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Solar livingsourcebook excerpt

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This is an overview of Solar Energy.

This is an overview of Solar Energy.

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    Solar livingsourcebook excerpt Solar livingsourcebook excerpt Document Transcript

    • SPECIAL 30 Anniversary th th Edition Your complete guide to renewable energy technologies and sustainable living JOHN SCHAEFFER
    • Chapter 3 Sunshine to Electricity Renewable Energy 101—Solar, Wind, and Hydroelectric Bet ter than 99% of the world ’ s e n e rg y comes from the Sun. Some is har- vested directly by plants, trees, and solar panels; much is used indirectly in the form of wood, coal, or oil; and a tiny bit is supplied by the nonsolar sources, geothermal and nuclear power. Solar panels receive this energy directly. Both wind and hydro power sources use solar energy indirectly. The coal and petroleum resources that we’re so busy burning up now represent stored solar energy from the distant past, yet every single day, enough free sunlight energy Every single day, falls on Earth to supply our energy needs for four to five years at our present rate of con- enough free sunlight sumption. Best of all, with this energy source, there are no hidden costs and no borrowing or dumping on our children’s future. The amount of solar energy we take today in no way energy falls on Earth to diminishes or reduces the amount we can take tomorrow or at any time in the future. supply our energy needs Solar energy can be directly harnessed in a variety of ways. One of the oldest uses of for four to five years solar is heating domestic water for showering, dishwashing, or space heating. At the turn of at our present rate of the century, solar hot-water panels were an integral part of 80% of homes in southern Cali- fornia and Florida until gas companies, sensing a serious low-cost threat to their businesses, consumption. started offering free water heaters and installation. (See pages 388-401 for the full story of solar hot-water heating.) What we’re going to cover in this chapter is one of the more recent, cleanest, and most direct ways to harvest the Sun’s energy: photovoltaics, or PV. What Are Photovoltaic Cells? Photovoltaic cells were developed at Bell Labo- map on page 103 for details.) As the true envi- ratories in the early 1950s as a spinoff of transis- ronmental and societal costs of coal and petro- tor technology. Very thin layers of pure silicon leum become more apparent, PVs promise to be are impregnated with tiny amounts of other a major power resource in the future. And with elements. When exposed to sunlight, small worldwide petroleum sources close to peak, we amounts of electricity are produced. They were are rapidly running out of “cheap” oil, making mainly a laboratory curiosity until the advent of renewable energy all the more critical. Who spaceflight in the 1950s, when they were found says that space programs have no benefits for to be an efficient and long-lived, although stag- society at large? geringly expensive, power source for satellites. in 1954, bell Also, the utility companies couldn’t figure out Telephone systems how to get their wires out into space, so PV was announced the invention of the really the only option! Since the early ’60s, PV bell solar battery, cells have slowly but steadily come down from a “forward step in prices of over $40,000 per watt to current retail putting the energy of prices of around $5 per watt, or in some cases the sun to practical as low as $3 per watt for distributors or in very use.” large quantities. Using the technology available today, we could equal the entire electric pro- duction of the United States with photovoltaic power plants using about 10,000 square miles, or less than 12% of the state of Nevada. (See the solar living sourcebook 93
    • Fifty Years of Photovoltaics SunShine to electricity Solar Energy Still Strikes a Powerful Chord Hearing the hit songs of Rosemary Clooney or Perry Como was an ordinary occurrence in the mid-1950s. But it turned extraor- dinary on Sunday, April 25, 1954. That was the day that Bell Laborato- ries executives electrified members of the press with music broadcast from a chemist calvin Fuller gets ready to diffuse boron into transistor radio—powered by the first negative silicon. The addition of boron resulted in the silicon solar cell. Bell called its invention first solar cell capable of producing useful amounts of electricity from the sun. “the first successful device to convert useful amounts of the Sun’s energy di- rectly and efficiently into electricity.” computers and cell telephony—that is, for ev- The discovery was, indeed, music to ery doubling of production, the price drops by people’s ears. The New York Times her- 15%-20%. At this rate, PV should be competi- alded it as “the beginning of a new era, tive with fossil fuel-generated power company leading eventually to the realization electricity with no rebates or incentives whatso- of one of mankind’s most cherished ever within the next few years. dreams—the harnessing of the almost limitless energy of the Sun for the uses of civilization.” Where Will Solar Energy Be After Its First 100 Years— Single Cell Gives Birth in 2054? to Millions Of course, the satisfaction of using a renewable This 50-year-old prophecy has, in many energy source may be the biggest motivator of ways, come to fruition, with a billion all—and that’s what fuels our excitement most. watts of solar-electric modules now pow- As Margaret Mead said so eloquently, “Never ering satellites, telescopes, homes, water doubt that a small group of thoughtful, com- pumps, and even Antarctic research sta- mitted citizens can change the world. Indeed, it tions. is the only thing that ever has.” Today’s solar cells are a vast improve- Real Goods has now solarized more than ment on their ancestors—achieving 60,000 homes and businesses, and we can’t wait 16%-19% efficiency compared with the to see what will happen as that number gets big- 6% efficiency of Bell Labs’ foray into ger over the next 50 years. You can count on the solar industry. Silicon is still used— Real Goods to continue leading the way. though in slightly different forms—to achieve higher efficiency rates as well as lower costs. Lab tests using single-crys- A Brief Technical Explanation tal silicon modules, for example, have A single PV cell is a thin semiconductor sand- produced efficiency rates of up to 24%. wich, with a layer of highly purified silicon. The two- to threefold increase in efficiency is The silicon has been slightly doped with boron only part of the equation in the success of pho- on one side and phosphorus on the other side. tovoltaics—an industry that has grown more Doping produces either a surplus or a deficit of than 20% compounded per year since 1980 and electrons, depending on which side we’re look- 50% per year recently. A thousandfold price ing at. Electronics-savvy folks will recognize drop since 1954, along with tax incentives and these as P- and N-layers, the same as transis- rebates, have made the move to solar power tors use. When our sandwich is bombarded by economically feasible for many homeowners sunlight, photons knock off some of the excess and businesses, with typical payback periods of electrons. This creates a voltage difference be- less than 10 years. PV seems to follow the same tween the two sides of the wafer, as the excess economic rules as other new technologies, like electrons try to migrate to the deficit side. In 94 gaiam real goods
    • silicon, this voltage difference is just under half cal limits, however, to size, efficiency, and how a volt. Metallic contacts are made to both sides much sunlight a cell can tolerate. of the wafer. If an external circuit is attached to Since 0.5-volt solar panels won’t often do us SunShine to electricity the contacts, the electrons find it easier to take much good, we usually assemble a number of the long way around through our metallic con- PV cells for higher voltage output. A PV “mod- ductors than to struggle through the thin silicon ule” consists of many cells wired in series to layer. We have a complete circuit and a current produce a higher voltage. Modules consisting of flows. The PV cell acts like an electron pump. about 36 cells in series have become the indus- There is no storage capacity in a PV cell; it’s try standard for large power production. This simply an electron pump. Each cell makes just makes a module that delivers power at 17 to 18 under half a volt regardless of size. The amount volts, a handy level for 12-volt battery charg- of current is determined by the number of elec- ing. In recent years, as PV modules and systems trons that the solar photons knock off. We can have grown larger, 24-volt modules consisting get more electrons by using bigger cells, or by of 72 cells have also become standardized. The using more efficient cells, or by exposing our module is encapsulated with tempered glass cells to more intense sunlight. There are practi- (or some other transparent material) on the A Technical Step Back in Time B efore the invention of the silicon solar cell, scien- tists were skeptical about the success of solar as a renewable energy source. Bell Labs’ Daryl Chapin, assigned to research wind, thermoelectric, and solar energy, found that existing selenium solar cells could not generate enough power. They were able to muster only 5 watts per square meter—converting less than 0.5% of incoming sunlight into electricity. the Solar Cell that almost Never Was Chapin’s investigation may have ended there if not for colleagues Calvin Fuller and Gerald Pearson, who discovered a way to transform silicon into a superior conductor of electricity. Chapin was encouraged to find that the silicon solar cell was five times more efficient than selenium. He theorized that an ideal silicon solar The three inventors of the first silicon solar cell, gerald Pearson, daryl cell could convert 23% of incoming solar energy into chapin, and calvin Fuller, examine their cells at their bell lab. electricity. But he set his sights on an amount that would rank solar energy as a primary power source: 6% permanently fix the P-N junction at the top of the cell. efficiency. When Fuller added arsenic to the silicon and coated it with an ultrathin layer of boron, it allowed the team to Nuclear Cell trumps Solar Scientists make the electrical contacts they had hoped for. Cells While Chapin, Pearson, and Fuller faced chal- were built using this mixture until one performed at the lenges in increasing the efficiency of the silicon cell, benchmark efficiency of 6%. archrival RCA Laboratories announced its invention of the atomic battery—a nuclear-powered silicon cell. Solar Bursts the atomic Bubble Running on photons emitted from Strontium-90, the After releasing the invention to the public on April battery was touted as having the potential to run hear- 25, 1954, one journalist noted, “Linked together electri- ing aids and wristwatches for a lifetime. cally, the Bell solar cells deliver power from the Sun at That turned up the heat for Bell’s solar scientists, the rate of 50 watts per square yard, while the atomic who were making strides of their own by identifying cell recently announced by the RCA Corporation the ideal location for the P-N junction—the foundation merely delivers a millionth of a watt” over the same of any semiconductor. The Bell trio found that shifting area. The solar revolution was born. the junction to the surface of the cell enhanced conduc- Special thanks to John Perlin, author of From Space to tivity, so they experimented with substances that could Earth: The Story of Solar Electricity. solar living sourcebook 95
    • our current energy practices are borrowing from our children. Worldwide, there are cur- rently over 1 million homes that derive their SunShine to electricity primary power from PV. Because they don’t rely on miles of exposed wires, residential PV sys- tems are more reliable than utilities, particularly when the weather gets nasty. PV modules have no moving parts; degrade very, very slowly; and boast a lifespan that isn’t fully known yet but will be measured in multiple decades. Standard factory PV warranties are 25 years. Compare this with any other power generation technol- ogy or consumer goods. Could you find a car or truck or computer with a 25-year warranty? If you could, you’d probably buy it! Construction Types There are currently four commercial produc- tion technologies for PV cells. front surface and with a protective and water- proof material on the back surface. The edges SiNgle CryStalliNe are sealed for weatherproofing, and there is This is the oldest and most expensive produc- often an aluminum frame holding everything tion technique, but it’s also the most efficient together in a mountable unit. A junction box, sunlight conversion technology commercially or wire leads, providing electrical connections available. Complete modules have sunlight-to- is usually found on the module’s back. Truly wire output efficiency averages of about 10%- weatherproof encapsulation was a problem with 12%. Efficiencies up to 22% have been achieved the early modules assembled 20 years ago. We in the lab, but these are single cells using highly have not seen any encapsulation problems with exotic components that cannot economically be glass-faced modules in many years. used in commercial production. Many applications need more than a single Boules (large cylindrical cylinders) of pure PV module, so we build an “array.” A PV array single-crystal silicon are grown in an oven, consists of a number of individual PV modules then sliced into wafers, doped, and assembled. that have been wired together in series and/or This is the same process used in manufacturing parallel to deliver the voltage and amperage a transistors and integrated circuits, so it is well- sharp 123 Pv module particular system requires. An array can be developed, efficient, and clean. Degradation is as small as a single pair of modules, or large very slow with this technology, typically 0.25%- enough to cover acres. 0.5% per year. Silicon crystals are characteristi- PV costs are down to a level that makes them cally blue, and single crystalline cells look like the clear choice for remote and grid-intertie deep blue glass. Examples are Sunpower, Solar power applications. They are routinely used World, and Sharp single-crystalline products. for roadside emergency phones and most tem- porary construction signs, where the cost and polyCryStalliNe or MultiCryStalliNe trouble of bringing in utility power outweighs In this technique, pure, molten silicon is cast the higher initial expense of PV, and where into cylinders, then sliced into wafers off the mobile generator sets present more fueling and large block of multicrystalline silicon. Poly- maintenance trouble. It’s hard to find new gate crystal is slightly lower in conversion efficiency opener hardware that isn’t solar powered. Solar compared with single crystal, but the manufac- with battery backup has proven to be a far more turing process is less exacting, so costs are a bit reliable power source, and it’s usually easier to lower. Module efficiency averages about 10%- obtain at the gate site. More than 150,000 homes 11%, sunlight to wire. Degradation is very slow in the United States, largely in rural sites, de- and gradual, similar to that of single crystal, dis- pend on PVs as a primary power source, and cussed above. Crystals measure approximately this figure is growing rapidly as people begin 1 centimeter (two-fifths of an inch), and the to understand how clean, reliable, and mainte- multicrystal patterns can be clearly seen in the nance-free this power source is, and how deeply cell’s deep blue surface. Doping and assembly 96 gaiam real goods
    • are the same as for single-crystal modules. Ex- amples are Sharp, Sanyo, and Kyocera polycrys- talline products. SunShine to electricity single crystalline module StriNg riBBoN This clever technique is a refinement of polycrys- talline production. A pair of strings are drawn up through molten silicon, pulling up between them a thin film of silicon like a soap bubble. It cools and crystallizes, and you’ve got ready- to-dope wafers. The ribbon width and thickness can be controlled, so there’s far less slicing, dic- multicrystalline ing, or waste, and production costs are lower. module Sunlight-to-wire conversion efficiency is about 8%-9%. Degradation is the same as for ordinary slice-and-dice polycrystal. Examples are Ever- green modules. aMorphouS or thiN FilM In this technique, silicon material is vapor- ized and deposited on glass or stainless steel. This production technology costs less than any string ribbon module other method, but the cells are less efficient, so more surface area is required. Early production methods in the 1980s produced a product that faded up to 50% in output over the first three to five years. Present day thin-film technology has dramatically reduced power fading, although it’s still a long-term uncertainty. Uni-Solar has a “within 20% of rated power at 20 years” war- Thin film ranty, which relieves much nervousness, but we honestly don’t know how these cells will fare with time. Sunlight-to-wire efficiency averages about 5%-7%. These cells are often almost black in color. Unlike other modules, if glass is used on amorphous modules, it is not tempered, so breakage is more of a problem. Tempered glass can’t be used with this high-temperature depo- to work with. Under most circumstances, this sition process. If the deposition layer is stainless isn’t enough voltage to pass through your body. steel and a flexible glazing is used, the result- While not impossible, it’s pretty difficult to hurt ing modules will be somewhat flexible. These yourself on such low voltage. Still, whenever are often used as marine or RV modules. In the working with electricity, make sure you take mid ’90s, it appeared that amorphous modules the necessary safety precautions. Batteries how- could deliver the magic $2 per watt that would ever, where enormous quantities of accumulat- make solar sprout on every rooftop. There was a ed energy are stored, can be very dangerous if rush to build assembly plants. Oddly, it turned mishandled or miswired. Please see Chapter 4, out that few homeowners wanted to cover every which discusses batteries and safety equipment, square foot of their roof with an unproven and for more information. still fairly expensive solar product. We’re seeing Multiple modules can be wired in parallel fewer examples of thin-film technology. Uni- or series to achieve any desired output. As sys- Solar makes flexible, unbreakable modules. tems get bigger, we usually run collection and storage at higher DC voltages because trans- mission is easier. Small systems processing up Putting It All Together to about 2,000 watt-hours are fine at 12 volts. The PV industry has standardized on 12-, 24-, Systems processing 2,000-7,000 watt-hours will or 48-volts for battery systems. These are mod- function better at 24 volts, and systems running erately low voltages, which are relatively safe more than 7,000 watt-hours should probably be solar living sourcebook 97
    • PV modules do not convert 100% of the en- What’s a Watt? ergy that strikes them into electricity (we wish!). Current commercial technology averages about SunShine to electricity a Watt (W) is a standard metric measurement of electrical 10%-12% conversion efficiency for single- and power. It is a rate of doing work. multicrystalline modules, and 5%-7% for amor- a Watt-hour (Wh) is a unit of energy measuring the total phous modules. Conversion rates slightly over amount of work done during a period of time. (This is the 20% have been achieved in the laboratory by us- measurement that utility companies make to charge us for the ing experimental cells made with esoteric and electricity we consume.) rare elements. But these elements are far too expensive to ever see commercial production. an amp (a) is a unit measuring the amount of electrical cur- Conversion efficiency for commercial single- rent passing a point on a circuit. It is the rate of flow of elec- and multicrystalline modules is not expected trons through a conductor such as copper wire: 1 Amp = 6.28 to improve; this is a mature technology. There’s billion billion electrons moving past a point in one second. better hope for increased efficiency with amor- (Amps are analogous to the water-flow rate in a water pipe.) phous technology, and much research is cur- a Volt (V) is a unit measuring the potential difference in rently underway. electrical force, or pressure, between two points on a circuit. This force on the electrons in a wire causes the current to flow. (Volts are analogous to water pressure in a pipe.) How Long Do PV Modules In summary, a Watt measures power, or the rate of doing Last? work, and a Watt-hour measures energy, or the amount of PV modules last a long, long time. How long work done. Watts can be calculated if you know the voltage we honestly don’t yet know, as the oldest ter- and the amperage: Watts = Volts x Amps. More pressure or restrial modules are barely 45 years old and still more flow means more power. going strong. In decades-long tests, the fully developed technology of single- and polycrystal modules has shown to degrade at fairly steady running at 48 volts. These are guidelines, not rates of 0.25%-0.5% per year. First-generation hard and fast rules! The modular design of PV amorphous modules degraded faster, but there panels allows systems to grow and change as are so many new wrinkles and improvements system needs change. Modules from different in amorphous production that we can’t draw manufacturers, different wattages, and various any blanket generalizations for this module ages can be intermixed with no problems, so type. The best amorphous products now seem long as all modules have a rated voltage output to closely match the degradation of single-crys- within about 1.0 volt of each other. Buy what tal products, but there is little long-term data. you can afford now, then add to it in a few years Most full-size modules carry 25-year warran- Conversion efficiency when you can afford to expand. ties, reflecting their manufacturers’ faith in the for commercial single- and multicrystalline Efficiency modules is not expected By scientific definition, the Sun delivers 1,000 watts (1 kilowatt) per square meter at noon to improve; this is a on a clear day at sea level. This is defined as a mature technology. “full Sun” and is the benchmark by which mod- ules are rated and compared. That is certainly There’s better hope for a nice round figure, but it is not what most of increased efficiency us actually see. Dust, water vapor, air pollution, seasonal variations, altitude, and temperature with amorphous all affect how much solar energy your modules technology, and much actually receive. For instance, the 1991 erup- tion of Mt. Pinatubo in the Philippines reduced research is currently available sunlight worldwide by 10%-20% for a underway. couple of years. It is reasonable to assume that most sites will actually average about 85% of full Photovoltaic prices have decreased dramatically since Sun, unless they are over 7,000 feet in elevation, 1955. Prices continue to drop 10%-15% per year as demand in which case they’ll probably receive more than and production increase. We have seen prices as low as $3 100% of full Sun. per watt for very large systems in late 2007. 98 gaiam real goods
    • durability of these products. PV technology is the modules down. Do not hose them off when It’s almost laughable closely related to transistor technology. Based they’re hot, since uneven thermal shock could on our experience with transistors, which just theoretically break the glass. Wash them in how easy the SunShine to electricity fade away after 20 years of constant use, most the morning or evening. For PV maintenance, maintenance is for manufacturers have been confidently predict- that’s it. ing 20-year or longer life spans. However, keep PV modules. Because in mind that PV modules are seeing only six to they have no moving eight hours of active use per day, so we may find Control Systems that life spans of 60-80 years are normal. Cells Controls for PV systems are usually simple. parts, they are virtually that were put into the truly nasty environment When the battery reaches a full-charge voltage, maintenance free. of space in the late 1960s are still functioning the charging current can be turned off or direct- well. The bottom line? We’re going to measure ed elsewhere. Open-circuited PV module volt- Basically, you keep the life expectancy of PV modules in decades— age rises 5-10 volts and stabilizes harmlessly. It them clean. how many, we don’t yet know. does no harm to the modules to sit at open-cir- cuit voltages, but they aren’t doing any work for you either. When the battery voltage drops to a Payback Time for certain set-point, the charging circuit is closed and the modules go back to charging. With the Photovoltaic Manufacturing solid-state PWM (Pulse Width Modulated) Energy Investment controllers, this opening and closing of the cir- cuit happens so rapidly that you’ll simply see a In the early years of the PV industry, there was stable voltage. The most recent addition to PV a nasty rumor circulating that said PV mod- ules would never produce as much power over their lifetimes as it took to manufacture them. During the early years of development, when A Mercifully Brief Glossary of transistors were a novelty, and handmade PV modules costing as much as $40,000 per watt PV System Terminology were being used exclusively for spacecraft, this aC (alternating current)—This refers to the standard utility- was true. The truth now is that PV modules pay supplied power, which alternates its direction of flow 60 times back their manufacturing energy investment per second, and for normal household use has a voltage of in about 1.5 years’ time (only a fraction of the approximately 120 or 240 (in the USA). AC is easy to transmit typical warranty period), depending on module over long distances, but it is impossible to store. Most house- type, installation climate, and other conditions. hold appliances require this kind of electricity. Now, in all honesty, this information comes to us DC (direct current)—This is electricity that flows in one courtesy of the module manufacturers. The Na- direction only. PV modules, small wind turbines, and small tional Renewable Energy Laboratory has done hydroelectric turbines produce DC power, and batteries of all some impartial studies on payback time (see kinds store it. Appliances that operate on DC very rarely will the results at www.nrel.gov/ncpv/pdfs/24596 operate directly on AC, and vice versa. Conversion devices are .pdf). It concludes that modules installed under necessary. average U.S. conditions reach energy payback in three to four years, depending on construction inverter—An electronic device that converts (transforms) the type. The aluminum frame all by itself can ac- low-voltage DC power we can store in batteries to convention- count for six months to one year of that time. al 120-volt AC power as needed by lights and appliances. This Quicker energy paybacks, down to one to two makes it possible to utilize the lower-cost (and often higher- years, are expected in the future, as more “so- quality) mass-produced appliances made for the conventional lar grade” silicon feedstock becomes available, grid-supplied market. Inverters are available in a wide range and simpler standardized mounting frames are of wattage capabilities. We commonly deal with inverters that developed. have a capacity of anywhere between 150 and 6,000 watts. pV Module—A “solar panel” that makes electricity when ex- posed to direct sunlight. PV is shorthand for photovoltaic. We Maintenance call these panels PV modules to differentiate them from solar It’s almost laughable how easy the maintenance hot-water panels or collectors, which are a completely differ- is for PV modules. Because they have no mov- ent technology and are often what folks think of when we say ing parts, they are virtually maintenance free. “solar panel.” PV modules do not make hot water. Basically, you keep them clean. If it rains irregu- larly or if the birds leave their calling cards, hose solar living sourcebook 99
    • control technology is Maximum Power Point you all the conveniences of the typical 20-kWh- Tracking, or MPPT controls. These sophisti- per-day California home, while consuming less cated solid-state controllers allow the modules than 10 kWh per day. At $3,500 per installed SunShine to electricity to run at whatever voltage produces the maxi- kilowatt-hour, that’s $35,000 shaved off the ini- mum wattage. This is usually a higher voltage tial system cost! With this kind of careful analy- than batteries will tolerate. The extra voltage is sis applied to electrical use, most of the full-size down-converted to amperage the batteries can home electrical systems we design come in be- digest comfortably. MPPT controls extract an tween $15,000 and $30,000, depending on the average of about 15% more energy from your number of people and intended lifestyle. Simple PV array and do their best work in the winter- weekend cabins with a couple of lights and a The typical American time when most residential systems need all the boom box can be set up for $1,500 or less. With help they can get. Most controllers offer a few the renewable energy rebates and buydowns home consumes about other bells and whistles, like nighttime discon- available in an increasing number of states, 20-30 kilowatt-hours nect and LED indicator lights. See the Controls grid-tie PV can be very cost effective. Typical and Monitors section in Chapter 4 for a com- payback times in California run 6-12 years (an daily. Supplying this plete discussion of controllers. 8%-17% return on investment!). Commercial demand with PV- paybacks with tax incentives typically pay back in half that time. generated electricity can Powering Down Other chapters in this Sourcebook present an be costly; however, it The downside to all this good news is that the extensive discussion of electrical conservation, initial cost of a PV system is still high. After for both off and on grid (utility power), and of- makes perfect economic decades of cheap, plentiful utility power, we’ve fer many of the lights and appliances discussed. sense as a long-term turned into a nation of power hogs. The typical We strongly recommend reading these sections American home consumes about 20-30 kilo- before beginning system sizing. We are not pro- investment. watt-hours daily. Supplying this demand with posing any substantial lifestyle changes, just PV-generated electricity can be costly; however, the application of appropriate technology and it makes perfect economic sense as a long-term common sense. Stay away from 240-volt watt investment. Fortunately, at the same time that hogs, electric space heaters, cordless electric PV-generated power started to become afford- appliances, standard incandescent light bulbs, able and useful, conservation technologies instant-on TVs, and monster side-by-side re- for electricity started to become popular, and frigerators, and our friendly technical staff can given the steadily rising cost of utility power, work out the rest with you. even necessary. The two emerging technologies dovetail together beautifully. Every kilowatt- hour you can trim off your projected power PV Performance in use in a standalone (off-grid) PV-based system will reduce your initial setup cost by as much the Real World as $3,500. Using a bit of intelligence and care in Okay, here’s the dirt under the rug. Skeptics and your lighting and appliance selection will allow pessimists knew it all along: PV modules could not possibly be all that perfect and simple. Even the most elegant technology is never quite per- Photovoltaic Summary fect. There are a few things to watch out for, be- aDVaNtageS DiSaDVaNtageS ginning with . . . Wattage ratings on PV modules are given under ideal laboratory conditions. As- 1. No moving parts 1. High initial cost suming you can avoid or eliminate shadows, the 2. Ultralow maintenance 2. Works only in direct sunlight two most important factors that affect module 3. Extremely long life 3. Sensitive to shading performance out in the real world are percent- 4. Noncorroding parts 4. Lowest output during age of full Sun and operating temperature. 5. Easy installation shortest days 6. Modular design 5. Low-voltage output difficult ShaDoWS 7. Universal application to transmit Short of outright physical destruction, hard 8. Safe low-voltage output shadows are the worst possible thing you can do 9. Simple controls to a PV module. Even a tiny amount of shading 10. Long-term economic dramatically affects module output. Electron payback flow is like water flow. It flows from high volt- age to low voltage. Normally the module is high 100 gaiam real goods
    • and the battery, or load, is lower. A shaded por- rectly to the pump without any batteries), derate tion of the module drops to very low voltage. by 20%, or even by 30% for really hot summer Electrons from other portions of the module climates if you want to make sure the pump will SunShine to electricity and even from other modules in the array will run strongly in hot weather. find it easier to flow into the low-voltage shaded area than into the battery. These electrons just end up making heat and are lost to us. This is Module Mounting why bird droppings are a bad thing on your PV Modules will catch the maximum sunlight, and module. A fist-size shadow will effectively shut therefore have the maximum output, when they off a PV module. Don’t intentionally install your are perpendicular (at right angles) to the Sun. modules where they will get shadows during the This means that tracking the Sun across the prime midday generating time from 10 a.m. to 3 sky from east to west will give you more power p.m. Early or late in the day, when the Sun is at output. But tracking mounts are expensive and extreme angles, little power is being generated prone to mechanical and/or electrical problems, anyway, so don’t sweat shadows then. Sailors and PV prices have been coming down. Unless may find shadows unavoidable at times, but just you’ve got a summertime high-power applica- The best year-round keep them clear as much as practical. tion, like water pumping, tracking mounts don’t make a good investment anymore. angle for your modules Full SuN PV systems are most productive if the mod- is approximately equal As mentioned above, most of us seldom see ules are approximately perpendicular to the Sun at solar noon, the most energy-rich time of day to your latitude. 100% full-Sun conditions. If you are not getting full, bright, shadow-free sunlight, then your for a PV module. The best year-round angle for PV output will be reduced. If you are not get- your modules is approximately equal to your ting bright enough sunlight to cast fairly sharp- latitude. Because the angle of the Sun changes edged shadows, then you do not have enough seasonally, you may want to adjust the angle of sunlight to harvest much useful electricity. your mounting rack seasonally. In the winter, Most of us actually receive 80%-85% of a “full modules should be at the angle of your latitude Sun” (defined as 1,000 watts per square meter) plus approximately 10 degrees; in the summer, on a clear sunny day. High altitudes and desert your latitude minus a 10-degree angle is ideal. locations will do better on sunlight availability. On a practical level, many residential systems On the high desert plateaus, 105%-110% of full will have power to burn in the summer, and Sun is normal. They don’t call it the “sunbelt” seasonal adjustment may be unnecessary. for nothing. Generally speaking, most PV arrays end up on fixed mounts of some type. Tracking mounts teMperature are rarely used for residential systems anymore. The power output from all PV module types Small water-pumping arrays are the most com- fades somewhat at higher temperatures. This mon use of tracking mounts now. This rule is not a serious consideration until ambient of thumb is far from ironclad; there are many temperatures climb above 80°F, but that’s not good reasons to use either kind of mounting. uncommon in full Sun. The backs of modules For a more thorough examination, see the PV should be as well ventilated as practical. Al- Mounting section, which includes a large selec- ways allow some airspace behind the modules tion of mounting technologies. if you want decent output in hot weather. On the positive side of this same issue, all modules Proper Pv mounting plus 10° increase output at lower temperatures, as in the for winter angle. wintertime, when most residential applications can use a boost. We have seen cases when mod- plus 10° for ules were producing 30%-40% over specs on a summer clear, cold winter morning with a fresh reflec- tive snow cover and hungry batteries. As a general rule of thumb, we usually de- your latitude rate official manufacturer-specified “nameplate” PV module output by about 25%-30% (grid-tie S in degrees systems) to 40%-50% (off-grid, battery-based leVel GrounD systems) for the real world. For panel-direct systems (where the modules are connected di- solar living sourcebook 101
    • System Examples SunShine to electricity Following are several examples of photovoltaic- ately. Water delivered to the raised storage tank based electrical systems, starting from simple is your stored energy. The brighter the Sun, the and working up to complex. All the systems that faster the pump will run. This kind of system use batteries can also accept power input from (without battery storage) is called PV-direct and wind or hydro sources as a supplement or as the is the most efficient way to utilize PV energy. primary power source. PV-based systems con- Eliminating the electrochemical conversion of stitute better than 95% of Gaiam Real Goods’ the battery saves about 20%-25% of the energy, renewable energy sales, so the focus here will be a very significant chunk! However, PV-direct mostly on them. systems work only with DC motors that can use the variable power output of the PV mod- a SiMple Solar puMpiNg SySteM ule, and of course this simple system works only In this simple system, all energy produced by when the Sun shines. the PV module goes directly to the water pump. There’s one component of a PV-direct system No electrical energy is stored; it’s used immedi- you won’t find in other systems. The PV-direct controller, or Linear Current Booster (LCB), is Pv-direct water unique to systems without batteries. This solid- pumping PV modules state device will down-convert excess voltage into amperage that will keep the pump running under low-light conditions when it would oth- erwise stall. An LCB can boost pump output by as much as 40%, depending on climate and load conditions. We usually recommend them for float switch PV-direct pumping systems. For more information about solar pumping, storage tank see Chapter 7, “Water Development.” linear current booster a utility iNtertie SySteM Without BatterieS This is the simplest and most cost effective way to connect PV modules to regular utility power. well All incoming PV-generated electrons are con- verted to household AC power by the intertie in- verter and delivered to the main household cir- cuit breaker panel, where they displace an equal number of utility-generated electrons. That’s power you didn’t have to buy from the utility pump company. If the incoming PV power exceeds a utility intertie what your house can use at the moment, the ex- without batteries cess electrons will be forced out through your electric meter, turning it backward. If the PV power is insufficient, that shortfall is automati- solar power AC to grid cally and seamlessly made up by utility power. solar PV array It’s like water seeking its own level (except it’s really fast water!). When your intertie system is pushing excess power out through the meter, the utility is paying you regular electric rates for your excess power. You sell power to the utility during the daytime; it sells power back to you at AC utility meter night. This treats the utility grid like a big 100%- DC voltage efficient battery. However, if utility power fails, input main utility AC voltage breaker panel even if it’s sunny, your PV system will be shut off output for the safety of utility workers. 102 gaiam real goods
    • How Much PV Area to Equal U.S. Electric Production? SunShine to electricity here’s the simple answer: A square mile (5,280 x 5,280 feet) equals 27,878,400 A solar-electric array, using today’s off-the-shelf tech- square feet. Divided by 23 square feet per module, nology, sited in sunny, largely empty Nevada, that’s big we can fit 1,212,104 modules per square mile. At enough to deliver all the electricity the U.S. currently 0.966 kilowatt-hours per module per day, our square uses, would cover a square almost exactly 100 miles mile will deliver 1,170,971kWh per day on aver- per side. age, or 427,404,328kWh per year. Back to our goal of 4,038,000,000,000kWh divided by 427,404,328kWh per here’s the proof in more detail: year per square mile, it looks like we need about 9,448 According to the Energy Information Administration of square miles of surface to meet the electrical needs of the U.S. Department of Energy, www.eia.doe.gov/emeu/ the United States. That’s a square area about 97 miles on aer/txt/ptb0802a.html, the U.S. produced 4,038 billion a side. This is about 60% of the approximately 16,000 kilowatt-hours of electricity in 2005. square miles currently occupied by Note that this is “production,” not the Nevada Test Site and the sur- “use.” Transmission inefficiencies and rounding Nellis Air Force Range other losses are covered. N e VA D A (www.nv.doe.gov/nts/ and www. We’ll want our PV modules in a nellis.af.mil/ environmental/default. sunny area to make the best of our in- htm). vestment. Nevada, thanks to climate What about the cost/benefit of and military/government activities, such a project? Let’s look at the has a great deal of almost empty and cost of an array that would produce very sunny land. So looking at the This area— just one-quarter of the required National Solar Radiation Data Base the nevada electricity that is produced in the Test site and nellis for Tonopah, Nevada http://rredc air Force base—could U.S. Currently small commercial or .nrel.gov/solar/pubs/redbook/, a deliver twice the needed residential systems cost about $5- flat-plate collector on a fixed mount energy to meet the entire $6 per peak watt including typical facing south at a fixed tilt equal to u.s. needs, using existing government and utility incentives. If the latitude, 38.07° in this case, saw a photovoltaic technology. economies of scale, advances in ef- yearly average of 6.1 hours of “full- ficiencies, and government subsidies sun” per day in the years 1961 through 1990. A “full- are considered, the job might get done for $2/watt (just sun” is defined as 1,000 watts per square meter. guessing here, but you get the idea). Therefore, our For PV modules, we’ll use the large Sharp 208-watt quarter-sized 596,000 megawatt array would cost a cool module, which the California Energy Commission, $1.19 trillion. This certainly is a lot of money; but then www.energy.ca.gov/ greengrid/certified_pv_modules the potential benefits can be enormous. For one, think .html, rates at 183.3 watts output, based on lab-tested of the jobs created. The Apollo Alliance (www.apolloal- performance. 183.3 watts times 6.1 hours equals 1,118 liance.org) says that “Renewable power production is watt-hours or 1.118 kilowatt-hours per day per module labor intensive. . . . Solar PV creates 7.24 jobs per MW.” at our Tonopah site. At 65 x 39 inches this module However, worldwide PV production in 2005 was only presents 17.6 square feet of surface area. We’ll allow 1,652 megawatts (www.solarbuzz.com), so we’ve got a some space between rows of modules for maintenance ways to go to meet this potential demand. access and for sloping wintertime Sun, so let’s say that As a practical measure, PV power production hap- each module will need 23 square feet. pens during the daytime, and so long as we use lights Conversion from PV module DC output to conven- at night, we will continue to use substantial power at tional AC power isn’t perfectly efficient. Looking at the night. Also, out in the desert, solar thermal collection real-world performance figures from the California may be a more efficient power generation technology. Energy Commission, www.energy.ca.gov/greengrid/ But however you run the energy collection system, certified_invert ers.html, we see that the SatCon Power large solar-electric farms on what is otherwise fairly Systems 75kW model AE-75-60-PV-D is rated at 96% useless desert land could add substantially to the efficiency. We’ll probably be using larger inverters, electrical independence and security of any country. but this is a typical efficiency for large intertie invert- The existing infrastructure of coal, nuclear, and hydro ers. We’d better also deduct about 10% for whatever power plants could continue to provide reliable power other losses might occur—dirty modules, etc. So our at night, but nonrenewable resource use and carbon 1.118kWh per module per day becomes 0.966kWh by dioxide production would be greatly reduced. the time it hits the AC grid. solar living sourcebook 103
    • could drive a car without any gauges, warning lights, or speedometer—but this doesn’t encour- age system reliability or longevity. SunShine to electricity The Real Goods Weekend Getaway Kit is an example of a small-cabin or weekend retreat system. It has all the basic components of a resi- dential power system: A power source (the PV module), a storage system (the deep-cycle bat- tery), a controller to prevent overcharging, safe- ty equipment (fuses), and monitoring equip- ment. The Weekend Getaway Kit (see p. 115) is supplied as a simple DC-only system. It will run 12-volt DC equipment, such as RV lights and appliances. An optional inverter can be added at any time to provide conventional AC power, and that takes us to our next example. a Full-Size houSeholD SySteM small cabin systems Let’s look at an example of a full-size residen- to run a few lights and There is a minimum of hardware for these tial system to support a family of three or more. an appliance intertie systems; a power source (the PV mod- The power source, storage, control, monitoring, or two can start at ules), an intertie inverter, a circuit breaker, and under $1,000. and safety components have all been increased some wiring to connect everything. See the sep- in size from the small-cabin system, but most arate section specifically on Utility Intertie for important, we’ve added an inverter for conven- more information. tional AC power output. The majority of house- a SMall CaBiN pV SySteM hold electrical needs are run by the inverter, With BatterieS allowing conventional household wiring and a greater selection in lighting and appliance Most PV systems are designed to store some of choices. We’ve found that when the number of the collected energy for later use. This allows lights gets above five, AC power is much easier you to run lights and entertainment equipment to wire, plus fixtures and lamps cost significant- at night, or to temporarily run an appliance that ly less due to mass production, so the inverter takes more energy than the PV system is deliver- pays for itself in appliance savings. ing. Batteries are the most cost-effective energy Often, with larger systems like this, we com- storage technology available so far, but batter- bine and preassemble all the safety, control, and ies are a mixed blessing. The electrical/chemical inverter functions using an engineered, UL- conversion process isn’t 100% efficient, so you Batteries are the have to put back about 20% more energy than approved power center. This isn’t a necessity, but we’ve found that most folks appreciate the most cost-effective you took out of the battery, and the storage ca- pacity is finite. Batteries are like buckets, they energy storage can get only so full and can empty just so far. A The typical real goods full-time system takes only 4’x8’ of floor space inside your utility room. technology available so charge controller becomes a necessary part of your system to prevent over- (and sometimes far, but batteries are a under-) charging. Batteries can also be danger- mixed blessing. ous. Although the lower battery voltage is gen- erally safer to work around than conventional AC house current, it is capable of truly awe-in- spiring power discharges if accidentally short- circuited. So fuses and safety equipment also become necessary whenever you add batteries to a system. Fusing ensures that no youngster, probing with a screwdriver into some unfor- tunate place, can burn the house down. And finally, a monitoring system that displays the battery’s approximate state of charge is essential for reliable performance and long battery life. Monitoring could be done without—just as you 104 gaiam real goods
    • Handy Formulas for Estimating SunShine to electricity Household Renewable Energy Installations [Photovoltaic (PV) array size (watts)] x [solar Wind = 7¢/kWh radiation (hours/day)] x [system efficiency] = PV = 14¢/kWh (Real Goods residential cost) [system output (watt-hours/day)] Hydro = 11¢/kWh Geothermal = 11¢/kWh off-grid Solar Nuclear = 14¢/kWh [Average daily electric usage (watt-hours/day)] ÷ Centralized PV = 15¢/kWh [solar radiation (hours/day)] ÷ [55% off-grid (Source: “Solar Revolution” by Travis Bradford) system efficiency] = [PV watts required] Ballpark estimate: In 2005, about 50% of the electricity produced in [PV array size (W)] x 3 = [Output (Wh/day)] the U.S. was from coal, 20% from nuclear, 16% from [Output (Wh/day)] x ⅓ = [PV array size (W)] natural gas, and 10% from renewables (mostly hydro). Only about one-third of this power actually reached on-grid Solar the consumer—the rest was lost along the way (due to [Average daily electric usage (kilowatt-hours/day)] conversion, transmission, distribution, etc.). Source: ÷ [solar radiation (hours/day)] ÷ [70% on-grid eia.doe.gov. system efficiency] = [PV kilowatts required] Ballpark estimate: Battery Bank Sizing [PV array size (kW)] x 4 = [Output (kWh/day)] [kWh/day] x [3-5 days of storage] x 3 = [Output (kWh/day)] x ¼ = [PV array size (kW)] [kWh size for battery bank] 1kW = 75 sq. ft. of PV panels Charge Controller Sizing 1MW (system rating) of PV energy powers 130 [PV Short-circuit current amps] x 1.56 = homes at the U.S. average of 31kWh/day (220 [Total amp size] homes in California at 18kWh/day average) 1MW (system rating) of wind energy powers 250 Fusing/Breakers Sizing average U.S. homes (450 homes in California) [Short-circuit current amps] x 1.56 = [Fuse/breaker amp size] Wholesale Cost of producing electricity Coal = 4¢/kWh Natural gas = 6¢/kWh tidy appearance, fast installation, UL approval, household and maintain full charge on an emer- and ease of future upgrades that preassembled gency back-up battery bank is fed back into the power centers bring to the system. utility grid, earning money for the system own- Because family sizes, lifestyles, local climates, er. If household power requirements exceed the and available budgets vary widely, the size and PV input, e.g., at night or on a cloudy day, the components that make up a larger residential shortfall is automatically and seamlessly made system are customized for each individual ap- up by the grid. If the grid power fails, power will plication. System sizing is based on the custom- be drawn instantly from the back-up batteries er’s estimate of needs and an interview with one to support the household. Switching time in of our friendly technical staff. See the “System case of grid failure is so fast that only your home Sizing” hints and worksheets in Chapter 4 or in computer may notice. This is the primary differ- the Appendix. ence between intertie systems with and without batteries. Batteries will allow continued opera- a utility iNtertie SySteM tion if the utility fails. They’ll provide back-up With BatterieS power for your essential loads and will allow In this type of intertie system, the customer has you to store and use any incoming PV energy. both a renewable energy system and conven- A number of federal and state programs ex- tional utility-supplied grid power. Any renew- ist to hasten this emerging technology, and an able energy beyond what is needed to run the increasing number of them have real dollars to solar living sourcebook 105
    • SunShine to electricity a full-size household system has all these spend! These dollars usually appear as refunds, technical staff, with over 60,000 solar systems parts. buydowns, or tax credits to the consumer— under its collective belt, has become rather that’s you. Programs and available funds vary good at this. We don’t charge for this personal with time and state. For the latest information, service, so long as you purchase your system call your State Energy Office, listed in the Ap- components from us. We do need to know what pendix, or check the Database of State Incen- makes your house, site, and lifestyle unique. So tives for Renewable Energy on the Internet at filling out the household electrical demands www.dsireusa.org. portion of our sizing worksheets is the first very necessary step, usually followed by a phone call (whenever possible) and a customized system System Sizing quote. Worksheets, wattage charts, and other We’ve found from experience that there’s no helpful information for system sizing are in- such thing as “one size fits all” when it comes cluded at the end of Chapter 4, our “panel to to energy systems. Everyone’s needs, expecta- plug” chapter—which also just happens to cover tions, budget, site, and climate are individual, batteries, safety equipment, controls, monitors, and your power system, in order to function and all the other bits and pieces you need to reliably, must be designed with these individual know a little about to assemble a safe, reliable factors accounted for. Our friendly and helpful renewable energy system. What’s It Going to Cost Me to Go Solar? three easy steps to get a ballpark calcula- able in your state. For instance, in California, tion for utility-tied systems:* you can multiply your gross installed cost by 1. Find your daily utility usage by divid- 0.65 to account for rebates and tax credits. In ing the kilowatt-hours (kWh) used on an New York or New Jersey, multiply by 0.5. For average month’s utility bill by 30. commercial systems, multiply by 0.3. 2. Divide that number by 5 (the aver- What ongoing savings can i expect? age number of peak Sun hours in the U.S.) Whatever you’re now paying the utility for and multiply by 1.43 to account for system electricity will change to $0 (service charges losses. This is the size of the solar system, in will still apply). kilowatts, that you will need for taking care of 100% of your electrical needs. Call our techs at 800-919-2400 for more 3. Multiply that number by $9,000 ($9/ information on how solar can work for your watt installed) for a good ballpark idea of the house. gross installed cost. Can state rebate incentives take a chunk *For off-grid systems, roll up an estimated out of that price? Go to www.dsireusa.org to watt-hour calculation using our system sizing find out what grants or incentives are avail- worksheet on pages 173-175 or page 579. 106 gaiam real goods
    • Photovoltaic Mounting Hardware SunShine to electricity A PV mounting structure will secure your mod- the falling cost of PV modules makes trackers ules from wind damage and lift them slightly to less attractive. For most systems now, an extra allow some cooling air behind them. Mounts module or two on a simple fixed mount is a can be as small as one module for an RV or big much better investment in the long run. enough to carry hundreds of modules for a util- In the following pages, you’ll find numerous ity intertie system. PV systems are most pro- mounting structures, each with its own particu- ductive if the modules are approximately per- lar niche in an independent energy system. We’ll pendicular to the Sun at solar noon, the most try to explain the advantages and disadvantages energy-rich time of the day for a PV module. If of each style to help you decide if a particular you live in the Northern Hemisphere, you need mount belongs in your system. to point your modules roughly south. The best In ascending order of complexity, your year-round angle for your modules is approxi- choices are: mately equal to your latitude. For better winter • RV Mounts performance, raise that angle about 10°; for • Home-Built Mounts better summer performance, lower that angle • Fixed Roof or Ground Mounts about 10°. • Top-of-Pole Fixed Mounts • Passive Trackers plus 10° for winter • Active Trackers plus 10° RV Mounts for Because of wind resistance and never knowing summer which direction the RV will be facing next, most RV owners simply attach the module(s) flat on the roof. RV mounts raise the module an inch your latitude or two off the roof for cooling. They can be used S in degrees for small home systems as well. Simple and in- The best year-round leVel GrounD expensive, most of them are made of aluminum angle for your modules for corrosion resistance. Obviously, they’re built is approximately Proper Pv mounting angle to survive high wind speeds. These are a good choice for systems with a module or two. For equal to your latitude. Off-the-grid systems should probably have larger systems, the fixed or pole-top racks are For better winter the modules oriented for best wintertime per- usually more cost effective. formance, as this is typically when they are performance, raise most challenged for power delivery. On-grid, HoMe-Built Mounts that angle about 10°; utility-intertied systems are usually set up for Want to do it yourself? No problem. Small fixed best summer performance. Most utilities allow racks are pretty easy to put together. Anodized for better summer credits to be rolled over from one month to the aluminum or galvanized steel are the preferred performance, lower that next. We’ll make the most of those long summer materials due to corrosion resistance, but mild days to deliver the maximum kilowatt-hours for steel can be used just as well, so long as you’re angle about 10°. the year. willing to touch up the paint occasionally. Slot- You can change the tilt angle of your array ted steel angle stock is available in galvanized seasonally as the Sun angle changes, but on a form at most hardware and home-supply stores practical level, many residential systems will have and is exceptionally easy to work with. Wood power to burn in the summer. Most folks have is not recommended, because your PV modules found seasonal adjustments to be unnecessary. will last longer than any exposed wood. Even The perfect mounting structure would aim treated wood won’t hold up well when exposed the PV array directly at the Sun and follow it to the weather for over 40 years. Make sure across the sky every day. Tracking mounts do that no mounting parts will cast shadows on this, and in years past, Real Goods has enthusi- the modules. Adjustable tilt is nice for seasonal astically promoted trackers. But times change. angle adjustments, but most residential systems The electrical and/or mechanical complexity of have power to spare in the summer, and sea- tracking mounts assures you of ongoing main- sonal adjustments are usually abandoned after tenance chores (ask us how we know . . .), and a few years. solar living sourcebook 121
    • Fixed RooF oR GRound Mounts snow off of them is sometimes troublesome; it This is easily the most popular mounting struc- can pile up at the base. Ground mounting can leave the modules vulnerable to grass growing SunShine to electricity ture style we sell. These all use the highly adapt- able SolarMount extruded aluminum rails up in front, or to rocks kicked up by mowers. as their base. This à la carte mounting system A foot or so of elevation or a concrete pad is a offers the basic rails in various lengths and good idea for ground mounts. Note that attach- strengths (Lite or Standard). Buy enough rails ing these racks to the roof will require roof pen- to fit your particular array, then add optional etrations every 4-6 feet. For example, a 3kW PV roof standoffs and/or telescoping back legs array might need 20-24 support points, so the for seasonal tilt and variable roof pitches. This skill of the installer is important here to ensure mounting style can be used for flush roof arrays, a leak-free roof. low-profile roof arrays with a modest amount For larger, flat roof-mounted systems (usu- of tilt, high-profile arrays that stand way up, ally on commercial buildings), several bal- ground mounts in either low or high profile, last-type racks are available these days. If roof or even flipped over on south-facing walls. Use penetrations are undesirable, then securing the concrete footings or a concrete pad for ground mounting hardware with heavy weights (such mounts. The racks are designed to withstand as concrete blocks or containers of sand) or the wind speeds up to 100 miles per hour or more. weight of the hardware—ballasts—is the an- They don’t track the Sun, so there’s nothing to swer. The disadvantage of this type of mounting wear out or otherwise need attention. Getting is usually the high cost, even though installation is not too difficult. High-wind or seismic areas will probably also require some sort of mechan- Do Tilt Angle or Orientation Matter? ical attachment to the roof anyway. Finally, a mention of BIPV (Building Inte- M uch has been made in years past of PV tracking and tilt angle. You would think that it’s nearly a life-or-death matter to point your PV modules directly at the Sun during all grated PV) products should be included here, even though these roof PV modules don’t re- quire mounting hardware at all. Intended pri- times of the day. We’re here to shake up this belief. Tilt angle marily for new construction, these modules and orientation make a lot less difference than most folks actually are part of the roof covering. They pro- believe. vide an architecturally pleasing look that blends From the Sandia National Labs comes this very interesting in seamlessly with the rest of the home or build- chart, which details tilt angle vs. compass orientation, and the ing. One type is the frameless roof-integrated resulting effect on yearly power production. South-facing, at module, such as the UniSolar Shingle, which a 30° angle (7:12 roof pitch) delivered the most energy. They looks much like a typical composition shingle. labeled that point 100%. All other orientations and tilt angles Another type is more like a standard framed are expressed as a percentage of that number. Note that we can polycrystalline module but is sized and installed face SE or SW, a full 45° off due south, and lose only 4%. Our like a roof tile. The main advantage of BIPV tilt angle can be 15° off, and we lose only 3%. In reality, we products is that they are unobtrusive and usu- can face due east or west and lose only 12%! A couple of bird ally look pretty good if aesthetics are important. droppings could cost you more energy. Disadvantages include their higher cost and low efficiency due to higher operating temperatures RooF slope and oRientation (northern California data) (lack of cooling air circulation). For more infor- Flat 4:12 7:12 12:12 21:12 Vertical (0°) (18.4°) (30°) (45°) (60°) (90°) mation about BIPV and ballast mounts, be sure south 0.89 0.97 1.00 0.97 0.89 0.58 to call one of our Solar Technicians. sse, ssW 0.89 0.97 0.99 0.96 0.88 0.59 se, sW 0.89 0.95 0.96 0.93 0.85 0.60 top-oF-pole Fixed Mounts ese, WsW 0.89 0.92 0.91 0.87 0.79 0.57 A popular and cost-effective choice, pole-top east, West 0.89 0.88 0.84 0.78 0.70 0.52 mounts are designed to withstand winds up to 80 mph and in some cases up to 120 mph. The moral of this story? Shadows, bird droppings, leaves, The UniRac rails for the larger pole-top arrays and dirt will have far more effect on your PV output than ori- are a heavier-duty version of the standard So- entation. Keep your modules clean and shade free, and don’t larMount rails. This mounting style is a good worry if they aren’t perfectly perpendicular to the Sun at noon choice for snowy climates. With nothing under- every day. You’ll do fine. neath it, snow tends to slide right off. For small or remote systems, pole-top mounts are the least expensive and simplest choice. We 122 gaiam real goods
    • To Track or Not to Track add very little in winter unless you live in the extreme southern U.S., water-pumping projects, the most cost-effective way to increase daily SunShine to electricity P hotovoltaic modules produce the most energy when situated perpendicular to the Sun. A tracker or even further south. Trackers need clear access to the Sun from production is to simply add a track- ing mount. early in the morning until late in If your projects peaks in power is a mounting device that follows the afternoon. A solar window from use during winter, such as power- the Sun from east to west and keeps 9 a.m. to 4 p.m. is workable; if you ing a typical house, then tracking the modules in the optimum posi- have greater access, more power to doesn’t offer you much. In most of tion for maximum power output. you (literally). North America, winter tracking will At the right time of year, and in the Tracking mounts are expensive, add less than 15%. One of the new right location, tracking can increase and PV power is getting cheaper. generation of MPPT charge con- daily output by more than 30%. But If you have a project that peaks trols is a much better investment beware of the qualifiers: Trackers in power use during the summer, in this situation. They add 15%- are often not a good investment. such as water pumping or resi- 30% and do their best work in the Trackers work best during the dential cooling, then tracking may winter. See the Controllers section height of summer, when the Sun is be a very good choice. For many of Chapter 4 for more info. making a high overhead arc. They almost always use these for one- or two-mod- Make sure that your pole is tall enough to al- ule pumping systems. Tilt and direction can be low about one-third burial depth and still clear easily adjusted. Site preparation is easy, just get livestock, snow, or weeds. Ten feet total for your steel pipe cemented in straight. The pole pole length is usually sufficient. Taller poles are is common schedule 40 steel pipe, which is not sometimes used for theft deterrence. Pole diam- included (pick it up locally to save on freight). eter depends on the specific mount and array solar living sourcebook 123
    • Based on our size. Pole sizes listed are for “nominal pipe size.” over toward the east. In winds over 15 mph, the For instance, what the plumbing industry calls passive tracker may be blown off course. These experience, the “4-inch” is actually 4½-inch outside diameter. trackers can withstand winds of up to 85 mph SunShine to electricity experience of hundreds When a mount says it fits “4-inch,” it’s actually (provided you follow the manufacturer’s rec- expecting a 4½-inch-diameter pipe. ommendations for burying the pipe mount) but of customers, and will not track at high wind speeds. If you have passiVe tRaCkeRs routine high winds, you should have a wind tur- the dropping price Tracking mounts will follow the Sun from east bine to take advantage of those times, but that’s of PV power, we no to west across the sky, increasing the daily power a different subject. longer recommend output of the modules, particularly in summer and in southern latitudes. Trackers are most of- aCtiVe tRaCkeRs active trackers. Their ten used on water-pumping systems with peak Active trackers use photocells, electronics, and high initial cost and demands in summer. See the sidebar “To Track linear actuators like those on giant old-fash- or Not to Track” for a discussion on when track- ioned satellite TV dishes to track the Sun very continuing maintenance ing mounts are appropriate. accurately. A small controller bolted to the array problems just aren’t Passive trackers follow the Sun from east to is programmed to keep equal illumination on west using just the heat of the Sun and gravity. the photocells at the base of an obelisk. Power worth the investment No source of electricity is needed—a simple, ef- use is minuscule. Active trackers average slight- any longer. Want more fective, and brilliant design solution. The north- ly more energy collection per day than a passive south tilt axis is seasonally adjustable manu- tracker in the same location, but historically power? Add some more ally. Maintenance consists of two squirts with a they have also averaged more mechanical and PV. It’s hard to beat grease gun once every year. electrical problems, too. Based on our experi- Tracking will boost daily output by about ence, the experience of hundreds of customers, the reliability of 30% in the summer and 10%-15% in the winter. and the dropping price of PV power, we no lon- no moving parts. The two major problems with passive technol- ger recommend active trackers. Their high ini- ogy are wind disturbances and slow “wake-up” tial cost and continuing maintenance problems when cold. The tracker will go to “sleep” facing just aren’t worth the investment any longer. west. On a cold morning, it may take more than Want more power? Add some more PV. It’s hard an hour for the tracker to warm up and roll to beat the reliability of no moving parts. 124 gaiam real goods
    • Wind and Hydro Power Sources SunShine to electricity Sunlight, wind, and falling water are the renew- during certain times of the year or when storms able energy big three. These are energy sources are passing through. Tower height and location that are commonly available at a reasonable also make a big difference. Wind speeds aver- cost. Solar, or sunlight, the single most common age 50%-60% higher at 100 feet compared with and most accessible renewable energy source, is ground level (see chart in the Wind section). well covered at the beginning of this chapter. Wind systems these days are almost always We’ve found in our years of experience that designed as wind/solar hybrids for year-round wind and hydro energy sources are most often reliability. The only common exceptions are developed as a booster or bad-weather helper systems designed for utility intertie; they feed for a solar-based system. These hybrid systems excess power back into the utility and turn the Wind and hydro have the advantage of being better able to cover meter backward. power needs throughout the year and are less energy sources are expensive than a similar capacity system using most often developed only one power source. When a storm blows Hydroelectric Systems through, the solar input is lost, but a wind gen- For those who are lucky enough to have a good as a booster or bad- erator more than makes up for it. The short, site, hydro is really the renewable energy of weather helper for a rainy days of winter may limit solar gain, but choice. System component costs are much low- the hydro system picks up from the rain and de- er, and watts per dollar return is much greater solar-based system. livers steady power 24 hours a day. This is not for hydro than for any other renewable source. These hybrid systems to say that you shouldn’t develop an excellent The key element for a good site is the vertical single-source power system if you’ve got it—like distance the water drops. A small amount of have the advantage a year-round stream dropping 200 feet across water dropping a large distance will produce as of being better able your property, for instance. But for most of us, much energy as a large amount of water drop- we’ll be further ahead if we don’t put all our eggs ping a small distance. The turbine for the small to cover power needs in one basket. Diversify! amount of water is going to be smaller, lighter, throughout the year Our experienced technical staff is well versed easier to install, and vastly cheaper. We offer in supplying the energy needs of anything from several turbine styles for differing resources. and are less expensive a small weekend getaway cabin all the way up to The small Pelton wheel Harris systems are well than a similar capacity an upscale state-of-the-art resort. We’ll be glad suited for mountainous territory that can deliver to help put a system together for you. There is some drop and high pressure to the turbine. The system using only usually no charge for our friendly and personal- propeller-driven Low Head Stream Engine is one power source. ized services. for flatter sites with less drop but more volume, and the Stream Engine, with a turgo-type run- ner, falls in between. It can handle larger water Wind Systems volumes and make useful power from shorter We generally advise that a good, year-round vertical water-drop distances. wind turbine site isn’t a place that you’d want Read on for detailed explanations of wind to live. It takes average wind speeds of 8-9 mph generators and hydro turbines. If you need a lit- and up to make a really good site. That’s hon- tle help and guidance putting a system together estly more wind than most folks are comfort- or simply upgrading, our technical staff, with able living with. But this is where the beauty decades of hands-on experience in renewable of hybrid systems comes in. Many very livable energy, will be glad to help. Call us toll-free at sites do produce 8-mph and greater wind speeds 800-919-2400. solar living sourcebook 131
    • Hydroelectricity SunShine to electricity If you could choose any renewable energy source you wanted, hydro is the one. If you What Is a “Good” Hydro Site? Hydropower, don’t want to worry about a conservation-based The Columbia River in the Pacific Northwest has given the right site, lifestyle—always nagging your kids to turn off some really great hydro sites, but they’re not ex- the lights, watching the voltmeter, basing every actly homestead scale (or low cost). Within the can cost as little as a appliance decision on energy efficiency—then hydro industry, the kind of home-scale sites and tenth of a PV system of you had better settle next to a nice year-round systems we deal with are called micro-hydro. mountain stream! Hydropower, given the right The most cost-effective hydro sites are located comparable output. site, can cost as little as a tenth of a PV system of in the mountains. Hydropower output is deter- comparable output. Hydropower users are often mined by water’s volume times its fall or drop able to run energy-hog appliances that would (jargon for the fall is “head”). You can get ap- proximately the same power output by running 1,000 gallons per minute through a 2-foot drop as by running 2 gallons per minute through a 1,000-foot drop. In the former scenario, where lots of water flows over a little drop, we are deal- ing with a low-head/high-flow situation, which is not truly a micro-hydro site. Turbines that can efficiently handle thousands of gallons are usu- ally large, bulky, expensive, and site specific. But if you don’t need to squeeze every last available watt out of your low-head source, the Low-Head Stream Engine generator will produce very use- ful amounts of power from low-head/high-flow sites, or the Turgo runner used on the Stream Engine is good at high-volume sites with 15 feet or more of head. High-head installation low-head installation bankrupt a PV system owner, like large side-by- side refrigerators and electric space heaters. Hy- dropower will probably require more effort on- site to install, but even a modest hydro output Small hydro systems over 24 hours a day, rain or shine, will add up are well worth to a large cumulative total. Hydro systems get by with smaller battery banks because they need developing, even if to cover only the occasional heavy power surge used only a few months rather than four days of cloudy weather. Hydro turbines can be used in conjunction out of the year, if those with any other renewable energy source, such months coincide as PV or wind, to charge a common battery bank. This is especially true in the West, where with your highest seasonal creeks with substantial drops flow only power needs. in the winter. This is when power needs are at their highest and PV input is at its lowest. Small hydro systems are well worth developing, even if used only a few months out of the year, if those months coincide with your highest power needs. So, what makes a good hydro site, and what else do you need to know? 132 gaiam real goods
    • For hilly sites that can deliver a minimum ment work, this simple turbine can provide for of 50 feet of head, Pelton wheel turbines offer a modest homestead. the lowest-cost generating solution. The Pelton- If you’d rather look into the typical low-head SunShine to electricity equipped Harris turbine is perfect for low-flow/ scenario, contact the DOE’s Renewable Energy high-head systems. It can handle a maximum Clearinghouse at 800-363-3732, or use Internet of 200 gallons per minute and requires a mini- access at www1.eere.energy.gov/windandhydro/ mum 50-foot fall to make useful amounts of hydro_engineer_analysis.html or www.micro power. In general, any site with more than 100 hydropower.net for more free information on feet of fall will make an excellent micro-hydro low-head hydro than you ever thought was site, but many sites with less fall can be very possible. productive also. The more head, the less volume will be necessary to produce a given amount of power. Check the output charts in the Products How Do Micro-Hydro section for a rough estimate of what your site Systems Work? can deliver. The basic parts of micro-hydro systems are A hydro system’s fall doesn’t need to happen the pipeline (called the penstock in the trade), all in one place. You can build a small collection dam at one end of your property and pipe the which delivers the water; the turbine, which For the homestead with transforms the energy of the flowing water into water to a lower point, collecting fall as you go. rotational energy; the alternator or generator, a good creek but little It’s not unusual to use several thousand feet of pipe to collect a hundred feet of head (vertical which transforms the rotational energy into significant fall, the Low- electricity; the regulator, which controls the fall). generator or dumps excess energy, depending Head Stream Engine Our Hydro Site Evaluation service will es- timate output for any site, plus it will size the on regulator style; and the wiring, which de- turbine is a far less piping and wiring, and factor in any losses from costly alternative. pipe friction and wire resistance. See the exam- ple at the end of this editorial section. What If I Have a High-Flow/Low-Head Site or Want AC Output? Typically, high-flow/low-head or AC-output hydro sites will involve engineering, custom metalwork, formed concrete, permits, and a fair amount of initial investment cash. None of this is meant to imply that there won’t be a good payback, but it isn’t an undertaking for the Typical micro-hydro system faint-of-heart or thin-of-wallet. AC generators livers the electricity. Our micro-hydro systems are typically used on larger commercial systems, also use batteries, which store the low-voltage or on utility intertie systems. DC generators are DC electricity, and usually an inverter, which typically used on smaller residential systems. converts the low-voltage DC electricity into 120 DC generation systems offer several ad- or 240 volts AC electricity. vantages for small hydro. Control is easy and Most micro-turbine systems use a small DC cheap. The batteries we’ll use to store energy alternator or generator to deliver a small but allow power output surges way over what the steady energy flow that accumulates in a bat- turbine is delivering. The DC-to-AC inverters tery bank. This provides a few important ad- now available will deliver far cleaner and more vantages. The battery system allows the user to tightly regulated AC power than a small AC hy- store energy and expend it, if needed, in short dro turbine can manage, and the inverter will powerful bursts (like a washing machine start- cost less than a small AC control system. ing the spin cycle). The batteries will allow us to For the homestead with a good creek but deliver substantially more energy for short peri- little significant fall, the Low-Head Stream En- ods than a turbine is producing, as long as the gine turbine is a far less costly alternative. With battery and inverter are designed to handle the just 3 or 4 feet of fall, and some site develop- load. DC charging means that precise control of solar living sourcebook 133
    • The bottom line is that alternator speed is not needed, as is required for 60-Hz AC output. This saves thousands of dol- a DC-based system lars on control equipment. And finally, with the SunShine to electricity will cost far less than quality of the DC-to-AC inverters now available, you’ll enjoy cleaner, more tightly controlled AC an AC system for most power through an inverter than through a small residential users, and AC turbine. The bottom line is that a DC-based system will cost far less than an AC system for will perform better. most residential users, and will perform better. DC Turbines an 1880s vintage single-nozzle Pelton wheel. only the generator technology has changed. Several micro-hydro turbines are available with simple DC output. We currently offer the Harris required. The typical American home consumes and the Stream Engine. 15-25kWh per day with no particular energy conservation, so with a good hydro site, it is HaRRis tuRBine fairly easy to live a conventional lifestyle. The Harris turbine uses a hardened cast-sili- The Harris turbine can be supplied with one, cone bronze Pelton turbine wheel mated with two, or four nozzles. The maximum flow rate a low-voltage DC alternator. Pelton wheel tur- for any single nozzle can be from 20 to 60 gal- bines work best at higher pressures and lower lons per minute (gpm), depending on the head volumes. Life begins at about 50 feet of head for pressure. The turbine can handle flow rates to these turbines and has no practical upper limit. about 120 gpm before the sheer volume of wa- Harris offers a couple choices for the alterna- ter starts getting in its own way. Many users tor. The standard Harris is based on common buy two- or four-nozzle turbines with different- 1970s Motorcraft alternators with windings that sized nozzles, so that individual nozzles can be are customized for each individual application. turned on and off to meet variable power needs Bearings and brushes will require replacement or water availability. The brass nozzles are easily at intervals from one to five years, depending replaceable because they eventually wear out, on how hard the unit is working. These parts especially if there is grit in the water. They are are commonly available at any auto parts store. available in 1∕16-inch increments, from 1∕16 inch Harris now comes with a standard permanent- through ½ inch. The first nozzle doesn’t have a magnet alternator that is custom made. The PM shutoff valve, while all nozzles beyond the first alternators deliver more power under almost all one are supplied with ball valves for easy, visible conditions, have no brushes to wear out, and are operation. mounted on larger, more robust bearings with two to three times the life expectancy. stReaM enGine Depending on the volume and fall supplied, The Stream Engine turbines use a unique brush- Harris turbines can produce from 1kWh (1,000 less, permanent-magnet alternator with three watt-hours) to 35kWh per day. Maximum al- large sealed-shaft bearings. Permanent magnets ternator instantaneous output is about 2,500 mean there are no field brushes to wear out. watts in a 48-volt system with cooling options Magnetic field strength is adjusted by varying the air gap between the magnet disk and the stationary alternator windings. Once the unit is set up, there is almost no routine maintenance required. Setup requires some time with this universal design, however, and involves trial Two- and four-nozzle and adjustment: selecting one of four alterna- Harris turbines. The tor wiring setups and then adjusting the perma- four-nozzle is upside nent-magnet rotor air gap until peak output is down to show the Pelton wheel and achieved. A precision shunt and digital multi- nozzles. meter are supplied to expedite this setup pro- cess. Output voltage can be user selected at 12, 24, or 48 volts. Maximum instantaneous output is 800 watts for this alternator. This low-maintenance alternator is employed on two very different turbines. The original 134 gaiam real goods
    • low-Head stream engine installation SunShine to electricity Stream Engine uses a cast bronze Turgo-type inputs up to 140 volts, while feeding the batter- runner wheel. This Turgo wheel can handle a ies whatever it is that makes them happy. At the bit more water volume than the Harris pelton time of this writing, the Hydro MX60 isn’t ready wheel—up to about 200 gpm before it starts for release, but beta units are in trial. Please con- choking—and starts to deliver useful output sult with the Real Goods technical staff about at lower 15- to 20-foot head. Nozzles are cone- this or other transmission options. shaped plastic casings; you cut them at the size desired, from 1/8 inch up to 1 inch. Two- or four-nozzle turbines are available, with replace- Controllers A typical installation ment nozzles being a readily available bolt-in. Hydro generators require special controllers or The Low-Head Stream Engine uses the same regulators. Controllers designed for photovolta- places the batteries at alternator but is packaged quite differently. It ics may damage the hydro generator and will the house on top of the works on 2-10 feet of fall, which happens on very likely become crispy critters themselves if the downstream end of the turbine for a change. used with one. You can’t simply open the circuit hill, where the good Flows of 200-1,000 gpm can be accommodated when the batteries get full like you can with PV. view is, and the turbine through the 5-inch propeller turbine. The large So long as the generator is spinning, there needs draft tube on the output must be immersed in to be a place for the energy to go. Controllers for at the bottom of the the tail water. (See the illustration.) This turbine hydro systems take any power beyond what is hill, where the water requires more site preparation but almost no needed to keep the batteries charged and divert maintenance or attention once it’s installed and it to a secondary load, usually a water- or space- ends its maximum drop. tuned. heating element. So extra energy heats either Low-voltage power is domestic hot water or the house itself. These diversion controllers are also used with some difficult to transmit if Power Transmission wind generators and can be used for PV control large quantities or long One disadvantage of lower-voltage DC hydro as well if this is a hybrid system. systems is the difficulty of transmitting power distances are involved. from the turbine to the batteries, particularly with high-output sites. A typical installation Site Evaluation places the batteries at the house on top of the Okay, you have a fair amount of drop across hill, where the good view is, and the turbine at your property and/or enough water flow for the bottom of the hill, where the water ends its one of the low-head turbines, so you think mi- maximum drop. Low-voltage power is difficult cro-hydro is a definite possibility. What hap- to transmit if large quantities or long distances pens next? Time to go outside and take some are involved. The batteries should be as close measurements, then fill in the necessary in- to the turbine as is practical, but if there’s more formation on the Hydro Site Evaluation form. than 100 feet of distance involved, things will With the info on your completed form, the Real work better if the system voltage is 24 or even 48 Goods technicians can calculate which turbine volts. Transmission distances of more than 500 and options will best fill your needs, as well as feet often require expensive large-gauge wire what size pipe and wire and which balance-of- or technical tricks. Don Harris has been work- system components you require. Then we can ing with Outback Power Systems to develop a quote specific power output and system costs so hydroelectric version of their maximum power you can decide if hydro is worth the installation point tracking MX60 controller, which allows effort. solar living sourcebook 135
    • Stand the stick upright and mark it at eye lev- el. (Five feet even is a handy mark that simplifies the mathematics, if that’s close to eye level for SunShine to electricity you.) Measure and note the length of your stick from ground level to your mark. Starting at the turbine site, stand the stick upright, hold the carpenter’s level at your mark, make sure it is level, then sight across it uphill toward the water source. With hand motions and body English, guide your friend until the target is placed on the ground at the same level as your sightline, then have your friend wait for you to catch up. measuring fall Repeat the process, carefully keeping track of how many times you repeat. It is a good idea distanCe MeasuReMents to draw a map to remind you of landmarks and Keep the turbine and the batteries as close to- important details along the way. If you have a gether as practical. As discussed earlier, longer target and your friend has a stick (marked at the transmission distances will get expensive. The same height, please) and level, you can leapfrog more power you are trying to move, the more each other, which makes for a shorter party. important distance becomes. Multiply the number of repeats between the You’ll need to know the distance from the turbine site and the water source by the length proposed turbine site to the batteries (how many of your stick(s) and you have the vertical fall. feet of wire) and the distance from the turbine People actually get paid to have this much fun! site to the water collection point (how many feet of pipe). These distances are fairly easy to deter- Flow MeasuReMent mine; just pace them off or use a tape measure. Finally, you’ll need to know the flow rate. If you can, block the stream and use a length of pipe Fall (dRop oR Head) MeasuReMent to collect all the flow. Time how long it takes to Next, you’ll need to know the fall from the col- fill a 5-gallon bucket. Divide 5 gallons by your lection point to the turbine site. This measure- fill time in seconds. Multiply by 60 to get gal- ment is a little tougher. If there is a pipeline in lons per minute. Example: The 5-gallon bucket place already, or if you can run one temporarily takes 20 seconds to fill. So 5 divided by 20 = 0.25 and fill it with water, this part is easy. Simply in- times 60 = 15 gpm. If the flow is more than you stall a pressure gauge at the turbine site, make can dam up or get into a 4-inch pipe, or if the sure the pipe is full of water, and turn off the force of the water sweeps the bucket out of your water at the bottom. Read the static pressure hands, forget measuring: You’ve got plenty! Now you have all (which means no water movement in the pipe), the information needed and multiply your reading in pounds per square inch (psi) by 2.31 to obtain the drop in feet. If Conclusion to guesstimate how the water pipe method isn’t practical, you’ll have Now you have all the information needed to much electricity your to survey the drop or use a fairly accurate al- guesstimate how much electricity your pro- timeter or GPS device. A number of relatively posed hydro system will generate based on the proposed hydro system inexpensive sports watches come with a built-in manufacturer’s Output Charts on the next pag- will generate based altimeter now. If the altimeter can read ±10 feet, es. This will give you an indication of whether that’s close enough. Strap it on, take a hike, and or not your hydro site is worth developing, and on the manufacturer’s record the difference. if so, which turbine option is best. If you think Output Charts on the The following instructions represent the you have a real site, fill out the Real Goods Hy- classic method of surveying. You’ve seen survey dro Site Evaluation Form and send it to the next pages. parties doing this, and if you’ve always wanted Technical Department at Real Goods, or just to attend a survey party, this is your big chance give us a call. We will run your figures through to get in on the action. You’ll need a carpenter’s our computer sizing program, which allows us level (or a pocket sight level), a straight sturdy to size plumbing and wiring for the least power stick about eye-level tall, a brightly colored loss at the lowest cost, and a myriad of other cal- target that you’ll be able to see a few hundred culations necessary to design a working system. feet away, and a friend to carry the target and You’ll find an example of our Hydro Survey Re- to make the procedure go faster and more ac- port on the next page, followed by the form for curately. (It’s really hard to party alone.) the info we need from you. 136 gaiam real goods
    • HydRo suRVey saMple RepoRt CALCuLATION OF HyDrOELECTrIC POWEr POTENTIAL SunShine to electricity Copyright © 1988 by Ross Burkhardt. All rights reserved. EntEr Hydro SyStEm data HErE: Customer: meg a. Power Pipeline Length: 1,300 feet Pipe Diameter: 4 inches Available Water Flow: 100 gpm Vertical Fall: 200 feet Hydro to Battery Distance: 50 feet (one way) Transmission Wire Size: 2 AWG House Battery Voltage: 24 volts Hydro Generation Voltage: 29 volts Power produced at hydro: Power delivered to house: 49.78 amps 49.78 amps 29 volts 28.20 volts 1,443.53 watts 1,403.59 watts 4-nozzle, 24V, high-output with cooling turbine required Pipe Calculations Head Lost to Pipe Friction: 7.61 feet Pressure Lost to Pipe Friction: 3.29 psi Static Water Pressure: 86.62 psi Dynamic Water Pressure: 83.33 psi Static Head: 200.01 feet Dynamic Head: 192.40 feet Hydropower Calculations Operating Pressure: 83.33 psi Available Flow: 100 gpm Watts Produced: 1,443.53 watts Amperage Produced: 49.78 amps Amp-Hours per Day: 1,194.65 amp-hours Watt-Hours per Day: 34,644.83 watt-hours Watts per Year: 12,645,362.71 watt-hours Line Loss (using copper) Transmission Line One-Way Length: 50 feet Voltage: 29 volts Amperage: 49.78 amps Wire Size #: 2 AWG Voltage Drop: 0.8 volts Power Lost: 39.95 watts Transmission Efficiency: 97.23 percent Pelton Wheel rpm Will Be: 2,969.85 at optimum wheel efficiency This is an estimate only! Due to factors beyond our control (construction, installation, incorrect data, etc.), we cannot guarantee that your output will match this estimate. We have been conservative with the formulas used here, and most customers call to report more output than estimated. However, be forewarned! We’ve done our best to estimate conservatively and accurately, but there is no guarantee that your unit will actually produce as estimated. solar living sourcebook 137
    • real Goods SunShine to electricity Hydroelectric Site Evaluation Form Name: ______________________________________________________________ Address: ____________________________________________________________ ____________________________________________________________________ Phone: _______________________________________ Date: __________________ Pipe Length: ___________________ (from water intake to turbine site) Pipe Diameter: ____________________ (only if using existing pipe) Available Water Flow: ____________________ (in gallons per minute) Fall: _____________________ (from water intake to turbine site) Turbine to Battery Distance: _________________ (one way, in feet) Transmission Wire Size: _________________ (only if existing wire) House Battery Voltage: __________________ (12, 24, etc.) Alternate estimate (if you want to try different variables) Pipe Length: ___________________ (from water intake to turbine site) Pipe Diameter: ____________________ (only if using existing pipe) Available Water Flow: ____________________ (in gallons per minute) Fall: _____________________ (from water intake to turbine site) Turbine to Battery Distance: _________________ (one way, in feet) Transmission Wire Size: _________________ (only if existing wire) House Battery Voltage: __________________ (12, 24, etc.) For a complete computer printout of your hydroelectric potential, including sizing for wiring and piping, please fill in the above information and send it to Real Goods. 138 gaiam real goods
    • Wind Energy SunShine to electricity n This section was adapted from Wind Energy Basics, a real Southwest Windpower awakened latent con- goods solar living book by Paul gipe. He is also the author sumer interest in micro wind turbines with the of Wind Power: Renewable Energy for Home, Farm, and Busi- ness (2004). gipe has written and lectured extensively about introduction of its sleek Air series. Since launch- wind energy for more than two decades. ing the line in 1995, they’ve shipped thousands of the popular machines. “What Americans, and folks all over the Small Wind Turbines world, are finding out,” the Perezes say, “is that Come of Age wind power is an excellent and cost-effective al- ternative” to extending electric utility lines and The debut of micro wind turbines has revolu- fossil-fueled back-up generators. tionized living off the grid. These inexpensive machines have brought wind technology within reach of almost everyone. And their increasing Hybrid Wind and popularity has opened up new applications for wind energy previously considered off-limits, Solar Systems such as electric fence charging and powering re- You might say that joining wind and solar to- mote telephone call boxes, once the sole domain gether is a marriage made in heaven. The two of photovoltaics. resources are complementary: In many areas, wind is abundant in the winter when photo- annual average wind for voltaics are least productive, and sunshine is the united states. abundant in the summer when winds are often weakest. The Sun and wind together not only improve the reliability of an off-the-grid system, but also are more cost effective than using either source alone. Hybrid systems include a DC source center (for DC circuit breakers), batteries, inverters, and often an AC load center. These components are necessary whether you’re using just wind or Power class solar. So it’s best to spread the fixed cost of these 1 components over more kilowatt-hours by using 2 3 PV panels in addition to a wind turbine. 4 5 Engineers have found that these hybrids 6 7 perform even better when coupled with small back-up generators to reduce the battery stor- Micro wind turbines have been around for age needed. Many of those living off the grid decades for use on sailboats, but they gained reach the same conclusion by trial and error. prominence in the 1990s as their broader po- both wind and Pv can happily feed a common battery. tential for off-the-grid applications on land be- came more widely known. While micro wind turbines have yet to reach the status of widely available consumer commodities such as per- wind sonal computers, the day may not be far off. turbine The use of wind power is “exploding,” say Karen and Richard Perez, the editors of Home PV array = fuse Power magazine. “There are currently over 150,000 small-scale RE (renewable energy) sys- charge controller battery inverter tems in America and [the numbers] are grow- ing by 30% yearly. [But] [t]he small-scale use of battery wind power is growing at twice that amount— charger over 60% per year.” And a large part of that growth is due to Southwest Windpower of Flag- AC generators transfer AC load or utility switch center staff, Arizona. 144 gaiam real goods
    • Typically, a micro turbine, such as Southwest Generators Photo: © Paul Gipe Windpower’s Air series, or a small wind turbine, such as the Bergey XL1, a modest array of PV Most small wind turbines use permanent-mag- SunShine to electricity panels, batteries, and a small back-up generator net alternators. This is the simplest generator will suffice for most domestic uses. Though Pa- configuration and is nearly ideal for micro and cific Gas & Electric Co. found that most Califor- mini wind turbines. There is more diversity in nians living off the grid had back-up generators, household-size turbines, but again, nearly all use they seldom used them. In a well-designed hy- permanent-magnet alternators. Some manufac- brid system, the backup provides peace of mind turers use Ferrite magnets, others use rare-earth but little electricity. magnets. The latter have a higher flux density than ferrite magnets. Both types do the job. Size Matters poweR CuRVes In wind energy, size, especially rotor diameter, The power curve indicates how much power installing a 1,500-watt matters. Nothing tells you more about a wind tur- (in watts or kilowatts) a wind turbine’s genera- wind turbine on a tor will produce at any given wind speed. Power tilt-up tower using an bine’s potential than its diameter—the shorthand electric winch. for the area swept by the rotor. The wind turbine is presented on the vertical axis, wind speed on with the bigger rotor will intercept more of the the horizontal axis. In the advertising wars be- wind stream and will almost invariably generate tween wind turbine manufacturers, often the more electricity than a turbine with a smaller ro- focus is the point at which the wind turbine tor, regardless of their generator ratings. reaches its “rated,” or nominal, power. Though The area swept by a wind turbine rotor is rated power is just one point on a wind turbine’s equivalent to the surface area of a photovoltaic power curve, many consumers mistakenly rely array. When you need more power in a PV ar- on it when comparison shopping. But not all ray, you increase the surface area of the panels power curves are created equal. Some power exposed to the Sun by adding more panels. In curves are, to be diplomatic, more “aggressive” the case of wind, you find a wind turbine that than others. sweeps more area of the wind—a turbine with a Manufacturers may pick any speed they greater rotor diameter. choose to “rate” their turbine. In the 1970s, it Micro turbines range in size from 3 to 5 feet was easy for unscrupulous manufacturers to in diameter. The lower end of the range is repre- manipulate this system to make it appear that sented by the Southwest Windpower’s Air series. their turbines were a better buy than competing These machines are suitable for recreational ve- products. By pushing “rated power” higher, they Photo: © Paul Gipe hicles, sailboats, fence charging, and other low- were able to show lower relative costs (turbine power uses. Micro turbines will generate about cost/rated power) or they were able to increase 300 kilowatt-hours (kWh) per year at sites with their price—and profits—proportionally. average wind speeds typical of the Great Plains Unlike wind farm turbines, the performance (about 12 mph at the height of the turbine). of many small wind turbines has not been tested Mini wind turbines are slightly larger than to international standards. As a rule, don’t place micro turbines and are well suited for vacation much faith in power curves, unless the manu- cabins. They span the range from 5 to 9 feet in facturer has clearly stated the conditions under diameter and include Southwest Windpower’s which the curve was measured (usually in a de- Whisper 200 as well as the Bergey Windpower tailed footnote), or in “rated power.” Some pow- XL1. Wind turbines in this class can produce er curves can be off by 40% in low winds and 1,000-2,000kWh per year at sites with an aver- as much as 20% at “rated” power. And it’s the age annual wind speed of 12 mph. performance in lower winds that matters most. bob and ginger morgan’s bergey excel Household-size turbines, as the name im- Most homeowners seldom see their turbines being installed by a plies, are suitable for homes, farms, ranches, operating in winds at “rated” speeds of, say, 28 crane near Tehachapi, small businesses, and telecommunications. mph. Small wind turbines operate most of the california. They span an even broader range than the other time in winds at much lower speeds, often from © Paul gipe size classes and encompass turbines from 10 to 10 to 20 mph. For size or price comparisons, 23 feet in diameter. This class includes Bergey’s stick with rotor diameter or swept area. Both are Excel model and African Windpower’s 3.6 me- more reliable indicators of performance than ter- (12-foot-) diameter turbine. Household- power curves are. size wind turbines can generate from 2,000kWh to 20,000kWh per year at 12-mph sites. solar living sourcebook 145
    • robustness swept by the rotor. By this criteria, a turbine that has a relative mass of 10kg/m2 may be more ro- Wind turbines work in a far more rugged envi- bust—and rugged—than a turbine with a spe- SunShine to electricity ronment than photovoltaic panels that sit qui- cific mass of 5kg/m2. etly on your roof. You quickly appreciate this when you watch a small wind turbine strug- gling through a gale. There’s no foolproof way Siting to evaluate the robustness of small wind turbine To get the most out of your investment, site your designs. wind turbine to best advantage: well away from In general, heavier small wind turbines have buildings, trees, and other wind obstructions. proven more rugged and dependable than Install the turbine on as tall a tower as you’re lightweight machines. Wisconsin’s wind guru comfortable working with. Jason Edworthy’s Mick Sagrillo is a proponent of what he calls experience at NorEnergy Systems in Canada The sleek air 403 the “heavy metal school” of small wind turbine convinces him that the old 30-foot rule still ap- industrial Turbine design. Heavier, more massive turbines, he says, plies. This classic rule from the 1930s dictates typically last longer. Heavier in this sense is the that for best performance, your wind turbine weight or mass of the turbine relative to the area should be at least 30 feet above any obstruction Small Wind Turbines, note that there are 5,400 turbines on this site. That gives an average of 3. Curry & Kerlinger, “Those statis- tics were cited in reports published Cuisinart for birds or 0.19 bird kills per turbine per year9. by the National Institute for Urban Wildlife and U.S. Fish and Wildlife red herring? The problem seems to be the abun- Service.” www.currykerlinger dance of prey in the tall grasses A vian mortality is an issue that always seems to come up with wind turbines. Do birds die from around the towers, and the fact that this is a heavily used migratory .com/birds.htm. 4. Defenders of Wildlife, “Bird mor- tality from wind turbines should route and early tower designs pro- be put into perspective.” www. running into wind turbine blades, vided a wealth of good perches. defenders.org/habitat/renew/wind towers, and guy wires? Yes, they do. That’s the true story for large .html. In large numbers? Hardly. Let’s look power-production turbines. Bird 5. Curry & Kerlinger, “U.S. Fish and at the facts. Birds die all the time, kills are a nonissue. In comparison, Wildlife Service estimates that bird in great numbers, due to human collisions with tall, lighted com- residential-size turbines and towers endeavors. The number-one bird munications towers, and their guy simply do not pose any significant killer is glass-faced office buildings. wires result in 4 to 10 million bird risk to birds. The towers are too These account for 100 million to deaths a year.” www.currykerlinger short, and the blade swept area 900 million bird deaths per year1, 2. .com/birds.htm. is too small. The chance of your Some skyscrapers have been moni- 6. Curry & Kerlinger, “The National residential turbine ever hitting a Audubon Society says 100 million tored and shown to kill as many as bird are vanishingly small. If you or birds a year fall prey to cats.” www 200 birds per day. Cars and trucks your neighbors are truly concerned .currykerlinger.com/birds.htm. kill another 50 to 100 million birds about bird deaths, getting rid of 7. Defenders of Wildlife, the Ameri- per year3, 4. Cell phone, TV, radio, Muffy would have much more can Bird Conservancy estimates and other communications towers real effect. that feral and domestic outdoor kill 4 million to 10 million birds per cats probably kill on the order —Doug Pratt year5. And finally, Muffy the house- of hundreds of millions of birds cat and all her friends take at least 1. Curry & Kerlinger, Dr. Daniel per year (Case 2000). One study 100 million birds a year, possibly Klem of Muhlenberg College has estimated that in Wisconsin alone, many more6, 7. done studies over a period of 20 annual bird kill by rural cats might In comparison, the vast major- years, looking at bird collisions range from 7.8 million to 217 with windows. www.currykerlinger million birds per year (Colemen & ity of large wind plants report zero .com/birds.htm. Temple, 1995). www.defenders bird kills8, and even the famous 2. Defenders of Wildlife, “Bird mor- Altamont Pass area, in which wind .org/habitat/renew/wind.html. tality from wind turbines should 8. www.currykerlinger.com/studies. turbine bird kills were first report- be put into perspective.” www. htm ed, has about 1,000 bird deaths per defenders.org/habitat/renew/wind 9. www.nrel.gov/docs/fy04osti/33829 year. This sounds like a lot, until we .html. .pdf 146 gaiam real goods
    • ing and you’re comfortable with the technology, you can try your hand with a larger turbine. SunShine to electricity Typical Costs The cost of a wind system includes the cost of the turbine, tower, ancillary equipment (dis- connect switches, cabling, etc.), and installa- tion. The total cost of a micro turbine can be as little as $1,000, depending upon the tower used and its height, while that of a household-size Increase in power with height above 30 ft (10m). machine can exceed $50,000. When comparing prices, remember that bigger turbines cost more chart adapted from Wind Power for Home & Business. but often are more cost effective. For an off-the- grid power system, the addition of a wind tur- within 200 feet of the tower. Under the best of bine will almost always make economic sense conditions, a tower height of 30 feet is the abso- by reducing the number of photovoltaic panels lute minimum, says Edworthy. or batteries needed. Putting a turbine on the roof is no alter- For grid-intertie systems, the economics de- native. Seldom can you get the turbine high pend upon the winds at your site and a host of enough to clear the turbulence caused by the other factors, including the average wind speed, building itself. Imagine trying to mount a 30- the cost of the wind system, the cost of utility foot-tall tower on a steeply pitched roof—it’s a power, and whether your utility provides net recipe for disaster. Even if you could, turbine- billing. induced vibrations will quickly convince you otherwise. (It’s like putting a noisy lawn mower on your roof.) While many small wind turbines Some Do’s and Don’ts are relatively quiet, some are not—another good Do plenty of research. It can save a lot of The bergey excel trouble—and expense—later. Turbine reason to put them out in the open, well away from buildings. Do visit the library. Books remain amazing repositories of information. (We do have a bias about books, since we write them. But we’ve al- Towers ways firmly believed that “you get what you pay Most small wind turbines are installed on guyed, for” when it comes to free information, whether tubular masts that are hinged at the base. With it’s from the Internet, manufacturers, or their an accompanying gin pole, these towers can be trade associations.) raised and lowered, simplifying installation and Do talk to others who use wind energy. service. Some tilt-up towers use thin-walled They’ve been there. You can learn from them steel tubing, others use thick-walled steel pipe. what they did right and what they’d never do Household-size turbines also use guyed masts again. of steel lattice as well as freestanding truss tow- Do read and, equally important, follow di- ers. With the advent of pre-engineered tubular rections. mast kits, there’s now less excuse than ever for Do ask for help when you’re not sure about installing micro and mini wind turbines on in- something. The folks at Real Goods Renewables adequate towers. are there to help. installation Those with good tool skills—who work safely— eStimateD annual enerGy output can install a micro turbine themselves using a at hub height in thousand kWh/y pre-engineered tilt-up tower kit. Installing mini Avg Rotor Diameter, m (ft.) wind turbines, because of the greater forces in- Wind 1 1.5 3 7 18 40 volved, requires considerably more skill. House- speed (3.3) (4.9) (9.8) (23) (60) (130) hold-size turbines should be left only to profes- (mph) thousands of kWh per year sionals—and even the pros have made tragic 9 0.15 0.33 1.3 7 40 210 mistakes. If you like doing the work yourself, 10 0.20 0.45 1.8 10 60 290 start with a micro turbine and a tilt-up tower. 11 0.24 0.54 2.2 13 90 450 Once you’re satisfied you know what you’re do- solar living sourcebook 147
    • Do build to code. In the end, it makes for a Photo: © Paul Gipe tidier, safer, and easier-to-service system. Do take your time. Remember, there’s no SunShine to electricity rush. The wind will always be there. Do be careful. Small wind turbines may look harmless, but they’re not. Don’t skimp and don’t cut corners. Tak- ing shortcuts is always a surefire way to ruin an otherwise good installation. Don’t design your own tower—unless you’re a licensed professional engineer. Don’t install your turbine on the roof despite what some manufacturers may say! And, of course, don’t believe everything you read in sales brochures. In general, doing it right the first time may Photo: © Paul Gipe take longer and cost slightly more, but you’ll be a lot happier in the long run. n n souRCes oF inFoRMation For more on micro turbines, see Wind Energy Basics (Chelsea Green Publishing, 1999), avail- able from Real Goods (see page 533). It fully describes the new class of small wind turbines, dubbed micro turbines. These inexpensive ma- real goods solar living center’s Whisper 3000 wind chines, when coupled with readily available turbine atop a hinged, tilt-up tower in Hopland, california. photovoltaic panels, have revolutionized living off the grid. plains of northern Europe in the 1990s. Selected bergey excel and photovoltaic panels For more on small wind turbine technology, as one of the outstanding academic books pub- at the home of dave see Wind Power: Renewable Energy for Home, lished in 1995. bittersdorf, founder of Farm, and Business (Chelsea Green Publishing, To determine your local wind resources, visit nrg systems. 1993), also available from Real Goods (see page http://rredc.nrel.gov/wind/pubs/atlas/ or search 534). This book explains how modern, inte- for the National Renewable Energy Laborato- grated wind turbines work and how to use them ry’s Wind Energy Resource Atlas of the United most effectively. States. For information about the commercial wind For tips on installing micro and mini wind power industry, see Wind Energy Comes of Age turbines using a Griphoist-brand winch, see (John Wiley & Sons, 1995), a chronicle of wind “Get a Grip!” in Homepower Magazine #68 (De- energy’s progress from its rebirth during the cember 1998/January 1999), or visit www.wind- oil crises of the 1970s to its maturation on the works.org. 148 gaiam real goods
    • The Gipe Family Do-It-yourself Wind Generator Slide Show SunShine to electricity All photos: © Paul Gipe 1. Taking delivery of a new 2. checking the packing 3. securing the tower’s 4. aligning the guy 5. driving the screw air turbine and 45-foot list against parts delivered. base plate. anchors. anchors. tower. 7. assembling the mast. 8. clevis and gated fitting 6. unspooling the guy hook. 9. gin pole and lifting 10. strain relief for cable. cables. supporting power cables. 13. slowly raising the turbine with a griphoist-brand hand winch. 11. Final assembly of the 12. disconnect switch and turbine. junction box. 14. air turbine safely installed with a griphoist- brand hand winch. solar living sourcebook 149
    • Hydrogen Fuel Cells SunShine to electricity Power Source of Our Bright industrialization of the world is requiring more and more fuel, creating our current unsustain- and Shining Future? able run on the world’s energy reserves. The ul- Fuel cells seem to be the darlings of the energy timate effect of all this fossil fuel burning is to world lately. If we believe all the hype, they’ll create global climate change and global warm- bring clean, quiet, reliable, cheap energy to the ing. Most scientists predict that if we fail to curb masses, allowing us to continue an energy-in- our fossil fuel consumption, the average world tensive lifestyle with no penalties or roadblocks. temperature will rise 7-18 degrees Fahrenheit Are fuel cells going to save our energy-hog (4-10 degrees Celsius) in the next 50-100 years, butts? Maybe. They sure will help. Can you and the oceans will rise 3-8 feet in the same time. buy one yet? Certainly . . . for a price. It helps Other, even less savory results of global warm- if you’re the Department of Defense or have a ing are still speculative and debatable. What fat government grant or contract in your back is known is that we’re messing with things we pocket. This is still a very young, very rapidly don’t understand, can’t fix quickly, and almost developing technology. The first small commer- surely won’t enjoy. For a sobering perspective, cial units started appearing in 2003 for relatively feel free to review Climate Change and the Need outrageous prices. Residential units that will to Eliminate Fossil Fuels in Chapter 1. run off natural gas or propane to provide back- Fuel cells are chemical devices that go from a up power probably won’t show up until at least source, like hydrogen or natural gas, straight to 2010, and they’re liable to be fairly expensive. heat and electrical output, without the combus- Want a bit more background info before you or- tion step in the middle. Fuel cells increase ef- der one? Good plan, read on. ficiency by two- or three-fold and dramatically Traditional energy production, for either reduce the unintended byproducts. A fuel cell is electricity or heat, depends on burning a fuel an electrochemical device, similar to a battery, source like gasoline, fuel oil, natural gas, or coal except fuel cells operate like a continuous bat- to either spin an internal combustion engine or tery that never needs recharging. So long as fuel to heat water, then piping the resulting steam or is supplied to the negative electrode (anode) hot water to warm our buildings or run the tur- and oxygen, or free air, is supplied to the posi- bines to make electricity. Burning fuels produce tive electrode (cathode), they will provide con- some byproducts we’d be better off not letting tinuous electrical power and heat. Fuel cells can loose into the environment, and every energy reach 80% efficiency when both the heat and conversion costs some efficiency. The increasing electric power outputs are utilized. 162 gaiam real goods
    • How Fuel Cells opeRate tors, and methanol and even gasoline have been A fuel cell is composed of two electrodes sand- used in experimental automotive fuel cells. But if you feed the fuel cell something other than SunShine to electricity wiched around an electrolyte material. Hydro- gen fuel is fed into the anode. Oxygen (or free pure hydrogen, you’re going to get something air) is fed into the cathode. Encouraged by a more than pure water in the output, carbon catalyst, the hydrogen atom splits into a pro- dioxide usually being the biggest component. ton and an electron. The proton passes through Fuel cells emit 40%-60% less carbon dioxide the electrolyte to reach the cathode. The elec- than conventional power generation systems tron takes a separate, outside path to reach the using the same hydrocarbon fuel. Other air pol- cathode. Since electrons flowing through a wire lutants such as sulfur oxides, nitrogen oxides, is commonly known as “electricity,” we’ll make carbon monoxide, and unburned hydrocarbons those free electrons do some work for us on the are nearly absent, although you’ll still get some way. At the cathode, the electrons, protons, and trace byproducts we’d be better off without. oxygen all meet, react, and form water. Fuel cells The dream is to build a fuel cell that accepts are actually built up in “stacks” with multiple water input. But it takes more energy to split the layers of electrodes and electrolyte. Depending water into hydrogen and oxygen than we’ll get on the cell type, electrolyte material may be ei- back from the fuel cell. One potential future sce- ther liquid or solid. nario has large banks of PV cells splitting water. Like other electrochemical devices such as The hydrogen is collected and used to run cars batteries, fuel cells eventually wear out and the and light trucks. Efficiency isn’t great, but nasty stacks have to be replaced. Stack replacement byproducts are zero. cost is typically 20%-25% of the initial fuel cell cost. Current designs have run times of 40,000- 60,000 hours. Under continuous operation that’s Competing Technologies 4.5-6.8 years. Just as there’s more than one “right” chemistry with which to build a battery, there are quite wHat’s “Fuel” to a Fuel Cell? a number of ways to put together a functional In purest form, a fuel cell takes hydrogen, the fuel cell. As an emerging technology, several most abundant element in the universe, and fuel cell chemical combinations are receiving combines it with oxygen. The output is electric- experimental interest, substantial funding, and ity, pure water (H2O), and a bit of heat. Period. absolutely furious development. At the risk of Very clean technology! No nasty byproducts and boring you, or scaring you all away, we’re going no waste products left over. There are some real to list the major chemical contenders for fuel obvious advantages to using the most abundant cell power and their strong or weak points. element in the universe. We’ve got plenty of it pHospHoRiC aCid The typical on hand, and as most anyone can clearly see, a hydrogen-based economy is far more clean and This is the most mature fuel cell technology. phosphoric acid fuel cell is about the size of sustainable than a petroleum-based economy. Quite a number of 200-kilowatt demonstration/ a freight car. This one’s On the downside, hydrogen doesn’t usually experimental units are in everyday operation at in new York’s central exist in pure form on Earth. It’s bound up with hospitals, nursing homes, hotels, schools, office Park. oxygen to make water, or with other fuels like natural gas or petroleum. If you run down to your friendly local gas supply to buy a tank of hydrogen, what you get will be a byproduct of petroleum refining. Since hydrogen probably isn’t going to be supplied in pure form, most commercial fuel cells have a fuel-processing component as part of the package. Fuel processors, or “reformers,” do a bit of chemical reformulation to boost the hydrogen content of the fuel. This makes a fuel cell that can run on any hydrocarbon fuel. Hy- drocarbon fuels include natural gas, propane, gasoline, fuel oils, diesel oil, methane, ethanol, methanol, and a number of others. Natural gas and propane are favored for stationary genera- solar living sourcebook 163
    • buildings, and utility power plants. The Depart- room temperature, so start-up time is minimal. ment of Defense currently runs about 30 of Stack life expectancy is about 40,000 hours. these with 150- to 250-kilowatt output. If you A few small demonstration PEM fuel cells SunShine to electricity simply must have a fuel cell in your life right are available for sale currently, but for some- now, this is your baby. They are available for thing that’s going to run your house, you’ll sale . . . for a price. Currently that price is about need some patience. A great many manufactur- $3,000 per kilowatt. These are large, stationary ers have residential units under development, power plants, usually running on natural gas. and many are in beta testing; and if you want Phosphoric acid cells do not lend themselves it bad enough, you can find one, although this well to small-scale generators. Locomotives and technology isn’t expected to fully mature till buses are probably about as small as they will go. sometime after 2010. For current information, Operating temperatures are 375°-400°F, so they visit the nonprofit Fuel Cells 2000 Web site at need thermal shielding. Efficiency for electric www.fuelcells.org. production alone is about 37%; if you can utilize both heat and power, efficiency hits about 73%. Molten CaRBonate and solid oxide Stack life expectancy is about 60,000 hours. These two fuel cell technologies aren’t related, except that they are both large base-load type pRoton exCHanGe MeMBRane cells that utility companies can use to supply PEM is the fuel cell technology that is prob- grid power. These technologies have barely ably seeing the most intense development and delivered their first prototypes, so operational is the type of fuel cell you are most likely to see plants are still far in the future. Very high op- in your lifetime. Because it offers more power erating temperatures, 1,200°-1,800°F, are the output from a smaller package, low operating norm for these cells. Electrical generation effi- temperatures, and fast output response, this is ciencies are over 50%, and pollution output is the favored cell technology for automotive and way, way down, so these technologies are going residential power use. Thanks to their low noise to be very attractive to utility companies. The level, low weight, quick start-up, and simple sup- high operating temperatures mean that these port systems, experimental PEM fuel cells have cells don’t turn on or off casually. Start-up can even been produced for cell phones and video take over 10 hours. These aren’t fuel cells for off- cameras. Recent advances in performance and the-grid homes. design raise the tantalizing promise of the low- est cost of any fuel cell system. Current prices are about $3,000 per kilowatt, but they will drop Cruisin’ the City on as mass-production economies begin to kick Fuel Cells? in. Operating temperature is a very low 175°- One of civilization’s biggest fossil fuel uses, and 200°F, so minimal thermal shielding is needed. the one we seem to have the hardest time wean- Efficiency for electric production alone is about ing ourselves from, is automobiles. Do fuel cells 36%, and if you can utilize both heat and power, offer any hope for hopeless driving addicts? efficiency hits about 70%. PEM cells can start Yes, they do. Every major auto manufacturer delivering up to 50% of their rated power at has a well-funded, active fuel cell development program. Several manufacturers, Daimler- Chrysler, Toyota, and Honda, in particular, Pem cells are have several generations of prototypes behind smaller, run at lower them already. The stakes are high. The company temperatures, and that develops a workable fuel cell-powered auto are more consumer holds the keys to the future. Several manufac- friendly. turers are aiming to make the first commercial models to be available. These will probably be methanol-fueled PEM cells with a modest bat- tery or capacitor pack to help meet sudden ac- celeration surges. One of the primary problems has been the size of the fuel cell stack required. Mercedes’ first prototype was a small bus; its second pro- totype was a van; and its latest, fifth prototype is in the new compact A-series sedan. Each 164 gaiam real goods
    • prototype has room for just a driver and passen- The mazda Premacy ger. So cell stacks are getting smaller and more Fc-ev, a protorype of a fuel cell car. efficient, but we could still stand some improve- SunShine to electricity ment (or an expectation adjustment). Crash-safe hydrogen storage in a vehicle also continues to be a trying problem. We demand much safer vehicles than we used to. The first generations of fuel cell vehicles will be using on- board reformers with methanol or other liquid fuels, so this isn’t a problem that requires an im- mediate solution. All in all, we’re skeptical about the near-term use free, renewable energy sources. No matter potential of hydrogen fuel cells to reduce green- how much you extract today, it doesn’t impact house gas emissions in the transportation sec- how much you can extract tomorrow, the next tor. For the foreseeable future, hybrid electric day, and so on. This is the major difference be- and biofuel-powered vehicles are a much better, tween technologies that harvest renewable en- more realistic bet. You’ll find a fuller explana- ergy, and fuel cells, which are primarily going to tion of this subject in Chapter 12, “Sustainable continue using nonrenewable energy sources. Transportation.” In the long run, we think that fast-starting PEM fuel cells will take the place of back-up How Do Fuel Cells Compare generators in residential energy systems. They’ll be in place to pick up the occasional shortfall with Solar or Wind Energy? in renewable-powered off-the-grid systems or As an electrical supplier, a fuel cell is closer kin to provide back-up AC power for grid-supplied to an internal combustion engine than to any homes when the utility fails. If your home is off renewable energy source. Think of a fuel cell as the grid, then solar, wind, or hydro is still go- a vastly improved generator. It burns less fuel, it ing to be the most cost-effective and environ- makes less pollution, there are no moving parts, mentally responsible primary power source. and it makes hardly any noise. But unless you In an ideal world, every back-up power fuel have a free supply of hydrogen, it will still use cell would be supplied by a small PV-powered nonrenewable fossil fuels for power, which will hydrogen extractor that cracks water all day cost something. and stores the resulting hydrogen for later use. Photovoltaic modules, wind generators, hy- Guess we’d better get busy designing renewable dro generators, and solar hot-water panels all energy-powered hydrogen extractors. solar living sourcebook 165