping Up Your Solar Vehicle 143 Project 42: Supercharge Your Solaroller 143 Project 43: Build Your Own Solar Airship 146 16 Solar Robotics? 149 Project 44: Assembling Your Photopopper Photovore 153 17 Solar Hydrogen Partnership 161 Project 45: Generating Hydrogen Using Solar Energy 164 Project 46: Using Stored Hydrogen to Create Electricity 168 18 Photosynthesis—Fuel from the Sun 171 Project 47: Proving Biofuel Requires Solar Energy 177 Project 48: Proving Biofuel Requires Water 177 Project 49: Looking at the Light- Absorption Properties of Chlorophyll 178 Project 50: Make Your Own Biodiesel 180 Appendix A: Solar Projects on the Web 185 Appendix B: Supplier’s Index 188 Index 195 Gavin Harper’s book Solar Energy Projects for the Evil Genius is a “must read” for every sentient human on this planet with a conscience, a belief in the bottom line, or a simple belief in the future of humanity. At a time when such a book should be offered as suggested reading for the 19-year-old Gavin Harper, he’s bucking the trend by actually being the author. Okay, so he’s written a book on solar energy you say, big deal you say. You would be wrong. Not only is this Gavin’s fourth book, it is nothing short of pure genius. To be able to write about solar energy is one thing. But to possess the ability to put the knowledge of solar energy into layman’s terms, while including examples of do-it-yourself projects which make the practical applications obvious, gives this boy genius the “street cred” (industry savvy) he so very much deserves. This is a “how-to” book, which debunks the myth that “these things are decades away,” and, without exception, should be in every classroom under the same sun. So crack this book, turn on your solar light, and sit back for a ride into our “present”… as in “gift” from God. Willie Nelson ix Foreword Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use. x There are always a lot of thank-yous to be said with any book, and this one is no exception. There are a lot of people that I would like to thank immensely for material, inspiration, ideas, and help—all of which have fed in to make this book what it is. First of all, a tremendous thank-you to the staff and students of the MSc. Architecture: Advanced Environmental & Energy Studies course at the Centre for Alternative Technology, U.K. I never cease to be amazed by the enthusiasm, passion, and excitement members of the course exude. I’d like to say a big thank-you to Dr. Greg P. Smestad, for his help and advice on photochemical cells. Dr. Smestad has taken leading-edge research, straight from the lab, and turned it into an accessi- ble experiment that can be enjoyed by young sci- entists of all ages. I would also like to thank Alan Brown at the NASA Dryden Flight Research Center for the information he provided on solar flight for Chapter 15. Also a big thank-you to Ben Robinson and the guys at Dulas Ltd. for their help in procuring images, and for setting a great example by show- ing how companies can be sustainable and ethical. I’d also like to thank Hubert Stierhof for sharing his ideas about solar Stirling engines, and Jamil Shariff for his advice on Stirling engines and for continuing to be inspirational. Thanks also to Tim Godwin and Oliver Sylvester-Bradley at SolarCentury, and to Andrew Harris at Schuco for sharing with me some of their solar installations. An immense thank-you to Dave and Cheryl Hrynkiw and Rebecca Bouwseman at Solarbotics for sharing their insight on little solar-powered critters, and for providing the coupon in the back of the book so that you can enjoy some of their merchandise for a little less. A massive thank-you to Kay Larson, Quinn Larson, Matt Flood, and Jason Burch at Fuelcellstore.com for helping me find my way with fuel cells, and for being inspirational and let- ting me experiment with their equipment. It would also be wrong not to mention H2 the cat, who was terrific company throughout the process of learning about fuel cells. Also, many thanks to Annie Nelson, and Bob and Kelly King of Pacific Biodiesel for providing me with some amazing opportunities to learn about biodiesel. Thanks to Michael Welch at Home Power magazine, and also to Jaroslav Vanek, Mark “Moth” Green, and Steven Vanek, the designers of the fantastic solar ice-maker featured in Chapter 5. Their solar-powered ice-maker has already proven its immense worth in the developing world … and if you guys at home start building them at home and switching off your air-con and freezers, they stand to be a big hit in the developed world as well. A big thank-you to my grandfather, who has seen the mess upstairs and manages to tolerate it, to my grandmother who hears about the mess upstairs and does not realize its magnitude, and to Ella who does a good job of keeping the mess within sensible limits—and knows when to keep quiet about it. Thanks are also long overdue to my dad, who is always immensely helpful in providing practical advice when it comes to how to build things, and to my mum who manages to keep life going when I have got my head in a laptop. A huge thank-you to Judy Bass, my fantastic editor in New York who has been great throughout the trials and tribulations of bringing this book to print, and to the tremendous Andy Baxter (and the rest of his team at Keyword) who has managed to stay cool as a cucumber and provide constant reas- surance throughout the editing process. Acknowledgments Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use. So where did all these fossil fuels come from . . . and can’t we get some more? OK, first of all, the answer is in the question— 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 which in turn was part of the Paleozoic era, around 360 to 286 million years ago. This would have been an interesting time to live—the world was covered in lots and lots of greenery, big ferns, lush verdant forests of plants. The oceans and seas were full of algae—essentially lots of small green plants. Although there are some coal deposits from 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. So what happened to make the fossil fuels? Well, the plants died, and over time, layers of rock and sediment and more dead stuff built up on top of these carbon-rich deposits. Over many years, the tremendous heat and pressure built up by these layers compressed the dead matter We have only recently started to worry about fossil fuels—surely we have time yet? This is an incorrect assumption. For some time, people have prophesized the end of the fossil fuel age. When the Industrial Revolution was in full- swing Augustin Mouchout wondered whether the supply of fossil fuels would be able to sustain the Industrial Revolution indefinitely. “Eventually industry will no longer find in Europe the resources to satisfy its prodigious expansion. Coal will undoubtedly be used up. What will industry do then?” Fossil fuel emissions Take a peek at Figure 1-3. It is pretty shocking stuff! It shows how our fossil fuel emissions have increased dramatically over the past century—this massive amount of carbon dioxide in the atmos- phere has dire implications for the delicate balance of our ecosystem and could eventually lead to run- away climate change. Hubbert’s peak and Peak Oil Back in 1956 an American geophysicist by the name of Marion King Hubbert presented a paper to the American Petroleum Institute. He said that oil production in the U.S.A. would peak toward the end of the 1960s, and would peak worldwide in the year 2000. In fact, U.S. oil production did peak at 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 follows a bell-shaped curve, where production begins to gradually increase, then as the technol- ogy becomes mainstream there is a sharp upturn in production, followed by a flattening off when pro- duction has to continue against rising costs. As the costs of extraction increase, production begins to plateau, and then fall—falling sharply at first, and then rapidly. 3 W h y S o l a r ? This is illustrated in Figure 1-4. This means that, if we have crossed the peak, our supplies of fossil fuels are going to begin to drop rapidly—when you think about how reliant we are on fossil fuels, this means that there is going to be a rapid impact on our way of life. So have we crossed the peak, and is there any evidence to support this? 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 which uranium is consumed will greatly increase. 4 W h y S o l a r ? Figure 1-3 How our fossil fuel emissions have increased. Figure 1-4 Depiction of the “Peak Oil” scenario. A few other reasons why nuclear is a dumb option Nuclear power really is pretty dangerous—talking about nuclear safety is a bit of a myth. Nuclear power stations are a potential target for terrorists, and if we want to encourage a clean, safe world, nuclear is not the way to go. Nuclear makes bad financial sense. When the fledgling nuclear power industry began to build power stations, the industry was heavily subsi- dized as nuclear was a promising new technology that promised “electricity too cheap to meter.” Unfortunately, those free watts never really materi- alized—I don’t know about you, but my power company has never thrown in a few watts produced cheaply by nuclear power. Solar on the other hand is the gift that keeps on giving—stick some photo- voltaics on your roof and they will pump out free watts for many years to come with virtually zero maintenance. Decommissioning is another big issue—just because you don’t know what to do with some- thing when you finish with it isn’t an argument to ignore it. Would you like a drum of nuclear waste sitting in your garden? All the world round, we haven’t got a clue where to stick this stuff. The U.S.A. has bold plans to create Yucca mountain, a repository for nuclear waste—but even if this hap- pens, the problem doesn’t go away—it is simply consolidated. Environmental responsibility Until cheap accessible space travel becomes a reality, and let’s face it, that’s not happening soon, we only have one planet. Therefore, we need to make the most of it. The earth only has so many resources that can be exploited, when these run out we need to find alternatives, and where there are no alternatives then we will surely be very stuck. Mitigating climate change It is now widely acknowledged that climate change is happening, and that it is caused by man-made events. Of course, there is always the odd scientist, who wants to wave a flag, get some publicity and say that it is natural and that there is nothing we can do about it, but the consensus is that the extreme changes that we are seeing in recent times are a result of our actions over the past couple of hundred years. Sir David King, the U.K.’s Chief Scientific Advisor says that climate change is “the most severe problem that we are facing today—more serious even than the threat of terrorism.” So how can we use solar energy? When you start to think about it, it is surprising how many of the different types of energy sources around us actually come from the sun and solar- driven processes. Take a look at Figure 1-5 which illustrates this. 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 sun. Fossil fuels are the remains of dead animal and plant matter that have been subject to extreme temperature and pressure over millions of years. Those animals fed on the plants that were around at the time (and other animals) and those plants grew as a result of the solar energy that was falling on the earth. 5 W h y S o l a r ? There are limits to how much extra hydroelectric capacity can be built. Hydroelectricity relies on suitable geographic features like a valley or basin 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- scale flooding which must take place to provide the water for the scheme. Micro-hydro offers an interesting alternative. Rather than flooding large areas, micro-hydro schemes can rely on small dams built on small rivers or streams, and do not entail the massive infrastructure that large hydro projects do. While they produce a lot less power, they are an interest- ing area to look at. So all this is new right? Nope . . . Augustin Mouchot, a name we will see a couple of times in this book said in 1879: “One must not believe, despite the silence of modern writings, that the idea of using solar heat for mechanical operations is recent.” 8 W h y S o l a r ? The Solar Resource Chapter 2 The sun Some 92.95 × 106 miles away from us, or for those working in metric 149.6 × 106 km away from us is the sun (Figure 2-1). To imagine the magnitude of this great distance, think that light, which travels at an amazing 299,792,458 meters per second, takes a total of 8.31 minutes to reach us. You might like to do a thought experiment at this point, and imagine yourself traveling in an airplane across America. At a speed of around 500 miles per hour, this would take you four hours. Now, if you were trav- eling at the speed of light, you could fly around the earth at the equator about seven and a half times in one second. Now imagine traveling at that speed for 8.31 minutes, and you quickly come to realize that it is a long way away. Not only is it a long way away, but it’s also pretty huge! It has a diameter of 864,950 miles; again, if you are working to metric standards that equates to 1.392 million km. Although the sun is incredibly far away—it is also tremendously huge! This means that although you would think that relatively little solar energy reaches us, in fact, the amount of solar radiation that reaches us is equal to 10,000 times the annual global energy consumption. On average, 1,700 kWh per square meter is insolated every year. Now doesn’t it seem a silly idea digging miles beneath the earth’s surface to extract black rock and messy black liquid to burn, when we have this amazing energy resource falling on the earth’s surface? As the solar energy travels on its journey to the earth, approximately 19% of the energy is absorbed by the atmosphere that surrounds the 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 helium, minute by minute, second by second. 9 Figure 2-1 The sun. Image courtesy NASA. Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use. But what stops the sun from exploding in a massive thermonuclear explosion?—simple gravity! The sun is caught in a constant struggle between wanting to expand outwards as a result of the energy of all the complex reactions occurring inside it, and the massive amount of gravity as a result of its enormous amount of matter, which wants to pull everything together. All of the atoms inside the sun are attracted to each other, this produces a massive compression which is trying to “squeeze” the sun inwards. Meanwhile, the energy generated by the nuclear reactions taking place is giving out heat and energy which wants to push everything outwards. Luckily for us, the two sets of forces balance out, so the sun stays constant! Structure of the sun Figure 2-2 illustrates the structure of the sun—now let’s explain what some of those long words mean! Starting from the center of the sun we have the core, the radiative zone, the convective zone, the photosphere, the chromosphere, and the corona. The core The core of the sun possesses two properties which create the right climate for nuclear fusion to occur—the first is incredibly high temperature 15 million degrees Celsius (I don’t envy the poor chap who had to stand there with a thermometer to take the reading) and the second is incredibly high pressure. As a result of this nuclear fusion takes place. In nuclear fusion, you take a handful of hydro- gen nuclei—four in fact, smash them together and end up with one helium nucleus. There are two products of this process—gamma rays which are high-energy photons and neutrinos, one of the least understood particles in the uni- verse, which possess no charge and almost no mass. 10 T h e S o l a r R e s o u r c e Figure 2-2 The structure of the sun. Image courtesy NASA. Solar power Solar-powered devices are the most direct way of capturing the sun’s energy, harnessing it, and turning it into something useful. These devices capture the sun’s energy and directly transform it into a useful energy source. Wind power The heat from the sun creates convective currents in our atmosphere, which result in areas of high and low pressure, and gradients between them. The air rushing from place to place creates the wind, and using large windmills and turbines, we can collect this solar energy and turn it into something useful—electricity. Hydropower The sun drives the hydrological cycle, that is to say the evaporation of water into the sky, and precipi- tation down to earth again as rain. What this means is that water which was once at sea level can end up on higher ground! We can collect this water at a high place using a dam, and then by releasing the water downhill through turbines, we can release the water’s gravitational potential energy and turn it into electricity. Biomass Rather than burning fossil fuels, there are certain crops that we can grow for energy which will replace our fossil fuels. Trees are biomass, they produce wood that can be burnt. Sugarcane can also be grown and be turned into bio-ethanol, which can be used in internal combustion engines instead of gasoline. Oils from vegetable plants can in many cases be used directly in diesel engines or reformed into biodiesel. The growth of all of these plants was initiated by the sun in the first place, and so it can be seen that they are derived from solar energy. Wave power Wave power is driven by the winds that blow over the surface of large bodies of water. We have seen how the wind is produced from solar energy; however, we must be careful to distinguish wave power from tidal power, which is a result of the gravitational attraction of the moon on a large body of water. 13 T h e S o l a r R e s o u r c e Figure 2-5 The sun changes position depending on the time of year. 14 T h e S o l a r R e s o u r c e 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. Fossil fuels You probably never thought that you would hear an environmentalist saying that fossil fuels are a form of solar energy—well think again! Fossil fuels are in fact produced from the clean energy of the sun—at the end of the day, all they are is compressed plant matter which over millions of years has turned into oil, gas, and coal—and herein lies the problem. It took millions of years for these to form, and they are soon exhausted if we burn them at their present rate. So yes, they are a result of solar energy, but we must use them with care! As we have seen, there are many ways in which we can harness solar power. Figure 2-6 shows some clean renewable ways in which we can capture solar energy not only from solar panels, but also from the power in the wind. Although not immediately apparent, the black pipeline that runs through the picture is in fact a small-scale hydro installation—yet another instance of solar energy being harnessed (indirectly). This book focuses solely on “directly” capturing solar energy. In Figure 2-7 we can see a variety of technologies being used to capture solar energy directly in a domestic setting. 15 T h e S o l a r R e s o u r c e 18 P o s i t i o n i n g Y o u r S o l a r D e v i c e s Figure 3-1 Cleopatra’s needle—an early solar clock? Figure 3-2 How shadows change with the time of day. The season in the northern hemisphere will be exactly the opposite to that in the southern hemi- sphere at any one time. We can see in Figure 3-3 that because of this tilt, at certain times of year, depending on your latitude you will receive more or less sunlight per day. Also if you look at your latitude relative to the sun, you can see that as the earth rotates your angle to the sun will be different at any given time of day, depending on the season. We can see in Figure 3-4 an example house in the southern hemisphere—here we can see that the sun shines from the north rather than the south . . . obviously if your house is in the northern hemi- sphere, the sun will be in the south! This graphically demonstrates how the sun’s path in the sky changes relative to your plot at different times of year, as well as illustrating how our rules for solar positioning are radically different depending on what hemisphere we are in. What does this mean for us in practice? Essentially, it means that we need to change the position of our solar devices if we are to harness the most solar energy all year round. 19 P o s i t i o n i n g Y o u r S o l a r D e v i c e s Figure 3-3 How the earth’s position affects the seasons. Figure 3-4 Seasonal variation of the sun’s position. 20 P r o j e c t 1 : B u i l d a S o l a r - P o w e r e d C l o c k ! You will need ● Photocopy of Figure 3-5 ● Matchstick ● Glue Tools ● Scissors This is a dead-easy and quick sundial for you to 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.” 23 ● Craft knife ● Protractor For the wooden heliodon ● Bandsaw ● Pillar drill ● Sander ● Protractor We have already seen in this chapter about the sun’s path—and we have learnt how we can use the sun to provide natural lighting and heating. We saw in Figure 3-3 how the position of the sun and the earth influences the seasons, and how the path of the sun in the sky changes with the seasons. This is important to us if we want to design optimal solar configurations, as in order to maximize solar gain, we need to know where the sun is shining! A heliodon is a device that allows us to look at the interaction of the light coming from the sun, and any point on the earth’s surface. It allows us to easily model the angle at which the light from the sun will hit a building, and hence see the angle cast by shadows, and gauge the paths of light into the building. The heliodon is a very useful tool to give us a quick reckoning as to the direction of light coming into the room, and what surfaces in that room will be illuminated at that time and date with that orientation. A heliodon is also very useful for looking at overshadowing—seeing if objects will be “in the way” of the sun. With our heliodon, it is possible to construct scale models that allow us to see, for example, if a certain tree will overshadow our solar panels. The heliodon is therefore a very useful tool for solar design, without having to perform calculations. In this project, we present two separate designs. The first is for a cardboard heliodon, which is simple if you just wish to experiment a little with how the heliodon works. The design requires few materials and only a pair of scissors—but, it may wear out over time. This does not mean that there 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 professionally, for example if you are a professional who will routinely be performing architectural design or using the heliodon for education. Our heliodon will consist of three pieces of board. The first forms a base; on top of this base, we affix a second board which is allowed to swivel by way of, in the wooden version, a “Lazy Susan” bearing. This is a ball-bearing race that you can buy from a hardware shop, which is ordinarily used as a table for a “Lazy Susan” rotating tray. In the cardboard version, we simply use a split leg pin pushed through the center of both sheets, with the legs splayed and taped down. The third board is hinged so that the angle it makes with the horizontal can be controlled, it is also equipped with a stay to allow it to be set at the angle permanently and rigidly. And that is just about it! With the wooden version, a length of piano hinge accomplishes this job admirably, and with the cardboard version, a simple hinge can be made using some strong tape. The other part of the heliodon is an adjustable light source. This can be made in a number of ways. The simplest of which is a small spotlamp equipped with a clip that allows it to be clamped to a vertical object such as the edge of a door. Slide projectors are very good at providing a parallel light source—these present another option if their height can easily be adjusted. If you will be using the heliodon a lot, it would make sense to get a length of wood mounted vertically to a base, with the dimensions given in Table 3-1 marked permanently on the wood. Heliodon experiments Once you have constructed your heliodon you can begin to perform some experiments using it. P r o j e c t 2 : B u i l d Y o u r O w n H e l i o d o n 24 You need to be aware of the three main adjustments that can be made on the heliodon. ● Seasonal adjustment—by moving the lamp up and down using the measurements listed above, it is possible to simulate the time of year. ● Latitude adjustment—by setting the angle that the 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, you can simulate the earth’s rotation on its axis, and simulate different times of day. The two table adjustments are illustrated in Figure 3-7. 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 table, the time on the sundial changes. You can use this approach to calibrate your heliodon. You might like to make some marks on the cardboard surface to indicate different times of day. The next stage of experimentation with the heliodon is to look at modeling a real building. P r o j e c t 2 : B u i l d Y o u r O w n H e l i o d o n Compass points Remember to think carefully about where north and south are in relation to your modeling table. Consider whether the site you are modeling is in the north or south hemisphere and adjust the position of your model accordingly. Figure 3-8 Heliodon sundial experiment. Figure 3-7 Heliodon table adjustments. 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 These measurements are assuming a measurement of 87 in. between the center of the heliodon table and the light source 25 P r o j e c t 3 : E x p e r i m e n t i n g w i t h L i g h t R a y s a n d P o w e r Construct a model from cardboard (Figure 3-9), and include for example, window openings, doors, patio doors, and skylights. By turning the table through a revolution, it is possible to see where the sun is penetrating the building, and what parts of the room it is shining on. This is useful, as it allows us to position elements of thermal mass in the positions where they will receive the most solar radiation. We can also make models of say, a solar array, and cluster of trees, and see how the trees might overshadow the solar array at certain times during the year. Use the heliodon with scale models to devise your own solar experiments! Now with modern computer aided design (CAD) technology, the heliodon can be replicated digitally inside a computer. Architects routinely use pieces of CAD software to look at how light will penetrate their buildings, or whether obstructions will overshadow their solar collectors. However, heliodons are still a very quick, simple technology which can be used to make a quick appraisal of solar factors on a model building. A professional, more durable heliodon can be seen in Figure 3-10. You will need ● Small torch ● Length of string ● Tape ● Big sheet of paper ● Bunch of pencils ● Elastic band Attach the large sheet of paper to the wall using the tape. Then, take the piece of string, and attach 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 the bulb of the torch falls within the boundary of the paper. We are going to see how angle affects the light power falling on a surface when the distance from the surface remains the same. Now imagine our torch as the sun, hold the torch to face the paper directly keeping the string taught. You should see a “spot” of light on the paper. 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. Project 3: Experimenting with Light Rays and Power How does solar heating work? On a hot summer day, if you are walking around a parking lot, gently touch a black car, and the chances are it will feel very hot. Now touch a silver or white car, and you will find that it is significantly cooler. This is the principle that underpins solar heating. A black surface heats up quickly in the sun. Our demand for hot water is driven by a number of things. We use hot water every day for tasks such as washing our hands, clothes and dishes. From now on, we will refer to this as “solar hot water.” We can also use hot water for heating our homes. We will refer to this as “solar space heating” from now on. What we need to do, is look at our demand for heated water, and see how it correlates to the energy available from the sun. Solar hot water Our demand for hot water is fairly constant throughout the year. We use more or less the same amount of hot water for washing and cleaning in the winter as we do in the summer. Solar space heating We can also use solar energy to heat our space directly—passively, rather than using an active system. This is called passive solar design. We can design our buildings with large expanses of glass on the sun-facing façades in order to capture the solar energy and keep the building warm and light. However, the requirements for space heating are different in the winter from in the summer. If we design our buildings for “summer conditions,” they could be intolerably cold in the winter. For this reason, we can use architectural devices such as shading and brie soleil to ensure that the room receives an optimal amount of light in both summer and winter. Passive solar design is a whole book in its own right though! What does a solar heating system look like? Figure 4-1 illustrates a basic solar water heating system. We can see a large storage tank in the Figure. This is filled with water and is used as a thermal store. It is imperative that this tank is incredibly well insulated as it is pointless going to a lot of effort to collect this solar energy if we then lose it in storage! 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. We draw the hot water off from the top of the tank, while replacing the hot water with cold water at the bottom of the tank. This allows us to maintain the “layered” stratified nature of the tank. 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. The pipes are connected in a closed circuit to a solar collector. This closed circuit is filled with a fluid which transfers the heat from the solar cell to the tank. This is the simplest type of solar system—it is called a thermosiphon. The reason for this name is that the process of circulation from the solar cell to the tank is driven by nothing more than heat. Natural convective currents set up a flow, whereby the hot water makes its way around the circuit. It is also possible to insert a pump into this circuit to increase the flow of the heat transfer medium. 28 S o l a r H e a t i n g 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. 29 S o l a r H e a t i n g Figure 4-1 A basic solar water heating system. Figure 4-2 A cutaway of a thermal store tank. 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. 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 absorbs from being transmitted into the roof it is mounted on. A coil of tube within this collects the heat and transmits it to the storage tank, and at the front of the collector is an absorbent surface. This could simply be matt black, or it could be a selective coating. On the roof shown in Figure 4-5 we can see a variety of different solar cells, both thermal and photovoltaic nestling together in harmony. 30 S o l a r H e a t i n g Figure 4-3 Flat plate versus evacuated tube collectors. Figure 4-4 Cutaway of a flat plate collector. While having a pool in your yard is a great way to exercise and enjoy the summer sun, swimming pools are notorious for “drinking” energy. The problem is that there is simply such a great volume of water to heat! Energy is becoming more expensive as we begin to realize the serious limitations of the previously cheap and abundant fossil fuels. Some people heat their pools in order to be able to enjoy them out of season; however, that comes with a big associated energy cost. Before you even start to consider heating your pool using solar energy, you need to consider energy reduction and efficiency measures. You might want to consider your usage patterns. Will it really make much difference to me if I can’t use my pool out of season? After all, who really wants to swim when it is cold and wet outside! Also you might want to consider energy minimization strategies. Is your pool outside and uncovered at the moment? Heat rises . . . so all that heat that you are throwing into your pool is being lost as it dissipates into the atmosphere. This isn’t smart! Building some kind of enclosure over your pool will make the most of any investment that you put into solar heating your pool. Once you have taken steps to minimize the energy that your pool requires, you can begin to make advances toward heating it using free solar energy. There is nothing really too complicated about a solar pool heating system. As we only need to elevate the temperature of the water slightly, we can use simple unglazed reflectors. The reason? Well think of it like this . . . the water you get from the hot tap to wash with is significantly hotter than the sort of temperature you would be expecting to swim in. A domestic solar hot water rig heats a small volume of water to a very high temperature. By contrast, a solar pool heating system, takes a large quantity of water, and heats it by a small amount. Here is the fundamental difference. Because the water is 33 P r o j e c t 5 : S o l a r H e a t Y o u r S w i m m i n g P o o l Project 5: Solar Heat Your Swimming Pool Figure 4-9 A recycled radiator collector. circulating at a faster rate, unglazed collectors can provide acceptable efficiency. But that’s not all! 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 is possible to dump excess heat. This technology isn’t just applicable to small pools at home, large municipal pools are also heated by solar technology in a number of cases. Take for instance the International Swim Center at Santa Clara, California, 13,000 square meters of solar collector heat a total of 1.2 million gallons of water a day! Figure 4-10 illustrates solar pool heating. The Supplier’s Index (Appendix B) lists a number of companies that sell products for solar heating your pool. Do we need to use solar thermal power directly? If we consider power generation on a large scale, all of our power stations whether they be nuclear, coal, oil, or gas fired, all produce heat primarily, and then use this heat to produce steam, which then, through using rotating turbines, produces electricity. This means, that at present, we do not produce 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. Once we recognize this, we quickly realize that it could be possible to use solar thermal energy to raise steam to generate electricity. And this is exactly what they are doing in Kramer Junction, California. Tip Enerpool is a free program that can be used to simulate your swimming pool being heated with solar collectors. By inputting information such as your location, and how the pool is covered. The program can predict what temperature your pool will be at, at any given time! www.powermat.com/enerpool.html 34 P r o j e c t 5 : S o l a r H e a t Y o u r S w i m m i n g P o o l Figure 4-10 Solar pool heating. Although we have discussed basic systems here for producing solar heat—and by no means is this comprehensive coverage of solar heating (the subject really deserves several books in its own right) there are a number of things that we can do to improve our system. If our system is “active,” which is to say if there is a pump driving a working fluid around the system, then we can do a little more to control the fluid. If our system is passive, i.e., a thermosiphoning system, where the fluid makes its way around the system as a result of changes in density, then we might at least like some feedback as to what our system is doing. You will need ● Negative temperature coefficient thermistor ● 2 × 10 k resistor ● 100 k variable resistor ● 741 op amp ● 1 M resistor ● 4.7 k resistor ● BC109 NPN transistor ● 6 V piezo buzzer ● Heatshrink tubing ● Mastic/silicone sealant Optional ● 6 V relay ● Protection diode Tools ● Soldering iron ● Side cutters ● Solder 35 P r o j e c t 6 : U s e f u l C i r c u i t s f o r S o l a r H e a t i n g Project 6: Useful Circuits for Solar Heating Figure 4-11 Solar thermal power in the Mojave desert. Courtesy Department of Energy. of solar energy is seasonal, and in part that deter- mines the supply of solar hot water. Even when the sun cannot provide all of the energy all of the time, or where 100% solar provision would be uneconomical, it can certainly go a long way toward reducing the amount of energy we need to consume. Even pre-heating water a little bit in winter goes some way to saving energy. Another thing that needs careful consideration, is that if we need to provide extra energy for our heating needs, where will that energy come from? Fossil fuels pollute the atmosphere and are a finite resource, nuclear leaves a legacy of toxic waste, but maybe solar energy has another trick up its sleeve—biomass! The trees and plants that we are surrounded by are effectively solar batteries! They take the energy produced from the sun, and using a process called photosynthesis, use the energy to grow. All the time that they are growing, they are taking in carbon dioxide from the atmosphere and producing oxygen. Once a tree has grown, we can cut it down and burn it. While this process releases carbon dioxide into the atmosphere, there is no “net gain” of carbon dioxide, as the tree took the carbon dioxide out of the atmosphere while growing! 38 T h e F u t u r e o f S o l a r H e a t i n g Solar Cooling Chapter 5 In hot climates, it can often become uncomfortably hot—in the modern world, we tend to look toward air conditioning to provide a comfortable internal atmosphere; however, air conditioning often leaves us with dry stale air. While it would seem to be counterintuitive to use the sun to cool things down, there are a number of techniques that we can use to cool things down by employing the sun’s energy. Why air conditioning is bad The amount of energy that air conditioning consumes is truly tremendous. In addition to this, the heat extracted from the building is simply dumped out into the atmosphere. Air conditioning cooling stacks are a breeding ground for Legionella bacteria, and the refrigerants used in air conditioning are ozone-depleting and add to the burden of global warming. While there has been a worldwide move to eliminate CFCs from air conditioning units because of the damage they do, the interim HCFC and HFC chemicals are still not environmentally friendly. What can we do instead? Rather than using large amounts of fossil fuels, there are a number of other strategies that we can use to cool our buildings. Passive solar cooling There are a number of ways that we can design our buildings to stay at a pleasant internal temperature, and prevent them from overheating, even in the summer. 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 (U.S. Patent 246626). However, the idea never really gained much of a following until 1964, when the engineer Felix Trombe and architect Jacques Michel began to adopt the idea in their buildings. As such, this type of design is largely referred to as a “Trombe wall.” Figure 5-1 shows a Trombe wall on one of the resident’s houses at the Centre for Alternative Technology (CAT), U.K. Let’s describe the construction and operation of the Trombe wall. Essentially, the Trombe wall is a wall with a high thermal mass, the wall is painted black to enable it to absorb solar radiation effectively. 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 thermal mass during the day. At night, this heat would be dissipated both into the room—but also to the outside through the air gap and glazing. The theory was that the glazing would help to retain heat, and because the thermal mass had gained enough heat during the day, it would be warmer 39 Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use. than the internal room temperature, as a result, the room would warm up. In reality it appeared that most of the heat was simply dumped to the cold outside. A series of improvements were made to the design of the Trombe wall which significantly increased its performance. In the improved version of the Trombe wall, there are vents at the top and bottom of the wall, and also on the glazing. These vents have a mechanism that allows them to be opened and closed in certain configurations. The general scheme of things is that the sun shines through the glazing, where it heats up the thermal mass of the wall behind. The wall, being of a construction that has a high thermal mass (for example masonry or concrete) transfers some of the heat energy to the air in the gap between the glazing and the wall as it heats up. A convection current is set up. If you are familiar with heat and the way it affects air, you 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 the room. Of course during the summer, this heat isn’t really wanted—so the flaps can simply be closed in order to keep the room cool. But this chapter did say it was about solar cooling! Well, if you also have flaps in the glazing which can be opened and closed, you can then open a flap at the top of the glazing, and at the bottom of the thermal mass. The flap at the top of the thermal mass is closed. This sets up a convective current which sucks air out of the bottom of the room, and heats it slightly, causing it to rise. But rather than this air being fed back into the room, the air is instead dissipated into the outside atmosphere. This has the effect of sucking air from the room. This air has to be replaced somehow, so what happens is that fresh air is sucked in through cracks in the building fabric, gaps in doors and windows, etc. This pro- vides a fresh cooling breeze for the occupants (Figure 5-2). 40 S o l a r C o o l i n g Figure 5-1 Trombe wall at CAT, U.K. suspended from this using U bolts. This allowed the collector to be moved to accommodate seasonal variations. How does the ice-maker work? The ice-maker works on a cycle—during the daytime ammonia is evaporated from the pipe at the focal point of the parabolic mirrors. This is because the sun shines on the collector which is painted black to absorb the solar energy—this collector heats up, driving the ammonia from the salt inside. At night, the salt cools and absorbs the ammonia, as it does this, it sucks it back through the collector. As it evaporates from the storage vessel, it takes heat with it. Warning For the system to operate for long periods of time, the materials used should be resistant to corrosion by ammonia. Steel and stainless steel are ideal in this respect as both are immune to corrosion by ammonia. Another consideration is the pressure under which the system will have to operate. 43 P r o j e c t 7 : S o l a r - P o w e r e d I c e - M a k e r Figure 5-3 Solar cooler layout. Figure 5-4 Solar cooler plumbing details. Figure 5-5 illustrates this cycle. Useful addresses The following addresses may be useful if you wish to make further enquiries about this design of ice-maker: S.T.E.V.E.N. Foundation, 414 Triphammer Rd. Ithaca, NY 14850 U.S.A. SIFAT, Route 1, Box D-14 Lineville, AL 36266 U.S.A. Note This design has a number of strengths which make it robust and reliable in operation. One of those strengths is that the design has an absolute minimum of moving parts. The only things that actively move are the valves—and even these are operated infrequently. The elimination of moving parts makes this design very efficient. 44 Figure 5-5 The solar cooler cycle. P r o j e c t 7 : S o l a r - P o w e r e d I c e - M a k e r Solar Cooking Chapter 6 Why cook using the sun? Solar cooking is a great alternative to conven- tional cooking—rather than burning fuel and producing carbon dioxide emissions, or using precious electricity, solar cooking harnesses the natural energy available from the sun! It is a great social activity on a sunny day—barbe- ques are just sooooo yesterday—solar cooking is where it is at! No fumbling with matches and firelighters, no choking on smoke, no burnt sausages! Just hope that the clouds don’t come! 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 growing and developing, our energy will run out sooner rather than later if everybody wants to live a western lifestyle—but why even should we in the West want to live a western lifestyle when things like solar cooking can be so much fun—and achieve the same ends that conventional cooking does, heating a food product. All of the projects in this chapter can be built very cheaply and are ideal for a fun summer’s day! At the end of this chapter, I have put together a collection of links to various different types of solar cooker plans that are out there on the web— all have different strengths and weaknesses and are suited to different applications, from designs that will just about cook a frankfurter, to large cookers that can be used for community catering! 45 Figure 6-1 A solar cooker being used in the developing world. Image courtesy Tom Sponheim. Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use. You will need ● Marshmallows ● Large Fresnel lens ● Tin foil ● Skewers or a toasting fork In this project, we are going to collect the sun’s energy from a large area, and focus it to a point in order to create localized heating. One way of collecting the sun’s energy from a large area is to use mirrors. We have already explored this in the “solar hot dog cooker.” You will read more about concentrating solar energy in the chapter on Solar Collectors (Chapter 8). In order to perform this experiment, we are going to need a Fresnel lens—again see the chapter 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 lens, to focus the sun’s rays onto the marshmallow. When you look out of your window, there is no magnification or reduction of the image—the glass does not act like a lens; however, you will notice when looking through the Fresnel lens (not at the sun!) the image appears much bigger and magni- fied. Why is this? If you look closely, you will see a series of concentric circles in the Fresnel lens. Now think of a magnifying glass—it is round and circular, and “bulges” in the middle. If we look at the glass from side-on, we can see that both sides of the lens are curved—but there is also a lot of glass in the middle! A Fresnel lens “removes” some of the glass from the middle, and flattens the lens onto a sheet. Each little concentric ring that you see on the flat Fresnel sheet, is a section of lens curve. Look at where the sun is in the sky, and hold the Fresnel lens perpendicular to an imaginary line between the sun and your marshmallow. Move the lens to and fro along this line, and observe how the focused beam of solar energy changes on your marshmallow. After a little bit of time, focusing the sun onto the marshmallow, you should see the candy begin to toast! No fire required—just the power of the sun! Online resources Marshmallow melting web pages! worldwatts.com/marshmallows/solar_roaster.html www.altenergyhobbystore.com/marshmallow% 20roaster.htm bellnetweb.brc.tamus.edu/res_grid/cuecee05.htm 48 P r o j e c t 9 : B u i l d a S o l a r M a r s h m a l l o w M e l t e r Figure 6-4 Solar motor circuit. Project 9: Build a Solar Marshmallow Melter You will need ● Eggs! ● Drop of oil ● Hot sunny day Tools ● Black tarmac driveway ● Frying pan Sometimes, on a hot sunny day, the black tarmac 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 ability to act as a thermal mass and store heat. If you were to stand on say a flimsy piece of black card that had been left in the sun, it would feel warm to the touch; however, you would find that 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 Alaska! But if your climate permits, this is a nice trick! If there is not as much sun as you would like, try using reflectors to aim more solar energy onto your pan! In fact, with simple solar cooking, I have even heard of people baking cookies in their car by simply putting a black baking tray with cookie dough on their dashboard, and parking the car in a sunny setting with the windows up. They then return to the car at lunch to find a tray of cookies and a “bakery fresh” smelling car. It sure beats a Magic Tree for in-car air freshening! Online resources The following link is a great solar cooker site written specifically for younger kids. pbskids.org/zoom/activities/sci/solarcookers.html 49 P r o j e c t 1 0 : C o o k E g g s o n Y o u r D r i v e w a y Project 10: Cook Eggs on Your Driveway Using the Sun Figure 6-5 Solar egg frying. You will need ● Sheet of thin MDF ● Sheet of flexible mirror plastic ● Sheet of thin polystyrene ● Veneer panel pins Tools ● Bandsaw ● Pin hammer ● Sharp knife/scalpel ● Angle marking gauge This solar cooker is a very simple project to construct—we will be harnessing the sun’s energy from a relatively wide area and concentrating it to a smaller area using mirrors (read more in Chapter 8 about this). The area which we will concentrate it into will be lined with polystyrene to keep in the heat. Construct a box for your cooker out of MDF. I find small veneer pins to be very useful as they can be hammered neatly into the end grain of thin MDF without splitting the wood. For this application they are perfectly strong enough. When you have finished the box it should look something like Figure 6-6. Now you need to line the box with polystyrene, this will prevent the heat from escaping. The lined box will look like Figure 6-7. Now measure the size of the cube inside the lined polystyrene box. You should cut the mirror plastic to this size, and further line the box with it. Duck Tape is more than ideal for making good all of the joints and securing things into place. We now need to cut the mirrored reflectors. Cut a strip of mirror plastic about two feet wide on the bandsaw. Now, using an angle marking gauge, mark from the long side of the mirror to the very corner of the mirror, a line which makes an angle 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 50 P r o j e c t 1 1 : B u i l d a S o l a r C o o k e r Project 11: Build a Solar Cooker Figure 6-6 The box constructed from MDF. Figure 6-7 The box lined with polystyrene. Solar cooking recipes Potatoes For a start, cooking potatoes with a solar cooker dif- fers a bit from cooking them in a campfire, which you are probably used to, because if you wrap them in shiny reflective tin foil, the solar energy which you have gone to painstaking ends to concentrate onto the potato will simply be reflected! Brewing tea If you want to brew tea in a solar cooker, you can’t expect to get boiling water and then make your tea conventionally—instead take a jar and a couple of tea bags, put the tea bags in the jar along with some clean water (which you might have even got from your solar distilling apparatus!). Soups Soups are really easy to cook in a solar cooker. Furthermore, they are particularly forgiving if the amount of sunlight is suboptimal, as warmish vegetable soup is quite acceptable whereas rawish not fully cooked chicken is totally unacceptable! Nachos Everyone loves Nachos! So why not take a bag, 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! Bread Take some old baked bean tins and paint them black—you now have the perfect can for cooking bread! To cook some simple French bread you will need a packet of baker’s yeast, a tablespoon of sugar and a tablespoon of salt, five cups of white flour and a couple of cups of water. Baked potatoes This is a really nice cartoon about cooking potatoes in the sun. www.hunkinsexperiments.com/pages/potatoes.htm Online resources—cont’d Parvarti Solar Cooker www.angelfire.com/80s/shobhapardeshi/ twelvesided.html Windshield Shade Solar Cooker solarcooking.org/windshield-cooker.htm A solar cooker made from an old car windscreen reflector shade Double Angle Twelve Sided Cooker solarcooking.org/DATS.htm A simple cooker design from cardboard and tin foil Parabolic Solar Cooker www.sunspot.org.uk/Prototypes.htm A solar cooker with an aluminum reflector and card base Solar Bottle Pasteurizer solarcooking.org/soda-bottle-pasteurizer.htm A pasteurizing device powered by the sun, and made from recycled materials Solar Water Pasteurizer solarcooking.org/spasteur.htm Solar Chimney Dehydrator www.littlecolorado.org/solar.htm Simple plans to build a food drying device powered by the sun Solar Cooking in the Peruvian Andes www.sunspot.org.uk/Solar.htm Solar cooking in the developing world 53 S o l a r C o o k i n g R e c i p e s Dissolve the yeast in one cup of slightly warm water. Sift all of the dry matter into a clean bowl, stir in the yeast—water mix, add the water from the second cup in small amounts until the dough is sticky. Grease a baked bean can which has been painted black, being careful of any sharp edges, add the bread mixture and leave it in your solar oven. Solar cooking tips In many campsites and caravan parks, open fires are banned because of the mess they produce and the smoke which can be unpleasant for other visitors—so while everyone else has run out of gas in their cylinder, or is eating cold raw food, now would be a great time to crack open the solar cooker and make the rest of the campsite jealous! You really want to cook on days when the sky is clear and the sun can easily be seen—on a cloudy day, cooking will be painfully slow. One of the great things about solar cooking is that you can prepare everything in advance, leave it in your solar cooker, and when you return every- thing is cooked ready to eat—whereas your accomplices cooking with traditional methods still have to muck about and cook their food! Also—think like this—if you are cooking using conventional energy inside a home that is air conditioned, for every kWh of energy you input to your cooker, your air conditioning will use about another three trying to remove that heat from your home! 54 S o l a r C o o k i n g T i p s Solar Stills Chapter 7 Water—a precious resource The former World Bank Vice President Ismail Serageldin, said that “the next world war will be over water.” At first look, this statement seems almost non- sensical, we are surrounded by water, it falls from the skies and runs through our streams and rivers; however, not all of the world enjoys such plenti- ful access to water as we do in the developed world. In much of the developing world the land is arid, and clean drinking water can often mean a walk for tens of miles. This problem is exacerbated by heavy industry building factories which extract what little water there is. Our water is constantly recycled by the natural environment, it follows a pattern called the hydro- logical cycle, which can be very simply repre- sented by Figure 7-1. 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. A solar still effectively creates the hydrological cycle in miniature in an enclosed volume. The idea is that by evaporating water, all of the bacteria, salts and other contaminants are left behind, with the precipitate being pure, drinkable water. Even seawater can be desalinated using this process. There are a number of advantages to solar distillation: ● Free energy ● No prime movers required History of the solar still Solar stills are an old, tried and tested technology— the earliest record of a solar still being used is in 1551, when Arab alchemists used one to purify water. Mouchot, whose name also springs up a couple of other times in this book also worked with solar distillation around 1869. 55 Figure 7-1 The hydrological cycle. Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use. You will need: ● Plywood/oriented strand board ● Framing ● Screws ● Glazing (glass/polycarbonate) ● Metal U-strip ● Black silicone ● Low-profile guttering ● Low-profile guttering end pieces ● Tube ● Two stop cock valves 58 P r o j e c t 1 5 : B u i l d a S o l a r B a s i n S t i l l 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 Tools ● Jigsaw ● Screwdriver ● Squeegee This project is scaleable depending on your require- ments for water, which is why no specific mea- surements are presented. First of all, you will need to calculate your water needs. Solar stills can generally produce around a gallon of water per 8 square feet, this is around four liters per square meter. This assumes that your collector receives 5 hours of good sunlight per day. Obviously the performance of your still will be highly variable, depending on the amount of sun your collector receives. You need to construct a wooden box from ply- wood or oriented strand board, with gently sloping sides. This is well within the capability of someone with even modest carpentry skills. At a position near the tallest side of the box you will need to drill a hole and insert a pipe with a valve that can be opened and shut, to allow you to introduce brackish water to be purified. Then, take a squeegee and some black silicone. You need to spread this mixture on the bottom face of the wooden box so that it gets a thin uniform coat. Less important are the sides, but you should ensure that by the time you are finished, the inside of the box is fully lined with silicone. At the front of the still, that is to say on the shortest side of the box, you need to make a small gutter. This gutter will serve to collect your puri- fied water which will run down by the force of gravity from your glazing. You need to make this gutter out of a waterproof material. The low-profile guttering sold for sheds and outbuildings is ideal. A hole needs to be drilled in the side of the frame of your still, and a pipe introduced to allow you to siphon off the clean water. The silicone has two functions. First of all, it acts as a black collector surface, absorbing radiation and creating heat. But secondly, it pro- tects your wood by making the enclosure water- proof. On top of this sealed box you need to put a sheet of glazing. This needs to be sealed around the edges with frame sealant to ensure a good water- tight fit. The brackish water should never be allowed to rise above the level of the guttering, as it would contaminate the clean water. The whole solar still is illustrated diagrammatically in Figure 7-6. 59 P r o j e c t 1 5 : B u i l d a S o l a r B a s i n S t i l l Figure 7-6 Diagram of the basin type still. This page intentionally left blank 63 S o l a r C o l l e c t o r s 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. You will need: ● Sheet of MDF ● Sheet of flexible mirror acrylic ● 72 long self-tapping screws Optional ● Silicone sealant Tools ● Drill bit ● Hand/cordless drill ● Glue gun and sticks ● Ruler ● Set square ● Bandsaw Optional ● Mastic gun OK, so you have finally decided—the time is nigh to melt your little brother. While he might be hard to melt, you can certainly singe him with this mod- ular solar death ray! Don’t worry—you won’t need lots of chairs and big A4 mirrors like the guys at MIT! Instead, this modular death ray relies on little tiles which are cut from plastic mirror. The plan is really simple—you build the death ray a tile at a time. One tile is good to experiment Warning I have used acrylic mirror in this project because it is very easy to work with, and can be cut easily using a band saw; however, there is nothing to stop you using a glass mirror if it is available and you have the correct tools to cut it and work with it—my only advice is it will be harder to work with and much more fragile. 64 P r o j e c t 1 6 : B u i l d Y o u r O w n “ S o l a r D e a t h R a y ” Figure 8-5 Working it all out! Image courtesy Massachusetts Institute of Technology. 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, please note that the screw does not need to be a tight fit in the hole, as it would be if you were joining two pieces of wood. Instead, the screw is only going to be used for light adjustment, so the screw can be a relatively slack fit in the hole. Looking at your board of squares, you are going to be drilling two holes in each 6 cm square. The holes will be at the top left and bottom right, where the lines cross to form the smaller square inside each square. Sounds confusing, well, take a look at the furnace drilling diagram (Figure 8-7), which shows where to drill in each square. Once you have drilled all 72 holes, you are going to need to think about getting those screws in place. This is a really tedious job, so either ask a younger sibling, or failing that, if you are an only child you might like to consider investing in an electric screwdriver—the lazy man’s way out. You want to put the screws in so that they just protrude from the other side a little way (Figure 8-8). Now is a good time to take your acrylic sheet of mirror, and, on a bandsaw, cut 36 identical 65 P r o j e c t 1 6 : B u i l d Y o u r O w n “ S o l a r D e a t h R a y ” Figure 8-6 Sheet of MDF marked out. Figure 8-7 Furnace drilling diagram. Figure 8-8 Solar furnace with the screws in place. 68 P a r a b o l i c D i s h C o n c e n t r a t o r s 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. You will need ● Old satellite dish ● Bathroom/kitchen tile adhesive ● Small mirror tiles Tools ● Adhesive comb ● Spreader This is an incredibly easy way to make a parabolic dish concentrator, and even better, it recycles old stuff! Take a satellite dish, and dunk your adhesive comb into the bathroom/kitchen tile adhesive. Working from the center of the dish outwards, spread the adhesive using the “comb” side of the spreader. What the comb does is apply the adhesive in a ridged manner, this means that when you press the tiles into the adhesive, they have room to settle and even themselves out. If you just apply straight flat 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 line with the plane of the parabolic satellite dish. Caution I strongly recommend that you perform this operation in your garage or in a shaded area, as with the addi- tion of more mirrors and a little sunlight, a focal point can quickly develop which has the potential to burn you while you are working! Note You need to purchase some tile adhesive—the sort of stuff you would use when applying ceramic tiles onto your walls at home. You will need to choose a tile adhesive which is waterproof, as a non-waterproof tile adhesive will not stand outside use—for this purpose kitchen/bathroom adhesive is strongly recom- mended. 69 P r o j e c t 1 7 : B u i l d Y o u r O w n P a r a b o l i c C o n c e n t r a t o r Figure 8-14 University of Oxford solar energy kit. Project 17: Build Your Own Parabolic Dish Concentrator Free energy? Solar dish collectors take the immense power of the sun, over the area of a dish, and concentrate that energy by means of reflectors to a central point. At the end of 2004, Sandia National Laboratory announced that they were working with Stirling Energy Systems to build and test a six-dish array. These six dishes would be capable of producing 150 kW of power during the day, enough to power 40 homes. Each dish comprises 82 individual mirrors all focused to a single central point (Figure 8-15). This causes a massive amount of heat to be generated at that point which is used to drive a Stirling engine. The Stirling engine produces mechanical movement, which is converted to electrical energy by a conven- tional generator arrangement (Figure 8-16). One of the problems inherent with solar dish systems is that they must track the sun—older systems used really heavy mirrors which meant that the motors required to track the sun had to be big and beefy and drew a lot of energy. With this new array of collectors, the mirrors have been designed with a honeycomb structure so they are strong, and yet very light indeed. This is said to be the largest array of solar dishes in the world, but big plans are afoot. Eventually, when the technology is fully proven, massive arrays of 20,000 units are imagined filling vast fields and plains—producing free energy from the sun (Figure 8-17). Note If you are messy and get adhesive everywhere, you want to wait a little while until the tiles are firmly in place, but not so long as for the adhesive to dry, as it will only be harder to get off once it has set. To remove adhesive while it is still wet, you need a moist cloth, which you can wipe over the surface of your mirror tiles, taking off any excess adhesive with the cloth. 70 P r o j e c t 1 7 : B u i l d Y o u r O w n P a r a b o l i c C o n c e n t r a t o r Figure 8-15 Solar dish engine system under test. Image courtesy Sandia National Laboratories/Randy Montoya 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 up a few results for optical suppliers. There are a lot of vendors selling kits to make large-screen projector TVs from an old screen—these lenses are often very overpriced. Online auction sites are another good source, or school science catalogs. There are also a couple of entries in the Supplier’s Index (see Appendix) for new Fresnel lenses. How does a Fresnel lens work? To understand how a Fresnel lens is constructed and works, we are going to need to do a little thought experiment. Picture this. You have a glass lens which is flat on one side, and round on the 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 to be lighter, they do not possess the same optical clarity as ordinary lenses—which is why they are not used in cameras or microscopes. Take a look at Figure 8-20. It demonstrates that although our Fresnel lens is only a thin sheet of plastic, it can magnify things significantly. Now try and use your Fresnel lens as a solar concentrator, hold it above a piece of paper until you form a bright white dot of sunlight (Figure 8-21). Notice how much brighter the concentrated dot is compared with the rest of the paper, which is simply illuminated by the sun. 73 P r o j e c t 1 8 : E x p e r i m e n t w i t h F r e s n e l C o n c e n t r a t o r s Figure 8-19 Diagram showing how a Fresnel lens compares to a conventional lens. Figure 8-20 A thin Fresnel lens shown magnifying. A few experiments that you can do with a Fresnel solar concentrator Use a thermometer to measure the temperature of the point where the sun’s energy is concentrated— see what difference it makes if the bulb is covered in tin foil or black paper. The intensity of the concentrated light might be enough to singe a feather, or even a thin shaving of rubber from a balloon or latex glove. Try shining the beam of light onto a photovoltaic cell connected to a multimeter and load—see how it affects the amount of power produced. You might also want to see if you can melt a wax candle using the power of your concentrated light. 74 P r o j e c t 1 8 : E x p e r i m e n t w i t h F r e s n e l C o n c e n t r a t o r s Figure 8-21 Concentrating solar energy using a Fresnel lens. Pumping water is an essential task—we need water to drink, wash, cook, and sanitize and irrigate with. Water can be used for utility, or it can be used for dramatic effect, creating tranquility and pleasant- ness in our surroundings. Using solar energy to pump water makes quite a bit of sense. Our demand for water often rises when the sun is shining. Think of agriculture— there is more sun in the summer, and that is when we want pumped water to irrigate our crops. We can use water features to enhance our envi- 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 the cycle repeats again. This is shown in the display at the Centre for Alternative Technology, U.K. (Figure 9-2). This has some interesting consequences for our energy supply. The pumped power station at Dinorwig, Wales, draws water up into a large reservoir using excess power from the grid. When there is a shortage of power, that water is allowed to flow down hill through hydroelectric generators, producing power as it does so. As we can see, there are many cogent reasons for using solar energy to pump our water—now let’s move on to some practical projects: 75 Chapter 9 Solar Pumping Figure 9-1 Photovoltaic-powered fountains enhance the CEME, U.K. Copyright © 2007 by The McGraw-Hill Companies, Inc. Click here for terms of use. 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. Figure 9-5 Diagram of the solar water feature. 78 P r o j e c t 1 9 : B u i l d a S o l a r - P o w e r e d F o u n t a i n One you have satisfied yourself that your pump and module work together satisfactorily, you will need to install your feature. Things to consider Flexible plastic tubing and jubilee clips are infinitely easier to work with than copper pipe and solder. You will want to provide some sort of mechanical protection for your cable to ensure that it does not become chafed, or cannot easily be damaged by gardening activities such as digging. Encase the pipe in a hard plastic pipe, or mount it above ground where it can clearly be seen. Hint Because of the low-voltage, low-current nature of a single photovoltaic module connected to a pump, many region’s electrical codes will not require a fuse, breaker, or other disconnection device; however, check your local regulations to be on the safe side. 79 P r o j e c t 1 9 : B u i l d a S o l a r - P o w e r e d F o u n t a i n This page intentionally left blank between these and crystalline cells is that rather than using crystalline silicon, these use chemical compounds to semiconduct. The chemical com- pounds are deposited on top of a “substrate,” that is to say a base for the solar cell. There are some formulations that do not require silicon at all, such as CIS (copper indium diselenide) and cadmium telluride. However, there is also a process called “amorphous silicon,” where silicon is deposited on a substrate, although not in a uniform crystal structure, but as a thin film. In addition, rather than being slow to produce, thin-film solar cells can be produced using a continuous process, which makes them much cheaper. However, the disadvantage is that while they are cheaper, thin-film solar cells are less efficient than their crystalline counterparts. Some different solar photovoltaic technologies are compared in Table 10-1. Figures are given for the efficiency of the cell technology, and the average area of cells required to generate 1 kW peak power when facing 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. However, the problem with them is that they are expensive to produce and quite inflexible (as you are limited to constructing panels from standard cell sizes and cannot change or vary their shape). By contrast, thin-film cells are cheap to produce, and the only factor limiting their shape is the substrate they are mounted on. This means that you can create large cells, and cells of different shapes and sizes, all of which can be useful in certain applications. We are now going to take a detailed look at making two different types of solar cell, one will be a crystalline solar cell, and the other a thin-film solar cell. Both of the experiments are designed to be “illustrative,” rather than to actually make a cell with a useful efficiency. The technology required to make silicon solar cells is out of the reach of the home experimenter, so we are going to “illustrate” the process of how a solar cell is made, using things you can find in your kitchen. For thin-film solar cells, we are going to make an actual solar cell, which responds to light with changing electrical properties; however, the efficiency of our cell will be very poor, and it will not be able to generate a useful amount of electricity. How are crystalline photovoltaic cells made? In this section we are going to look at how photo- 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 kitchen experiments that mimic the process that happens in solar cell factories all around the world. How do they work? First of all, let’s cover a little bit of the theory. Ordinary silicon forms into a regular crystalline structure. If you look at Figure 10-3, you can see the way that the silicon atoms align themselves into a regular array. To make silicon “semiconducting,” we can take a little bit of another chemical, in this case boron, and 83 S o l a r P h o t o v o l t a i c s Table 10-1 Efficiency of different cell types Area required to generate 1 kW peak Cell material Efficiency power Monocrystalline silicon 15–18% 7–9 m2 Polycrystalline silicon 13–16% 8–11 m2 Thin-film copper indium 7.5–9.5% 11–13 m2 diselenide (CIS) Cadmium telluride 6–9% 14–18 m2 Amorphous silicon 5–8% 16–20 m2 Source data: Deutsche Gesellschaft fur Sonnenenergie e.V. introduce it to the silicon. Where there is a boron atom, there is also a missing electron. This creates a “hole” in the outer shell of the boron atoms and its neighboring silicon atom (Figure 10-4). If we add a little bit of phosphorus to our silicon, we get the opposite effect, a “spare” electron (Figure 10-5), which doesn’t quite know where to 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.” A photovoltaic solar cell is a bit like a sandwich. It is made from layers of different types of silicon, as illustrated in Figure 10-6. Starting from the base, we have a large contact. Then on top of this we have a layer of p-type silicon, a junction called the space charge region 84 S o l a r P h o t o v o l t a i c s Figure 10-3 Plain old silicon—its atomic structure. Figure 10-4 Silicon doped with boron—note the missing electron. Figure 10-5 Silicon doped with phosphorus—note the spare electron. Figure 10-6 Cutaway solar cell. where the magic occurs, and a slice of n-type silicon on top. On top of all this is layered a grid electrode, which does the job of making the other contact. Now, photons from the sun hit our solar cell, and in doing so “spare” negatively charged electrons, are “knocked” across the boundary between p- and n-silicon, which causes a flow of electrons around the circuit. We are now going to look at how the silicon for these solar cells is manufactured, using some things you can do at home. You will need ● Plastic coffee jar (empty) ● Skewer ● Hardboiled egg ● Sugar ● Food coloring Tools ● Compass ● Egg slicer To make a photovoltaic cell we need silicon, this project is going to show you how solar cells are produced from crystalline silicon. The words “crystalline silicon” should indicate to you that this type of solar cell is made from crystals of silicon. We saw earlier how silicon aligns itself into a regular crystalline array, now we are going to look at growing this crystal. In industry, silicon crystals are grown to form a uniform cylinder of silicon which is used as the base material for crystalline solar cells. There is plenty of silicon about on the earth, in fact, as mentioned previously, after oxygen it is the second most abundant element. When you think that sand and quartz all contain silicon and then imagine the amount of sand in the world, you begin to realize that we are not going to run out of silicon in a hurry! The problem with sand is that it also contains oxygen in the form of silicon dioxide, which must be removed. The industrial process used to produce silicon requires temperatures of around 3270∞F (which is about 1800∞C). Obviously we can’t experiment with these sorts of temperatures at home—but we can recreate the process! If you don’t want to get the individual bits and bobs, a couple of educational scientific vendors sell rock-growing kits. These links are to suppliers of kits of parts: ● scientificsonline.com/product.asp?pn=3039234& bhcd2=1151614245 ● www.sciencekit.com/category.asp_Q_c_E_737919 ● www.scienceartandmore.com/browseproducts/ Rock-Candy-Growing-Experiment-kit.html If you want to do it all yourself, then you can see from Figure 10-7 that the process is a relatively easy one! You are going to need a saturated sugar solution, this will sit in the lid of your coffee jar. Now, take a large crystal of sugar, often sold as “rock sugar” and “glue” it to the end of the skewer. Next, drill a hole the same diameter as the skewer, and poke the skewer through the bottom of the coffee jar. Stand it on a windowsill and lower the crystal into the saturated sugar solution. Over some Project 20: Grow Your Own “Silicon” Crystals 85 P r o j e c t 2 0 : G r o w Y o u r O w n “ S i l i c o n ” C r y s t a l s