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DOE/GO-102001-1102 FS175 March 2001 EFFICIENCY : AND

RCLEARINGHOUS ENEWABLE An Overview ENERGY What is Renewable Energy? safety concerns and waste disposal prob- lems, the will retire much of Renewable energy uses energy sources its nuclear capacity by 2020. In the mean- that are continually replenished by time, the nation’s energy needs are —the , the , water, the expected to grow by 33 percent during the Earth’s , and plants. Renewable next 20 years. Renewable energy can help energy technologies turn these into fill the gap. usable forms of energy—most often elec- tricity, but also heat, chemicals, or Even if we had an unlimited supply of fos- mechanical . sil fuels, using renewable energy is better for the environment. We often call renew- Why Use Renewable Energy? able energy technologies “clean” or Today we primarily use fossil fuels to heat “green” because they produce few if any and power our homes and our cars. pollutants. Burning fossil fuels, however, It’s convenient to use , oil, and natural sends gases into the atmos- gas for meeting our energy needs, but we phere, trapping the sun’s heat and con- have a limited supply of these fuels on the tributing to global warming. Earth. We’re using them much more scientists generally agree that the Earth’s rapidly than they are being created. Even- average has risen in the past tually, they will run out. And because of century. If this trend continues, sea levels will rise, and scientists predict that floods, heat waves, , and other extreme weather conditions

E could occur more often.

Other pollutants are released into the air, soil, and water when fossil fuels are burned. These pollutants take a dramatic toll on the environment—and on humans. Air contributes to diseases like asthma. Acid from sulfur dioxide and nitrogen oxides harms plants and fish. Nitrogen oxides also National Park Service, NREL/PIX04924 contribute to smog. A PV-system at the Pinnacles National Monument in eliminates a $20,000 annual fuel bill for a diesel generator that pro- duced each year 143 tons of —a .

NT O E F E TM N R E A R This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. The P G

E Y D document was produced by the Information and Outreach Program at NREL for the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency

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A N and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on C I I T R E information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC. D E M ST A ATES OF Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste Renewable energy will also help us develop and secu- rity. The United States imports more than Bioenergy is the energy derived from bio- 50 percent of its oil, up from 34 percent in (organic matter), such as plants. If 1973. Replacing some of our you’ve ever burned wood in a fireplace or with fuels made from plant matter, for campfire, you’ve used bioenergy. But we example, could save money and don’t get all of our resources strengthen our . directly from trees or other plants. Many industries, such as those involved in con- Renewable energy is plentiful, and the struction or the processing of agricultural is our technologies are improving all the time. products, can create large quantities of There are many ways to use renewable unused or residual biomass, which can most mature and energy. Most of us already use renewable serve as a bioenergy source. energy in our daily lives. largest source of Biopower Hydropower After hydropower, biomass is this coun- renewable power… try’s second-leading resource of renewable Hydropower is our most mature and energy, accounting for more than 7,000 largest source of renewable power, pro- MW of installed capacity. Some utilities ducing about 10 percent of the nation’s and power generating companies with . Existing hydropower capacity coal power plants have found that replac- is about 77,000 megawatts (MW). Hydro- ing some coal with biomass is a low-cost power plants convert the energy in flowing option to reduce undesirable emissions. water into electricity. The most common As much as 15 percent of the coal may be form of hydropower uses a on a river replaced with biomass. Biomass has less to retain a large of water. Water is sulfur than coal. Therefore, less sulfur released through turbines to generate dioxide, which contributes to acid rain, is power. “Run of the river” systems, how- released into the air. Additionally, using ever, divert water from the river and biomass in these boilers reduces nitrous direct it through a pipeline to a turbine. oxide emissions.

Hydropower plants produce no air emis- A process called —the conver- sions but can affect water quality and sion of biomass into gas, which is burned wildlife habitats. Therefore, hydropower in a gas turbine—is another way to gener- plants are now being designed and oper- ate electricity. The decay of biomass in ated to minimize impacts on the river. landfills also produces gas, mostly Some of them are diverting a portion of , which can be burned in a boiler the flow around their to mimic the to produce steam for natural flow of the river. But while this or industrial processes. Biomass can also improves the be heated in the absence of oxygen to wildlife’s river chemically convert it into a type of fuel oil, habitat, it also called pyrolysis oil. Pyrolysis oil can be reduces the power used for power generation and as a feed- plant’s output. In stock for fuels and chemical production. addition, fish lad- ders and other approaches, such Biomass can be converted directly into liq- as improved tur- uid fuels, called biofuels. Because biofuels bines, are being are easy to and possess high used to assist fish energy density, they are favored to fuel with migration vehicles and sometimes stationary power and lower the generation. The most common is number of fish , an made from the fermen- killed. tation of biomass high in . Duane Hippe, NREL/PIX04410 The current largest source of ethanol is corn. A small-scale hydropower system in King Cove, Some cities use ethanol as a addi- Alaska, provides residents in this remote area with a less expensive source of electricity. tive to help meet air quality standards for

2 ozone. Flex-fuel amounts to 50,000 times the energy of all vehicles are also oil and gas resources in the world. In the now on the market, United States, most geothermal which can use a are located in the western states, Alaska, mixture of gasoline and Hawaii. GHPs, however, can be used and ethanol, such almost anywhere. as E85—a mixture of 85 percent Geothermal Electricity Production ethanol and 15 per- plants access the under- cent gasoline. ground steam or hot water from wells Another biofuel is drilled a mile or more into the earth. The , which steam or hot water is piped up from the can be made from well to drive a conventional steam turbine,

Warren Gretz, NREL/PIX04744 Gretz, Warren vegetable and ani- which powers an . Typi- This gasifier in Burlinton, Vermont, converts biomass mal fats. Biodiesel cally, the water is then returned to the into a clean gas for electricity production can be used to fuel ground to recharge the reservoir and com- a vehicle or as a plete the renewable energy cycle. fuel additive to reduce emissions. There are three types of geothermal power Corn ethanol and biodiesel provide about plants: dry steam, flash steam, and binary 0.4 percent of the total liquid fuels market. cycle. Dry steam plants draw from reser- To increase our available supply of biofu- voirs of steam, while both flash steam and els, researchers are testing crop residues— binary cycle plants draw from reservoirs such as cornstalks and leaves—wood of hot water. Flash steam plants typically chips, food waste, grass, and even trash as use water at greater than potential biofuel sources. 360°F. Unlike both steam and flash plants, binary-cycle plants transfer heat from the Biobased Products water to what’s called a working fluid. If you’ve ever burned Biomass—corn, , , wood, Therefore binary cycle plants can operate and residues—can also be used to produce using water at lower temperatures of wood in a fireplace chemicals and materials that we normally about 225° to 360°F. obtain from petroleum. Industry has or campfire, you've already begun to use cornstarch to pro- duce commodity plastics, such as used bioenergy. shrinkwrap, plastic eating utensils, and even car bumpers. Commercial develop- ment is underway to make thermoset plastics, like electrical plate covers, from wood residues.

Geothermal Energy

The Earth’s core, 4,000 miles below the sur- INEEL, NREL/PIX07658 Joel Renner, face, can reach temperatures of 9000° F. The Steamboat Hills geothermal power plant This heat——flows out- in Steamboat Springs, Nevada has an electric- ity generation capacity of 13.5 MW. ward from the core, heating the surround- ing area, which can form underground reservoirs of hot water and steam. These All of the U.S. geothermal power plants reservoirs can be tapped for a variety of are in California, Nevada, Utah, and uses, such as to generate electricity or heat Hawaii. Altogether about 2800 MW of buildings. By using geothermal heat geothermal electric capacity is produced pumps (GHPs), we can even take advan- annually in this country. tage of the shallow ground’s stable tem- perature for heating and cooling buildings. Geothermal Direct Use If you’ve ever soaked in a natural , The geothermal energy potential in the you’re one of millions of people around the uppermost 6 miles of the Earth’s crust world who has enjoyed the direct use of

3 geothermal energy. Direct-use applications require geothermal temperatures between about 70° to 302°F—lower than those Solar technologies tap directly into the required for electricity generation. The infinite power of the sun and use that United States already has about 1,300 geot- energy to produce heat, , and power. hermal direct-use systems in operation. Passive Solar and Heating Altogether about In a direct-use system, a well is drilled People have used the sun to heat and light into a geothermal reservoir, which pro- their homes for centuries. Ancient Native 2800 MW of vides a steady stream of hot water. Some Americans built their dwellings directly systems use the water directly, but most into south-facing cliff walls because they geothermal electric pump the water through what’s called a knew the sun travels low across the south- heat exchanger. The heat exchanger keeps ern sky in the Northern Hemisphere dur- capacity is produced the water separate from a working fluid ing the winter. They also knew the (usually water or a mixture of water and massive rock of the cliff would absorb annually in this antifreeze), which is heated by the geot- heat in winter and protect against wind hermal water. The working fluid then and snow. At the same time, the cliff- country. flows through piping, distributing the dwelling design blocked during heat directly for its intended use. the summer, when the sun is higher in the sky, keeping their dwellings cool. The heated water or fluid can be used in a building to replace the traditional heat The modern version of this sun-welcoming source—often —of a boiler, fur- design is called passive solar because no nace, and hot water heater. Some cities pumps, fans, or other mechanical devices and towns actually have large direct-use are used. Its most basic features include heating systems—called — large, south-facing windows that fill the that provide many buildings with heat. home with natural sunlight, and dark tile Geothermal direct use is also used in agri- or brick floors that store the sun’s heat and culture—such as for fish farms and to heat release it back into the home at night. In the —and for industrial food pro- summer, when the sun is higher in the sky, cessing (vegetable dehydration). window overhangs block direct sunlight, which keeps the house cool. Tile and brick Geothermal Heat Pumps floors also remain cool during the summer. While air temperatures can vary widely through the seasons, the temperatures of Passive solar design combined with the shallow ground only range from 50° to energy efficiency will go even further. 70°F depending on latitude. GHPs draw Energy-efficient features such as energy- on this relatively stable temperature as a saving windows and appliances, along source for heating buildings in the winter with good insulation and weatherstrip- and keeping them cool in the summer. ping, can make a huge difference in energy and cost savings. Through underground piping, a GHP dis- charges heat from inside a building into Solar the ground in the summer, much like a Solar energy can be used to heat water for refrigerator uses electricity to keep its inte- your home or your swimming pool. Most rior cool while releasing heat into your solar water-heating systems consist of a

Warren Gretz, NREL/PIX06537 Gretz, Warren kitchen. In the winter, this process is solar collector and a water storage tank. This homeowner in Aurora, reversed; the GHP extracts heat from the Colorado, uses a GHP to heat ground and releases it into a building. Solar water-heating systems use collectors, and cool his home. generally mounted on a south-facing roof, Because GHPs actually move heat between to heat either water or a heat-transfer homes and the earth, instead of burning fluid, such as a nontoxic antifreeze. The fuels, they operate very cleanly and effi- heated water is then stored in a water tank ciently. In fact, GHPs are at least three times similar to one used in a conventional gas more efficient than even the most energy- or electric water-heating system. efficient furnaces on the market today.

4 There are basically systems are now combined with a small three types of solar solar-electric panel to power the pump. collectors for heat- ing water: flat- The amount of hot water a solar water plate, evacuated- heater produces depends on the type and tube, and concen- size of the system, the amount of sun trating. The most available at the site, proper installation, common type, a and the tilt angle and orientation of the flat-plate collector, is collectors. But if you’re currently using an an insulated, electric water heater, is weatherproof box a cost-effective alternative. If you own a containing a dark swimming pool, heating the water with absorber plate solar collectors can also save you money.

Andrew Gordon and Fox & Fowle Architects, NREL/PIX09052 and Fox & Fowle Architects, Gordon Andrew under a transpar- The Four Times Square Building in New York City uses ent cover. Evacu- Solar Electricity thin-film PV panels to reduce the building’s power load ated-tube collectors from the utility grid. Solar electricity or photovoltaic (PV) tech- are made up of nology converts sunlight directly into elec- rows of parallel, transparent glass tubes. tricity. Solar electricity has been a prime Each tube consists of a glass outer tube source of power for space vehicles since and an inner tube, or absorber, covered the inception of the space program. It has with a coating that absorbs solar energy also been used to power small electronics but inhibits heat loss. Concentrating collec- and rural and agricultural applications for tors for residential applications are usually three decades. During the last decade, a parabolic-shaped mirrors (like a trough) strong solar electric market has emerged that concentrate the sun’s energy on an for powering urban grid-connected homes absorber tube called a receiver that runs and buildings as a result of advances in along the axis of the mirrored trough and solar technology along with global contains a heat-transfer fluid. changes in electric industry restructuring.

All three types of collectors heat water by Although many types of solar electric sys- circulating household water or a heat-trans- tems are available today, they all consist of fer fluid such as a nontoxic antifreeze from basically three main items: modules that Passive solar building the collector to the water storage tanks. Col- convert sunlight into electricity; inverters lectors do this either passively or actively. that convert that electricity into alternat- techniques turn ing current so it can be used by most Passive solar water-heating systems use household appliances; and possibly or homes into huge natural or household water sometimes batteries that store excess elec- pressure to circulate water through a solar tricity produced by the system. The solar collectors. collector to a storage tank. They have no remainder of the system comprises equip- electric components that could break, a ment such as wiring, circuit breakers, and feature that generally makes them more support structures. reliable, easier to maintain, and possibly longer lasting than active systems. Today’s modules can be built into glass skylights and walls. Some modules resem- An active system uses an electric pump to ble traditional roof shingles, but they gen- circulate water or nontoxic antifreeze erate electricity, and some come with through the system. Active systems are built-in inverters. The solar modules avail- usually more expensive than passive sys- able today are more efficient and versatile tems, but they are also more efficient. than ever before. Active systems also can be easier to retrofit than passive systems because their storage In over 30 states, any additional power tanks do not need to be installed above or produced by a PV system, which is not close to the collectors. Also, the moving being used by a home or building, can be water in the system will not freeze in cold fed back to the electric grid through a . But because these systems use process known as . Net meter- electricity, they will not function in a ing allows electricity customers to pay . That’s why many active only for their “net” electricity, or the

5 amount of power consumed from their mirrors to concentrate sunlight onto the utility minus the power generated by their top of a tower, where a receiver sits. PV system. This metering arrangement Molten salt flowing through the receiver is allows consumers to realize full retail heated by the concentrated sunlight. The value for 100 percent of the PV energy salt’s heat is turned into electricity by a produced by their systems. conventional steam generator. Parabolic- trough systems concentrate the sun’s Grid-connected PV systems do not require energy through long, parabolic-shaped batteries. However, some grid connected mirrors. Sunlight is focused on a pipe systems use them for emergency backup filled with oil that runs down the axis of power. And of course in remote areas, solar the trough. When the oil gets hot, it is electricity is often a economic alternative to used to boil water in a conventional steam expensive distribution line extensions generator to produce electricity. A incurred by a customer first connecting to dish/engine system uses a mirrored dish the utility grid. Electricity produced by (similar in size to a large satellite dish). solar electric systems in remote locations is The dish-shaped surface focuses and con- stored in batteries. Batteries will usually centrates the sun’s heat onto a receiver at store electricity produced by a solar- the focal point of the dish (above and cen- electric system for up to three days. ter of the collectors). The receiver absorbs the sun’s heat and transfers it to a fluid What type of system to purchase will within an engine, where the heat causes depend on the energy-efficiency of your the fluid to expand against a piston to pro- home, your home’s location, and your duce mechanical power. The mechanical budget. Before you size your system, try power is then used to run a generator or reducing energy demand through energy- alternator to produce electricity. efficient measures. Purchasing energy-sav- ing appliances and , for example, will Concentrating solar technologies can be reduce your electrical demand and allow used to generate electricity for a variety of Bill Timmerman, NREL/PIX08982 you to purchase a smaller solar-electric applications, ranging from remote power This dish/Stirling solar system to meet your energy needs or get systems as small as a few kilowatts (kW) up power system in is capable of producing 25 kW more value from a larger system. Energy to grid-connected applications of 200 MW of electricity. efficiency allows you to start small and or more. A 354-MW power plant in South- then add on as your energy needs increase. ern California, which consists of nine trough power plants, meets the energy needs of Solar Thermal Electricity more than 350,000 people and is the Unlike solar-electric systems that convert world’s largest solar energy power plant. sunlight into electricity, solar thermal elec- tric systems convert the sun’s heat into Wind Energy electricity. This technology is used primar- For hundreds of years, people have used ily in large-scale power plants for power- to harness the wind’s energy. ing cities and communities, especially in Today’s wind turbines, which operate dif- Wind energy has been the Southwest where consistent hours of ferently from windmills, are a much more sunlight are greater than other parts of the efficient technology. the fastest growing United States. technology may look simple: source of energy since Concentrating (CSP) tech- the wind spins turbine blades around a nologies convert solar energy into electric- central hub; the hub is connected to a shaft, 1990… ity by using mirrors to focus sunlight onto which powers a generator to make electric- a component called a receiver. The ity. However, turbines are highly sophisti- receiver transfers the heat to a conven- cated power systems that capture the wind’s tional engine-generator—such as a steam energy by means of new blade designs or turbine—that generates electricity. airfoils. Modern, mechanical drive systems, combined with advanced generators, con- There are three types of CSP systems: vert that energy into electricity. power towers (central receivers), parabolic troughs, and dish/engine systems. A Wind turbines that provide electricity to power tower system uses a large field of the utility grid range in size from 50 kW to

6 1 or 2 MW. Large, simplicity, it doesn’t occur naturally as a utility-scale pro- gas on the Earth. jects can have hun- dreds of turbines Today, industry produces more than 4 tril- spread over many lion cubic feet of annually. Most acres of land. of this hydrogen is produced through a Small turbines, process called reforming, which involves below 50 kW, are the application of heat to separate hydro- used to charge bat- gen from carbon. Researchers are develop- teries, electrify ing highly efficient, advanced reformers to homes, pump produce hydrogen from natural gas for water for farms what’s called Proton Exchange Membrane and ranches, and fuel cells. power remote telecommunica- You can think of fuel cells as batteries that

Green Mountain Power Corporation, NREL/PIX05768 Green tions equipment. never lose their charge. Today, hydrogen The 6-MW Green Mountain power plant in Searsburg, Wind turbines can fuel cells offer tremendous potential to Vermont, consists of eleven 550-kW wind turbines. also be placed in produce electrical power for distributed the shallow water energy systems and vehicles. In the future, near a coastline if open land is limited, hydrogen could join electricity as an such as in Europe, and/or to take advan- important “”: storing, mov- tage of strong, offshore . ing, and delivering energy in a usable form to consumers. Renewable energy sources, Wind energy has been the fastest growing like the sun, can’t produce energy all the source of energy in the world since 1990, time. But hydrogen can store the renew- increasing at an average rate of over 25 able energy produced until it’s needed. percent per year. It’s a trend driven largely Hydrogen is high in by dramatic improvements in wind tech- Eventually, researchers would like to nology. Currently, wind energy capacity directly produce hydrogen from water energy, yet its use as amounts to about 2500 MW in the United using solar, wind, and biomass and bio- States. Good wind areas, which cover 6 logical technologies. a fuel produces water percent of the contiguous U.S. land area, could supply more than one and a half Energy times the 1993 electricity consumption of as the only emission. The ocean can produce two types of energy: the entire country. from the sun’s heat, and from the and waves. California now has the largest number of installed turbines. Many turbines are also Ocean thermal energy can be used for being installed across the Great Plains, many applications, including electricity reaching from Montana east to Minnesota generation. Electricity conversion systems and south through Texas, to take advantage use either the warm surface water or boil of its vast wind resource. North Dakota the seawater to turn a turbine, which acti- alone has enough wind to supply 36 percent vates a generator. of the total 1990 electricity consumption of the lower 48 states. Hawaii, Iowa, Min- The electricity conversion of both tidal nesota, Oregon, Texas, Washington, Wiscon- and wave energy usually involves sin, and Wyoming are among states where mechanical devices. A dam is typically wind energy use is rapidly increasing. used to convert tidal energy into electric- Hydrogen ity by forcing the water through turbines, activating a generator. Meanwhile, wave Hydrogen is high in energy, yet its use as a energy uses mechanical power to directly fuel produces water as the only emission. activate a generator, or to transfer to a Hydrogen is the universe’s most abundant working fluid, water, or air, which then NASA, NREL/PIX03814 NASA uses liquid hydrogen element and also its simplest. A hydrogen drives a turbine/generator. to launch its space shuttles atom consists of only one proton and and hydrogen fuel cells to one electron. Despite its abundance and Most of the research and development in provide them with electricity ocean energy is happening in Europe.

7 Resources The following are sources of additional information on Clean Energy Basics renewable energy. The list is not exhaustive, nor does the NREL mention of any resource constitute a recommendation or Web site: www.nrel.gov/clean_energy/ endorsement. Provides basic information on renewable energy technologies, Ask an Energy Expert including specific links for homeowners, small business own- ers, students, and teachers. DOE’s Energy Efficiency and Renewable Energy Clearinghouse (EREC) European Renewable Energy Exchange (EuroREX) P.O. Box 3048 Web site: www.eurorex.com Merrifield, VA 22116 Features information and news on renewable energy technol- Phone: 1-800-DOE-EREC (363-3732) ogy developments in Europe and around the world. TDD: 1-800-273-2957 Fax: (703) 893-0400 Planet Energy—The Renewable Energy Trail E-mail: [email protected] Department of Trade and Industry Online submittal form: www.eren.doe.gov/menus/ Web site: www.dti.gov.uk/renewable/ed_pack/ energyex.html index.html Consumer Energy Information Web site: www.eren.doe. Specifically gears its information for students and teachers, gov/consumerinfo/ from grade school through high school. Energy experts at EREC provide free general and technical Solstice information to the public on many topics and technologies per- taining to energy efficiency and renewable energy. Center for Renewable Energy and Sustainable Technology (CREST) DOE’s Energy Efficiency and Renewable Energy Web site: http://solstice.crest.org Network (EREN) Provides an online source of information on renewable energy Web site: www.eren.doe.gov and technology development. Your comprehensive online resource for DOE’s energy effi- ciency and renewable energy information. Further Reading Achieving Energy Independence—One Step at a Time, J. Organizations Yago, Dunimis Technology, 1999, 190 pp. Center for Energy Efficiency and Renewable Energy (CEERT) Charging Ahead: The Business of Renewable Energy and 1100 Eleventh St., Suite 311 What It Means for America, J. Berger and L. Thurow, Uni- Sacramento, CA 95814 versity of California Press, 1998, 416 pp. Phone (916) 442-7785; Fax (916) 447-2940 Clean Energy Choices: Tips on Buying and Using Renewable E-mail: [email protected] Energy at Home, DOE Office of Energy Efficiency and Web site: www.cleanpower.org Renewable Energy, 2000, 48 pp. Print copy available Promotes the development of renewable energy technologies from EREC (see “Ask an Energy Expert” above), and a and resources. PDF is available at www.nrel.gov/docs/fy00osti/ 27684.pdf. National Renewable Energy Laboratory (NREL) 1617 Cole Blvd. The Solar Living Sourcebook: The Complete Guide Golden, CO 80401 to Renewable Energy Technologies and , D. Web site: www.nrel.gov Pratt ed., Real Goods, 1999, 562 pp. DOE-lab devoted to researching and developing renewable energy and energy efficiency technologies. Renewable Project (REPP) 1612 K St. NW, Suite 202 Washington, DC 20006 Phone: (202) 293-2898; Fax: (202) 293-5857 Web site: www.repp.org Works to advance renewable energy technologies. Web Sites CADDET Renewable Energy Web site: www.caddet-re.org Provides technical information on renewable energy projects and technologies from around the world.

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