chapter 6
RENEWABLE ENERGY

RENEWABLE ENERGY DEFINED

Imagine energy sources that use no oil, produce no pollution, cannot be affected by political events and cartels, create no radioactive waste, and yet are economical. Although it sounds impossible, some experts claim that technological advances could make wide use of renewable energy sources possible within a few decades. Renewable energy is energy that is naturally regenerated and is, therefore, virtually unlimited. Sources include the sun (solar), wind, water (hydropower), vegetation (biomass), and the heat of the earth (geothermal).

Solar energy, wind energy, hydropower, and geothermal power are all renewable, inexpensive, and clean sources of energy. Each of these alternative energy sources has advantages and disadvantages, and many observers hope that one or more of them may eventually provide a substantially better energy source than conventional fossil fuels. As the United States and the rest of the world continue to expand their energy needs—putting a strain on the environment and nonrenewable resources—alternative sources of energy continue to be explored.

A HISTORICAL PERSPECTIVE

Before the eighteenth century, most energy came from renewable sources. People burned wood for heat, used sails to harness the wind and propel boats, and installed water wheels on streams to grind grain. The large-scale shift to nonrenewable energy sources began in the 1700s with the Industrial Revolution, a period marked by the rise of factories, first in Europe and then in North America. As demand for energy grew, coal replaced wood as the main fuel. Coal was the most efficient fuel for the steam engine, one of the most important inventions of the Industrial Revolution.

Until the early 1970s most Americans were unconcerned about the sources of the nation's energy. Supplies of coal and oil, which together provided more than 90% of U.S. energy, were believed to be plentiful. The decades preceding the 1970s were characterized by cheap gasoline and little public discussion of energy conservation.

That carefree approach to energy consumption ended in the 1970s. A fuel oil crisis made Americans more aware of the importance of developing alternative sources of energy to supplement and perhaps eventually even replace fossil fuels. In major cities throughout the United States, gasoline rationing became commonplace, lower heat settings for offices and living quarters were encouraged, and people waited in line to fill their gas tanks. In a country where mobility and personal transportation were highly valued, the oil crisis was a shocking reality for many Americans. As a result, the administration of President Jimmy Carter encouraged federal funding for research into alternative energy sources.

In 1978 the U.S. Congress passed the Public Utilities Regulatory Policies Act (PURPA; PL 95-617), which was designed to help the struggling alternative energy industry. The act exempted small alternative producers from state and federal utility regulations and required existing local utilities to buy electricity from them. The renewable energy industries responded by growing rapidly, gaining experience, improving technologies, and lowering costs. This act was the single most important factor in the development of the commercial renewable energy market.

In the 1980s President Ronald Reagan decided that private-sector financing for the short-term development of alternative energy sources was better than public-sector financing. As a result, he proposed the reduction or elimination of federal expenditures for alternative energy sources. Although funds were severely cut, the U.S. Department of Energy (DOE) continued to support some research and development to explore alternate sources of energy. President Bill Clinton's administration reemphasized the importance of renewable energy and increased funding in several areas. The George W. Bush administration believed that renewable and alternative fuels offer hope for the future but also considered that only a small portion of America's energy needs as of the early 2000s were offset by renewables. The Bush administration supported funding for research and development in renewable technologies and tax credits for the purchase of hybrid and fuel cell cars.

DOMESTIC RENEWABLE ENERGY USAGE

Renewable energy contributes only a small portion of the nation's energy supply. In 2003 the United States consumed approximately 6.2 quadrillion Btu of renewable energy, about 6% of the nation's total energy consumption. (See Table 6.1.) Biomass sources (wood, waste, and alcohol) contributed 2.9 quadrillion Btu, while hydroelectric power provided 2.8 quadrillion Btu. Together, biomass and hydroelectric power provided 92% of renewable energy in 2003, or around 6% of all energy as shown in Figure 6.1. Geothermal energy was the third largest source, with about 0.3 quadrillion Btu. Solar power contributed 0.06 quadrillion Btu, and wind provided 0.1 quadrillion Btu.

BIOMASS ENERGY

Biomass refers to organic material such as plant and animal waste, wood, seaweed and algae, and garbage. The use of biomass is not without environmental problems. Deforestation can occur from widespread wood use if forests are clear-cut, resulting in the possibility of soil erosion and mudslides. Burning wood, like burning fossil fuels, also pollutes the environment. Biomass can be burned directly or converted to biofuel by thermochemical conversion and biochemical conversion.

Direct Burning

Direct combustion is the easiest and most commonly used method of using biomass as fuel. Materials such as dry wood or agricultural wastes are chopped and burned to produce steam, electricity, or heat for industries, utilities, and homes. Industrial-size wood boilers are operating throughout the country, and the Department of Energy (DOE) maintains that many more will be built during the next decade. The burning of agricultural wastes is also becoming more widespread. In Florida, sugarcane producers use the residue from the cane to generate much of their energy.

Wood burning in stoves and fireplaces is another example of direct burning of biomass for energy, in this case heat. In the United States, residential use of wood as fuel generated 359 trillion Btu in 2003. In comparison, the generation of Btu from burning wood in the home in the 1980s was about 850–950 trillion Btu according to the Energy Information Administration's Annual Energy Review 2003.

FIGURE 6.1

Wood burning in stoves and fireplaces is another example of direct burning of biomass for energy, in this case heat. In the United States, residential use of wood as fuel generated 359 trillion Btu in 2003. In comparison, the generation of Btu from burning wood in the home in the 1980s ranged from about 850–950 trillion Btu annually according to the Energy Information Administration's Annual Energy Review 2003.

Thermochemical Conversion

Thermochemical conversion involves heating bio-mass in an oxygen-free or low-oxygen atmosphere, transforming the material into simpler substances that can be used as fuels. Products such as charcoal and methanol are produced this way.

Biochemical Conversion

Biochemical conversion uses enzymes, fungi, or other microorganisms to convert high-moisture biomass into either liquid or gaseous fuels. Bacteria convert manure, agricultural wastes, paper, and algae into methane, which is used as fuel. Sewage treatment plants have used anaerobic

TABLE 6.1

(oxygen-free) digestion for many years to generate methane gas. Small-scale digesters have been used on farms, primarily in Europe and Asia, for hundreds of years. Biogas pits (a biomass-based technology) are a significant source of energy in China.

Another type of biochemical conversion process, fermentation, uses yeast to decompose carbohydrates, yielding ethyl alcohol (ethanol) and carbon dioxide. Sugar crops, grains (corn, in particular), potatoes, and other starchy crops commonly supply the sugar for ethanol production.

Ethanol and Methanol

Ethanol (ethyl alcohol) is a colorless, nearly odorless, flammable liquid derived from fermenting plant material that contains carbohydrates in the form of sugar. Most of the ethanol manufactured for use as fuel in the United States is derived from corn, wood, and sugar. Gasohol is a product formed by mixing ethanol and gasoline. There are three types of gasohol: 10% gasohol, which is a mixture of 10% ethanol and 90% gasoline; 7.7% gasohol, which is at least 7.7% ethanol but less than 10%; and 5.7% gasohol, which is at least 5.7% ethanol but less than 7.7%. The Federal Highway Administration estimated that in 2002 nearly 21 billion gallons of gasohol were used by Americans, up from 17.4 billion gallons in 2001 and 16.3 billion gallons in 2000.

Automobiles can run on gasohol and can be built to run directly on ethanol or on any mixture of ethanol and gasoline. However, ethanol is difficult and expensive to produce in bulk. The development of ethanol as a fuel source may depend more upon the political support of legislators from farming states and a desire for some independence from foreign oil rather than upon savings at the gas pump.

Some scientists believe ethanol made from wood, sawdust, corncobs, or rice hulls could liberate the alcohol fuel industry from its dependence on food crops, such as corn and sugarcane. Worldwide, enough corncobs and rice hulls are left over from annual crop production to produce more than forty billion gallons of ethanol.

Advocates of wood-derived ethanol believe that it could eventually be a sustainable liquid fuel industry that does not rely on pollution-generating fossil fuels. For instance, if new trees were planted to replace those that were cut for fuel, they would be available for later harvesting while at the same time alleviating global warming with their carbon dioxide-processing function. However, other scientists warn that an increased demand for wood for transportation fuels might accelerate the destruction of old-growth forests and endanger ecosystems.

Methanol (methyl alcohol) fuels have also been tested successfully. Using methanol instead of diesel fuel virtually eliminates sulfur emissions and reduces other environmental pollutants usually emitted from trucks and buses. Producing methanol from biofuels, however, is costly.

Burning biofuels in vehicle engines is part of the "carbon cycle" in which the earth's vegetation can, in turn, make use of the products of automobile combustion. (See Figure 6.2.) Automobile combustion generated from fossil fuels, however, contains pollutants. In addition, generating excessive amounts of carbon dioxide from either fossil fuels or biofuels is thought to add to global warming because this gas acts as a "blanket," trapping heat between the earth and the atmosphere.

Municipal Waste Recovery

Each year millions of tons of garbage are buried in landfills and city dumps. This method of disposal is becoming increasingly costly as many landfills across the nation near capacity. Many communities discovered that they could solve both problems—cost and capacity—by constructing waste-to-energy plants. Not only is the garbage burned and reduced in volume by 90%, but also energy in the form of steam or electricity is generated in a cost-effective way, and the potential energy benefit is significant. Use of municipal waste as fuel has increased steadily since the 1980s. According to EIA figures, municipal waste (including landfill gas, sludge waste, tires, and agricultural by-products) generated 88 trillion Btu of energy in 1981, which grew to 558 trillion Btu by 2003.

The two most common waste-to-energy plant designs are the mass burn (also called direct combustion) system and the refuse derived fuel (RDF) system.

mass burn systems. Most waste-to-energy plants in the United States use the mass burn system. This system's advantage is that the waste does not have to be sorted or prepared before burning, except for removing obviously noncombustible, oversized objects. The mass burn eliminates expensive sorting, shredding, and transportation machinery that may be prone to break down.

In mass burn systems, waste is carried to the plant in trash trucks and dropped into a storage pit. Large overhead cranes lift the garbage into a furnace feed hopper that controls the amount and rate of waste that is fed into the furnace. Next, the garbage is moved through a combustion zone so that it burns to the greatest extent possible. The burning waste produces heat, and that heat is used to produce steam. The steam can be used directly for industrial needs or can be sent through a turbine to power a generator to produce electricity.

refuse derived fuel (rdf) systems. RDF systems process waste to remove noncombustible objects and to create homogeneous and uniformly sized fuel. Large items such as bedsprings, dangerous materials, and flammable liquids are removed by hand. The trash is then shredded and carried to a screen to remove glass, rocks,

FIGURE 6.2

and other material that cannot be burned. The remaining material is usually sifted a second time with an air separator to yield fluff. The fluff is sent to storage bins before being burned, or it can be compressed into pellets or briquettes for long-term storage. This fuel can be used as an energy source by itself in a variety of systems, or it can be used with other fuels, such as coal or wood.

performance of waste-to-energy systems. Most waste-to-energy systems can produce two to four pounds of steam for every pound of garbage burned. A 1,000-ton-per-day mass burn system will burn an average of 310,250 tons of trash each year and will recover two trillion Btu of energy. In addition, the plant will emit 96,000 tons of ash (32% of waste input) for landfill disposal. An RDF plant produces less ash but sends almost the same amount of waste to the landfill because of the noncombustibles that accumulate in the separation process before burning.

disadvantages of waste-to-energy plants. The major problem with increasing the use of municipal waste-to-energy plants is their effect on the environment. The emission of particles into the air is partially controlled by electrostatic precipitators, and many gases can be eliminated by proper combustion techniques. There is concern, however, about the amounts of dioxin (a very dangerous air pollutant) and other toxins that are often emitted from these plants. Noise from trucks, fans, and processing equipment at these plants can also be unpleasant for nearby residents.

Landfill Gas Recovery

Landfills contain a large amount of biodegradable matter that is compacted and covered with soil. Bacteria called methanogens thrive in this oxygen-depleted environment. They metabolize the biodegradable matter in the landfill, producing methane gas and carbon dioxide as byproducts. In the past, as landfills aged, these gases built up and leaked out. This gas leakage prompted some communities to drill holes in landfills and burn off the methane to prevent dangerously large amounts from exploding.

The energy crisis of the 1970s made landfill methane gas an energy resource too valuable to waste, and efforts were made to find an inexpensive way to tap the gas. The first landfill gas recovery site was finished in 1975 at the Palos Verdes Landfill in Rolling Hills Estates, California.

In a typical operation, garbage is allowed to decompose for several months. When a sufficient amount of methane gas has developed, it is piped out to a generating plant, where it is turned into electricity. In its purest form, methane gas is equivalent to natural gas and can be used in exactly the same way. Depending on the extraction rates, most sites can produce gas for about 20 years. The advantages of tapping gas from a landfill go beyond the energy provided by the methane, as extraction reduces landfill odors and the chances of explosions.

HYDROPOWER

Hydropower, the energy that comes from the natural flow of water, is the world's largest renewable energy source. The energy of falling water or flowing water is converted into mechanical energy and then to electrical energy. In the past, flowing water turned waterwheels to grind grain or turn saws, but today flowing water is used to turn modern turbines. Hydropower is a renewable, nonpolluting, and reliable energy source.

Advantages and Disadvantages of Using Hydropower Energy

At present, hydropower is the only means of storing large quantities of electrical energy for almost instant use. This is done by holding water in a large reservoir behind a dam, with a hydroelectric power plant below. The dam creates a height from which water flows. The fast-moving water pushes the turbine blades that turn the rotor part of the electric generator. Whenever power is needed at peak times, the valves are opened, and turbine generators quickly produce power.

Nearly all the best sites for large hydropower plants are already being put to use in the United States. Small hydropower plants are expensive to build but eventually become cost-efficient because of their low operating costs. One of the disadvantages of small hydropower generators is their reliance on rain and melting snow to fill reservoirs because some years bring drought conditions. Additionally, U.S. environmental groups strongly protest the construction of new dams in America. Ecologists express concern that dams ruin streams, dry up waterfalls, and interfere with aquatic life habitats.

New Directions in Hydropower Energy

The United States and Europe have developed a major proportion of their hydroelectric potential. Large-scale hydropower development has slowed considerably in the United States. The last federally funded hydropower dam constructed in the United States was the Corps of Engineers' Richard B. Russell Dam and Lake, which is located on the Savannah River and borders South Carolina and Georgia. The project was authorized in 1966 and completed in 1986. However, expansion and efficiency improvements at existing dams still offer significant potential for additional hydropower capacity and energy. Until recently in the United States, dams were usually funded entirely with federal monies. Since 1986, however, local governments must contribute half of the cost of any new dam proposed in the United States. Hydropower's contribution to U.S. energy generation should remain relatively constant, although existing sites can become more efficient as new generators are added. Any new major supplies of hydroelectric power for the United States will likely come from Canada.

Most of the new development in hydropower is occurring in the Third World, as developing nations see it as an effective method of supplying power to growing populations. Most of these hydropower-development programs are massive public-works projects requiring huge amounts of money, which is mostly borrowed from the developed world. Third World leaders believe that hydroelectric dams are worth the cost and potential environmental threats because they bring cheap electric power to their citizenry.

GEOTHERMAL ENERGY

Since ancient times, humans have exploited the earth's natural hot water sources. Although bubbling hot springs became public baths as early as ancient Rome, using hot water and underground steam to produce power is a relatively recent development. Electricity was first generated from natural steam in Italy in 1904. The world's first steam power plant was built in 1958 in a volcanic region of New Zealand. A field of twenty-eight geothermal power plants covering thirty square miles in northern California was completed in 1960.

What Is Geothermal Energy?

Geothermal energy is the natural, internal heat of the earth trapped in rock formations deep underground. Only a fraction of this vast storehouse of energy can be extracted, usually through large fractures in the earth's crust. Hot springs, geysers, and fumaroles (holes in or near volcanoes from which vapor escapes) are the most easily exploitable sources of geothermal energy. (See Figure 6.3.) Geothermal reservoirs provide hot water or steam that can be used for heating buildings, processing food, and generating electricity.

To produce power from a geothermal energy source, pressurized steam or hot water is extracted from the earth and directed toward turbines. The electricity produced by the turbines is then fed into a utility grid and distributed to residential and commercial customers.

Types of Geothermal Energy

Like most natural energy sources, geothermal energy is usable only when it is concentrated in one spot, in this

FIGURE 6.3

case in what is called a "thermal reservoir." The four basic categories of thermal reservoirs are hydrothermal reservoirs, dry rock, geopressurized reservoirs, and magma resources. Most of the known reservoirs for geothermal power in the United States are located west of the Mississippi River, and the highest-temperature geothermal resources occur mostly west of the Rocky Mountains. According to the Energy Information Administration, in 2002 geothermal resources produced nearly 13.4 billion kilowatt hours, which is a little less than 4% of the energy generated by renewable sources.

hydrothermal reservoirs. Hydrothermal reservoirs consist of a heat source covered by a permeable formation through which water circulates. Steam is produced when hot water boils underground and some of the steam escapes to the surface under pressure. Once at the surface, impurities and tiny rock particles are removed, and the steam is piped directly to the electrical generating station. These systems are the cheapest and simplest form of geothermal energy. The Geysers, ninety miles north of San Francisco, California, are the most famous example of this type. The Geysers Geothermal Field is the world's largest source of geothermal power, according to the Energy Information Administration.

dry rock. Dry rock formations are the most common geothermal source, especially in the West. To tap this source of energy, water is injected into hot rock formations that have been fractured and the resulting steam or water is collected.

geopressurized reservoirs. Geopressurized reservoirs are sedimentary formations containing hot water and methane gas. Supplies of geopressurized energy remain uncertain, and drilling is expensive. Scientists hope that advancing technology will eventually permit the commercial exploitation of the methane content in these reservoirs.

magma resources. Magma resources are found from ten thousand to thirty-three thousand feet below the earth's surface, where molten or partially liquefied rock is located. Because magma is so hot, ranging from 1,650 to 2,200 degrees Fahrenheit, it is a good geothermal resource. The process for extracting energy from magma is still in the experimental stages.

Domestic Production of Geothermal Energy

Geothermal energy ranked third in renewable energy production in the United States in 2003, after biomass (wood, waste, alcohol) and hydroelectric power. (See Table 6.1.) According to the International Geothermal Association, in 2002 the United States had 28% of the installed geothermal generating capacity of the world, but most of the easily exploited geothermal reserves in the United States have already been developed. In addition, utility companies and independent power producers are arguing over who should build additional generating capacity and what prices should be paid for the power. Continued growth in the American market depends on the regulatory environment, oil price trends, and the success of unproven technologies for economically exploiting some of the presently inaccessible geothermal reserves.

International Production of Geothermal Energy

Since 1970, worldwide geothermal electrical generating capacity has more than tripled. According to the EIA's Annual Energy Review 2003, geothermal energy made up about 1.2% of world electrical production in 2002. Geothermal sources worldwide produce little more than the energy output of ten average-size coal-fired power plants.

World geothermal reserves are immense but unevenly distributed. They fall mostly in seismically active areas at the margins or borders of the earth's nine tectonic plates. Currently, exploited reserves represent only a small fraction of the overall potential—many countries are believed to have in excess of 100,000 megawatts of geothermal energy available.

The World Geothermal Congress (WGC), with representation by delegates from sixty countries, met in Kyushu and Tohoku, Japan in 2000. At that meeting the WGC noted that nearly 90% of homes and other buildings in Iceland are heated by geothermal waters, and approximately 26% of electrical power generation in the Philippines comes from geothermal steam. The WGC supports the use of geothermal energy; one of its goals is to replicate such high use of geothermal resources in other countries. The next meeting of WGC is in 2005.

Disadvantages of Geothermal Energy

Geothermal plants must be built near a geothermal source, are not very efficient, produce unpleasant odors from sulfur released in processing, generate noise, are inaccessible for most states, release potentially harmful pollutants (hydrogen sulfide, ammonia, and radon), and release poisonous arsenic or boron often found in geothermal waters. Serious environmental concerns have been raised over the release of chemical compounds, the potential contamination of water sources, the collapse of the land surface around the area from which the water is being drained, and potential water shortages resulting from massive withdrawals of water.

WIND ENERGY

Winds are created by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and the rotation of the earth. Winds are strongly influenced by local terrain, water bodies, weather patterns, vegetation, and other factors. Wind flow, when "harvested" by wind turbines, can be used to generate electricity.

Early windmills produced mechanical energy to pump water and run grain and sawmills. In the late 1890s, Americans began experimenting with wind power to generate electricity. Their early efforts produced enough electricity to light one or two modern light bulbs.

Compared to the pinwheel-shaped farm windmills that can still be seen dotting the American rural landscape, today's state-of-the-art wind turbines look more like airplane propellers. Their sleek, high-tech fiberglass design and aerodynamics allow them to generate an abundance of electricity while they also produce mechanical energy and heat.

Beginning in the 1990s, industrial and developing countries alike have started using wind power as a source of electricity to complement existing power sources and to bring electricity to remote regions. Wind turbines cost less to install per unit of kilowatt capacity than either coal or nuclear facilities. After installing a windmill, there are few additional costs, as the fuel (wind) is free.

Wind speeds are generally highest and most consistent in mountain passes and along coastlines. Europe has the greatest coastal wind resources, and clusters of wind turbines, or wind farms, are being developed there and in Asia. Denmark, the Netherlands, China, and India are especially interested in fostering the development of domestic wind industries (International Energy Outlook 2004, Energy Information Administration). As of 2004, electricity-producing wind turbines operate in ninety-five countries. In the United States it is estimated that sufficient wind energy is available to provide more than one trillion kilowatt-hours of electricity annually, or about 27% of the total used in 2003.

Domestic Energy Production by Wind Turbines

According to the EIA, wind is the world's fastestgrowing renewable energy source (International Energy Outlook 2004). Although wind power has not been adopted

FIGURE 6.4

widely in the United States, U.S. companies export turbines to Spain, the Netherlands, Great Britain, India, and China.

In the United States, the wind industry began in California in 1981 with the erection of 144 relatively small turbines capable of generating a combined total of seven megawatts of electricity. Within a year the number of turbines had increased ten times, and by 1986 they had multiplied one-hundred-fold. In Annual Energy Outlook 2004, the EIA projects wind power capacity in the United States to grow more than three-fold from 2003 to 2025.

Wind technology exploded in California in the 1980s, where about 95% of the installed wind capacity in the United States used to be located. During 1998 and 1999, however, wind farm activity expanded into other states; less than 32% of new wind power construction was located in California. This increasing activity outside California was motivated by financial incentives (such as the wind-energy-production tax credit), regulatory incentives, and state mandates (in Iowa and Minnesota). In 1999 Iowa, Minnesota, and Texas each had capacity additions exceeding one hundred megawatts. According to the American Wind Energy Association, by 2004 these three states had been joined by nine others in exceeding one hundred megawatts of installed capacity. These twelve states—Washington, Oregon, California, Wyoming, Colorado, New Mexico, Texas, Iowa, Minnesota, Oklahoma, Kansas, and Pennsylvania—contain 94% of the U.S. wind energy potential. The wind power generation capacity of the United States in 2003 is shown in Figure 6.4. The total installed generating capacity of the U.S. is 6,374 megawatts, and wind power plants operate in thirty-two states.

Refinements in wind-turbine technology may enable a substantial portion of the nation's electricity to be produced by wind energy. Use of this technology is being encouraged by the initiative "Wind Powering America," which was announced in June 1999 by the U.S. Secretary of Energy. The stated goals of the program are to have eighty thousand megawatts of wind power generation capacity in place by 2020 and to have wind power provide 5% of the nation's electricity generation.

An added incentive to developing wind technology is continuing tax credits. The wind-energy-production tax credit provided by the Energy Policy Act (EPACT) of 1992 was scheduled to expire in 1999 but was extended to the end of 2003. A provision in the 2003 EPACT bill includes a bipartisan plan for extending the tax credit through 2006.

International Development of Wind Energy

During the decade following the 1973 oil embargo, more than ten thousand wind machines were installed worldwide, ranging in size from portable units to multi-megawatt turbines. In the villages of developing nations, small wind turbines recharge batteries and provide essential services. In China small wind turbines allow people to watch their favorite television shows, an activity that has increased wind energy demand. In fact, in 2001 China was the world's largest manufacturer of small wind turbines.

Global wind-power-generating capacity was about 39,000 megawatts in 2003, up from 23,300 megawatts in 2001, 7,200 megawatts in 1997, and 3,000 megawatts in 1993. Germany, Spain, and Denmark are the fastest growing wind producers in the world, and the United Kingdom, Ireland, and Portugal all are experiencing a surge in installed wind capacity ("The Current Status of the Wind Industry," European Wind Energy Association, http://www.ewea.org/ [accessed January 14, 2005]).

Interest in wind energy has been driven, in part, by the declining cost of capturing wind energy. From more than thirty-eight cents per kilowatt-hour in 1980, wind energy prices declined to about four cents per kilowatt-hour in 2002 for new turbines at sites with strong winds (Lester R. Brown, "Wind Power Set to Become World's Leading Energy Source," Earth Policy Institute, June 25, 2003). Decreasing costs could make wind power competitive with gas and coal power plants, even before considering wind's environmental advantages.

Advantages and Disadvantages of Wind Energy

The main problem with wind energy is that the wind does not always blow. Some people object to the whirring noise of wind turbines or do not like to see wind turbines clustered in mountain passes and along shorelines because they interfere with scenic views. Environmentalists have charged that wind turbines are responsible for the loss of thousands of endangered birds that fly into the blades, as birds frequently use windy passages in their travel patterns.

However, generating electricity with wind offers many environmental advantages. Wind farms do not emit climate-altering carbon dioxide, acid-rain-forming pollutants, respiratory irritants, or nuclear waste. Because wind farms do not require water to operate, they are especially well-suited to semi-arid and arid regions.

SOLAR ENERGY

Ancient Greek and Chinese civilizations used glass and mirrors to direct the sun's rays to start fires. Solar energy (energy from the sun) is a renewable, widely available energy source that does not generate greenhouse gases or radioactive waste. Solar-powered cars have competed in long-distance races, and solar energy has been used routinely for many years to power spacecraft. Although many people consider solar energy a product of the space age, architectural researchers at the Massachusetts Institute of Technology built the first solar house in 1939.

Solar radiation is nearly constant outside the earth's atmosphere, but the amount of solar energy reaching any point on earth varies with changing atmospheric conditions, such as clouds and dust, and the changing position of the earth relative to the sun. In the United States, exposure to the sun's rays is greatest in the West and Southwest regions. Nevertheless, almost all U.S. regions have solar resources that can be used. (See Figure 6.5.)

Passive and Active Solar Energy Collection Systems

Passive solar energy systems, such as greenhouses or windows with a southern exposure, use heat flow, evaporation, or other natural processes to collect and transfer heat. (See Figure 6.6.) They are considered the least costly and least difficult solar systems to implement.

Active solar systems use mechanical methods to control the energy process. (See Figure 6.6.) They require collectors and storage devices as well as motors, pumps, and valves to operate the systems that transfer heat. Collectors consist of an absorbing plate that transfers the sun's heat to a working fluid (liquid or gas), a translucent cover plate that prevents the heat from radiating back into the atmosphere, and insulation on the back of the collector panel to further reduce heat loss. Excess solar energy is transferred to a storage facility so it may be used to provide power on cloudy days. In both active and passive systems, the conversion of solar energy into a form of power is made at the site where it is used. The most common and least expensive active solar systems are used for heating water.

Solar Thermal Energy Systems

A solar thermal energy system uses intensified sunlight to heat water or other fluids to temperatures of more than 750 degrees Fahrenheit. Mirrors or lenses constantly track the sun's position and focus its rays onto solar receivers that contain fluid. Solar heat is transferred to the water, which in turn powers an electric generator. In a distributed solar thermal system, the collected energy powers

FIGURE 6.5

irrigation pumps, providing electricity for small communities or capturing normally wasted heat from the sun in industrial areas. In a central solar thermal system, the energy is collected at a central location and used by utility networks for a large number of customers.

Other solar thermal energy systems include solar ponds and trough systems. Solar ponds are lined ponds filled with water and salt. Because salt water is denser than fresh water, the salt water on the bottom absorbs the heat, and the fresh water on top keeps the salt water contained and traps the heat. Trough systems use U-shaped mirrors to concentrate the sunshine on water or oil-filled tubes.

Photovoltaic Conversion Systems

The photovoltaic (PV) cell solar energy system converts sunlight directly into electricity without the use of mechanical generators. PV cells have no moving parts, are easy to install, require little maintenance, do not pollute the air, and can last up to twenty years. PV cells are commonly used to power small devices, such as watches or calculators. They are also being used on a larger scale to provide electricity for rural households, recreational vehicles, and businesses. Solar panels using photovoltaic cells have generated electricity for space stations and satellites for many years.

Since PV systems produce electricity only when the sun is shining, a backup energy supply is required. PV cells produce the most power around noon, when sunlight is the most intense. A photovoltaic system typically includes storage batteries that provide electricity during cloudy days and at night.

The use of photovoltaic technology is expanding both in the United States and abroad. PV systems have low operating costs because there are no turbines or other moving parts, and maintenance is minimal. PV cell systems are nonpolluting and silent and can be operated by computer. Above all, the fuel source (sunshine) is free and plentiful. The main disadvantage of photovoltaic cell energy systems is the initial cost. Although the price has fallen considerably, PV cells are still too expensive for widespread use. PV systems also use some toxic materials, which may cause environmental problems.

FIGURE 6.6

Solar Energy Usage

Because it is difficult to measure directly the use of solar energy, shipments of solar equipment can be used as an indicator of use. From a high of eighty-four low-temperature solar collector manufacturers in 1979, this number dropped to only thirteen manufacturers in 1999. Total shipments of solar thermal collectors peaked in 1981 at more than 21 million square feet, fell to a low of 6.6 million square feet in 1991, and rose again to 11.7 million square feet in 2002. (See Figure 6.7.)

Based on 2002 figures most of the solar thermal collectors sold are for residential purposes (see Figure 6.8) and most are sold in sunbelt states. The majority of solar thermal collectors shipped in 2002 were used for heating swimming pools, and a smaller percentage for hot water. (See Figure 6.9.) The market for solar energy space heating has virtually disappeared. Only a small proportion of solar thermal collectors are used for commercial purposes, though some state and municipal power companies have added solar energy systems as adjuncts to their regular power sources during peak hours.

Solar Power as an International Rural Solution

Rural areas are more expensive to serve with energy than cities, and electrification has been slow to reach many people in rural areas of developing countries. In the United States, it was only in 1935, after the Rural Electrification Administration provided low-cost financing to rural electric cooperatives, that most farmers received power. In places such as western China, the Himalayan foothills, and the Amazon basin, the cost of connecting new rural customers

FIGURE 6.7

to electricity grids remains very high. Furthermore, state-owned power systems have been poorly managed in many countries. This has left many national power systems all but bankrupt, and blackouts have become common.

In India blackouts are so common that many factories and other businesses have, at great expense, set up their own private systems, using natural gas, propane, or fuel oil. Although rural families do not have access to those systems, they do have sunlight. In most tropical countries, considerable sunlight falls on rooftops. Electricity produced by solar photovoltaic cells was initially too expensive—as much as a thousand times more than that from conventional plants—but it has continually fallen in price.

Future Development Trends

Interest in photovoltaic solar energy systems is particularly high in rural and remote areas where it is impractical to extend traditional electrical power lines. In some remote areas, PV cells are used as independent power sources for communications or for the operation of water pumps or refrigerators.

Although solar power still costs more than three times as much as fossil fuel energy, utilities could turn to solar energy to provide "peaking power" on extremely hot or cold days. In the long run, some people believe that building

FIGURE 6.8

solar energy systems to provide peak power capacity would be cheaper than building the new and expensive diesel fuel generators that are now used.

Advantages and Disadvantages of Solar Energy

The primary advantage of solar energy is its inexhaustible supply, while its primary disadvantage is its reliance on a consistently sunny climate to provide continuous electrical power, which is only possible in limited areas. In addition, a large amount of land area is necessary for the most efficient collection of solar energy by electricity plants. Experts estimate that a new thermal energy plant would have a higher cost of production than a conventional coal-fired plant.

POWER FROM THE OCEAN

The potential power of the world's oceans is unknown. Because the ocean is not as easily controlled as a river or water that is directed through canals into turbines, unlocking that potential power is far more challenging. Three ideas being considered are tidal plants, wave power, and ocean thermal energy conversion (OTEC).

Tidal Power

The tidal plant uses the power generated by the tidal flow of water as it ebbs, or flows back out to sea. A minimum tidal range of three to five yards is generally considered

FIGURE 6.9

necessary for an economically feasible plant. (The tidal range is the difference in height between consecutive high and low tides.) Canada has built a small 40-megawatt unit at the Bay of Fundy, with its fifteen-yard tidal range, the largest range in the world, and is considering building a larger unit there. The largest existing tidal facility is the 240-megawatt plant at the La Rance estuary in northern France, built in 1965. Russia has a small 400-kilowatt plant near Murmansk, close to the Barents Sea. The world's first offshore tidal energy turbine near Devon, England, began producing energy in 2003.

Wave Energy

Norway has two operating wave power stations at Toftestallen on its Atlantic coast. These systems were the first significant oscillating water column (OWC) systems and they work like this: The arrival of a wave forces water up a hollow sixty-five-foot tower, displacing the air already in the tower. This air rushes out of the top through a turbine. The rotors of that turbine then spin, generating electricity. When the wave falls back and the water level falls, air is sucked back in through the turbine, again generating electricity. OWCs have been built and tested in Japan, Norway, India, China, Scotland, and Portugal.

A second type of wave energy power plant uses the overflow of high waves. As the wave splashes against the top of a dam, some of the water goes over and is trapped in a reservoir on the other side. The water is then directed through a turbine as it flows back to the sea.

These two kinds of plants are experimental. Several projects are under way in Japan and the Pacific region to determine a way to use the potential of the huge waves of the Pacific. Although considerable progress has been made in the research and development of this technology, several challenging engineering problems remain to be solved.

Ocean Thermal Energy Conversion (OTEC)

Ocean thermal energy conversion, or OTEC, uses the temperature difference between the ocean's warm surface water and the cooler water in its depths to produce heat energy that can power a heat engine to produce electricity. OTEC systems can be installed on ships, barges, or offshore platforms with underwater cables that transmit electricity to shore.

HYDROGEN: A FUEL OF THE FUTURE?

Hydrogen, the lightest and most abundant chemical element, is the ideal fuel from the environmental point of view. Its combustion produces only water vapor, and it is entirely carbon-free. Three-quarters of the mass of the universe is hydrogen, so in theory the supply is ample. However, the combustible form of hydrogen is a gas and is not found in nature. The many compounds containing hydrogen—water, for example—cannot be converted into pure hydrogen without the expenditure of energy. The amount of energy that would be required to make gas is about the same as the amount of energy that would be obtained by the combustion of the hydrogen. Therefore, with today's technology, little or nothing could be gained from an energy point of view.

Scientists, however, are researching ways to produce hydrogen gas economically. Whether this will come from fusion, solar energy, or elsewhere is not possible to predict now. Scientists have considered the possibility of a transition to hydrogen for more than a century, and today many see hydrogen as the logical "third-wave" fuel, with hydrogen gas following oil, just as oil replaced coal decades earlier. For now, however, widespread use of hydrogen as fuel is purely theoretical.

Research into the use of hydrogen as a fuel got a boost when President George W. Bush announced a hydrogen fuel initiative in his 2003 State of the Union address. By the end of 2004, the Department of Energy had awarded $75 million in research grants in support of this initiative.

FUTURE TRENDS IN U.S. RENEWABLE ENERGY USE

In Annual Energy Outlook 2004, the EIA forecasted that total renewable fuel consumption, including ethanol for transportation, will increase by 1.9% per year from 2002 to 2025. About 60% of the projected demand for renewable fuel in 2025 will be for electricity generation. In 2002 renewable energy provided 5.8 quadrillion Btu, which is projected to increase to 9 quadrillion Btu in 2025. Renewable fuel is expected to remain a small contributor to overall electricity generation, rising only from 9% of the total generation in 2002 to 9.1% in 2025.

Hydropower production is projected to rise only slightly from 260 billion kilowatt-hours in 2002 to 309 billion kilowatt-hours in 2025. The production of other renewables should increase steadily. (See Figure 6.10.) For example, significant increases are projected for both geothermal energy and wind power capacity from 2002 to 2025. The EIA projected that wind power will increase from 4.8 gigawatts in 2002, to 8 gigawatts in 2010, and 16 gigawatts in 2025. The EIA projected that high-output geothermal capacity will increase from 13 billion kilowatt-hours in 2002 to 47 billion in 2025. This, however, will provide less than 1% of the nation's electricity needs.

Municipal solid waste and landfill gas energy production is expected to increase by nine billion kilowatthours from 2002 to 2025. The largest source of renewable generation (not including hydropower) is biomass, which is projected to more than double from 2002 to 2025. (See Figure 6.11.) Solar energy is not expected to contribute much to centrally generated electricity.

FIGURE 6.10

FIGURE 6.11