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Renewable Energy

CHAPTER 10
RENEWABLE ENERGY

WHAT IS RENEWABLE ENERGY?

Imagine an energy source that uses no oil, produces no pollution, cannot be affected by political events and cartels, creates no radioactive waste, and yet is economical. Although that might sound impossible, some experts claim that technological advances could make a renewable energy-based economy achievable by the mid-twenty-first century.

Renewable energy is a term used to describe energy from sources that are naturally regenerated and are, therefore, virtually unlimited. These energy sources include the sun, wind, water, vegetation, and the heat of the earth.

Solar energy, wind energy, hydropower, and geothermal power are all renewable 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 someday provide a substantially better energy source than conventional, fossil fuel burning methods. As the United States and the rest of the world continue to expand their energy needs, which puts a strain on the environment, alternative sources of energy continue to be explored in the hope that they might provide a higher percentage of America's (and the world's) future energy requirements.

A HISTORICAL PERSPECTIVE

Before the nineteenth century most energy used 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 1800s with the Industrial Revolution, a period marked by the rise of factories—first in Europe and then in North America. Coal was the most efficient fuel for the steam engine, which was perhaps the most important invention of the Industrial Revolution. By the turn of the twentieth century, coal had replaced wood as the main fuel source.

Coal's dominance, however, lasted only a few decades. In the early 1950s petroleum products such as gasoline and diesel fuel surpassed coal as the fuel of choice. (See Figure 10.1.) 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 percent 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 brought on by political events in the Middle East made Americans more aware of the importance of developing alternative sources of energy to supplement and perhaps even replace fossil fuels. In major cities throughout the United States, gasoline rationing became commonplace, lower thermostat settings for offices and living quarters were encouraged, and people waited in line to fill their gas tanks. The crisis was over by the late 1970s and oil prices dropped, but the incident shocked America, where mobility and personal transportation are highly valued. As a result, President Jimmy Carter's administration 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 producers from state and federal utility regulations and required existing local utilities to buy electricity from the smaller producers. PURPA encouraged the growth of small-scale electric power plants, especially those fueled by renewable sources. The renewable industries responded by growing rapidly, gaining experience, improving technologies, and lowering costs. This act was a major 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 best. 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) continues to support some research and development to explore alternate sources of energy. Table 10.1 shows a detailed breakdown of the nation's energy sources between 1949 and 2002. Renewable energy comprised 9 percent of the total in 1949.

How Much of Today's Energy Is Renewable?

In 2003 renewable energy accounted for only 6 percent of total U.S. energy consumption. (See Figure 10.2.) Of that hydroelectric power accounted for 44 percent, followed by wood (34 percent) and waste (10 percent). Geothermal energy sources, alcohol fuels, and wind and solar power were minor sources. (See Figure 10.3.)

Figure 10.4 shows the historical contributions of hydroelectric power, wood, and waste to renewable energy resources since 1973. Consumption of hydroelectric and wood power has varied up and down over time, while waste shows a gradual upward trend.

Electric utility companies have historically been the biggest consumers of renewable energy because they use it to generate electricity. In 2003 electric power generation accounted for 59 percent of renewable energy consumption. It was followed by industrial uses with 30 percent of the total. Consumption by residential, commercial, and transportation sectors was minor. Industrial use has outpaced residential use since the late 1950s.

BIOENERGY

The term bioenergy refers to energy that is generated using biomass—organic material such as wood, agricultural waste from plants and animals, seaweed and algae, and municipal solid waste (MSW) or garbage. These raw materials can be converted into liquid or gaseous biofuels or used directly to provide heat, electricity, or combined heat and power. Figure 10.5 shows common materials used to make bioenergy. The by-products of biomass conversion can be used for fertilizers and chemicals.

Bioenergy from wood, waste, and alcohol fuels accounted for an estimated 2.9 quadrillion British thermal

Fossil fuels Renewable energy1
Year Coal Natural gas (dry) Crude oil2 Natural gas plant liquids Total Nuclear electric power Hydroelectric pumped storage3 Conventional hydroelectric power Wood, waste, alcohol4 Geothermal Solar Wind Total Total
194911.9745.37710.6830.71428.748051.4251.549NANANA2.97431.722
195014.0606.23311.4470.82332.563051.4151.562NANANA2.97835.540
195114.4197.41613.0370.92035.792051.4241.535NANANA2.95838.751
195212.7347.96413.2810.99834.977051.4661.474NANANA2.94037.917
195312.2788.33913.6711.06235.349051.4131.419NANANA2.83138.181
195410.5428.68213.4271.11333.764051.3601.394NANANA2.75436.518
195512.3709.34514.4101.24037.364051.3601.424NANANA2.78440.148
195613.30610.00215.1801.28339.771051.4351.416NANANA2.85142.622
195713.06110.60515.1781.28940.133(s)51.5161.334NANANA2.84942.983
195810.78310.94214.2041.28737.2160.00251.5921.323NANANA2.91540.133
195910.77811.95214.9331.38339.0450.00251.5481.353NANANA2.90141.949
196010.81712.65614.9351.46139.8690.00651.6081.3200.001NANA2.92942.804
196110.44713.10515.2061.54940.3070.02051.6561.2950.002NANA2.95343.280
196210.90113.71715.5221.59341.7320.02651.8161.3000.002NANA3.11944.877
196311.84914.51315.9661.70944.0370.03851.7711.3230.004NANA3.09847.174
196412.52415.29816.1641.80345.7890.04051.8861.3370.005NANA3.22849.056
196513.05515.77516.5211.88347.2350.04352.0591.3350.004NANA3.39850.676
196613.46817.01117.5611.99650.0350.06452.0621.3690.004NANA3.43553.534
196713.82517.94318.6512.17752.5970.08852.3471.3400.007NANA3.69456.379
196813.60919.06819.3082.32154.3060.14252.3491.4190.009NANA3.77858.225
196913.86320.44619.5562.42056.2860.15452.6481.4400.013NANA4.10260.541
197014.60721.66620.4012.51259.1860.23952.6341.4310.011NANA4.07663.501
197113.18622.28020.0332.54458.0420.41352.8241.4320.012NANA4.26862.723
197214.09222.20820.0412.59858.9380.58452.8641.5030.031NANA4.39863.920
197313.99222.18719.4932.56958.2410.91052.8611.5290.043NANA4.43363.585
197414.07421.21018.5752.47156.3311.27253.1771.5400.053NANA4.76962.372
197514.98919.64017.7292.37454.7331.90053.1551.4990.070NANA4.72361.357
197615.65419.48017.2622.32754.7232.11152.9761.7130.078NANA4.76861.602
197715.75519.56517.4542.32755.1012.70252.3331.8380.077NANA4.24962.052
197814.91019.48518.4342.24555.0743.02452.9372.0380.064NANA5.03963.137
197917.54020.07618.1042.28658.0062.77652.9312.1520.084NANA5.16665.948
198018.59819.90818.2492.25459.0082.73952.9002.4850.110NANA5.49467.241
198118.37719.69918.1462.30758.5293.00852.7582.5900.123NANA5.47167.007
198218.63918.31918.3092.19157.4583.13153.2662.6150.105NANA5.98566.574
198317.24716.59318.3922.18454.4163.20353.5272.8310.129NA(s)6.48864.106
198419.71918.00818.8482.27458.8493.55353.3862.8800.165(s)(s)6.43168.832
198519.32516.98018.9922.24157.5394.07652.9702.8640.198(s)(s)6.03367.647
198619.50916.54118.3762.14956.5754.38053.0712.8410.219(s)(s)6.13267.087
198720.14117.13617.6752.21557.1674.75452.6352.8230.229(s)(s)5.68767.608
198820.73817.59917.2792.26057.8755.58752.3342.9370.217(s)(s)5.48968.951
198921.34617.84716.1172.15857.4685.6025R2.8373.062R0.3170.055R0.022R6.294R69.364
199022.456R18.32615.5712.175R58.5296.1040.036R3.046R2.662R0.3360.060R0.029R6.133R70.729
199121.59418.22915.7012.30657.8296.4220.047R3.0162.702R0.3460.063R0.031R6.158R70.362
199221.62918.37515.2232.36357.5906.4790.0432.6172.8470.3490.0640.0305.90769.933
199320.24918.58414.4942.40855.7366.4100.0422.8922.8040.3640.0660.0316.15768.262
Fossil fuels Renewable energy1
Year Coal Natural gas (dry) Crude oil2 Natural gas plant liquids Total Nuclear electric power Hydroelectric pumped storage3 Conventional hydroelectric power Wood, waste, alcohol4 Geothermal Solar Wind Total Total
199422.11119.34814.1032.39157.9526.6940.0352.6832.9390.3380.0690.0366.06570.676
199522.029R19.08213.8872.442R57.4407.0750.0283.2053.0680.2940.0700.0336.669R71.156
199622.684R19.34413.7232.530R58.2817.0870.0323.5903.1270.3160.0710.0337.137R72.472
199723.21119.39413.6582.49558.7586.5970.0413.6403.0060.3250.0700.0347.07572.389
199823.93519.61313.2352.42059.2047.0680.0463.2972.8350.3280.0700.0316.56172.787
199923.18619.34112.4512.52857.5057.6100.0623.268R2.8850.3310.0690.046R6.599R71.652
200022.623R19.66212.3582.611R57.2547.8620.0572.811R2.9070.3170.0660.057R6.158R71.218
2001R23.053R20.22712.282R2.547R58.1098.0280.090R2.201R2.678R0.311R0.065R0.068R5.324R71.372
2002P22.55419.56112.3142.56156.9908.1450.0892.6682.7560.3040.0640.1065.89970.946
1End-use consumption and electricity net generation.
2Includes lease condensate.
3Pumped storage facility production minus energy used for pumping.
4Alcohol is ethanol blended into motor gasoline.
5Included in "Conventional Hydroelectric Power."
R = Revised. P = Preliminary. NA = Not available. (s) = Less than 0.0005 quadrillion Btu.
Note: Totals may not equal sum of components due to independent rounding.
source: "Table 1.2. Energy Production by Source, 1949–2002," in Annual Energy Review 2002, U.S. Department of Energy, Energy Information Administration, Washington, DC, October 2003

units (Btu) of energy in 2003, comprising 47 percent of renewable energy consumed. (See Figure 10.3.)

Biomass Conversion

There are two types of biomass conversion processes: thermochemical conversion and biochemical conversion. Thermochemical conversion uses heat to produce chemical reactions in biomass. Direct combustion is the easiest and most commonly used method. Materials such as dry wood or agricultural wastes are chopped and burned to produce steam, electricity, or heat for industries, utilities, and homes. Wood burning in stoves and fireplaces is one example. The burning of agricultural wastes is also becoming more widespread. In Florida, for example, sugar cane producers use the residue from the cane to generate much of their energy.

Pyrolysis, also called gasification or carbonization, uses heat to break down biomass to yield liquid, gaseous, and solid fuels. Converting wood to charcoal is an example of this process.

The second type of conversion process, 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 (without oxygen) 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. The DOE estimates that many thousands of biofuel plants are in use in Korea, and perhaps half a million plants operate in China.

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

Wood

Wood energy was the first energy source in America's industrialization. Wood, the most commonly used biofuel, is still used to heat millions of homes every year. In 2003 it provided 2.1 quadrillion Btu, accounting for 34 percent of renewable energy consumption (See Figure 10.3.)

When wood is widely used as a fuel in an area, deforestation can occur, resulting in the possibility of soil erosion and mud slides. Burning wood, as with the burning of fossil fuels, also pollutes the environment.

Ethanol and Methanol—Important Agricultural By-Products

Ethanol is a colorless, nearly odorless, flammable liquid derived from fermenting plant material that contains carbohydrates in the form of sugar. U.S. ethanol production has grown steadily since 1980, reaching 2.81 billion gallons in 2003, according to the U.S. Department of Energy. Production capacity is largely located in the farming regions of the upper Midwest. (See Figure 10.6.)

Most of the ethanol manufactured for use as fuel is derived from corn, wood, and sugar. A mixture of 10 percent ethanol and 90 percent gasoline is usable in any internal combustion engine without the need to modify the motor. Although the DOE claims that the demand for alcohol/gasoline blends is increasing because alcohol can substitute for lead as an octane booster, there is little question that the development of ethanol depends more on the continued support of farm state legislators than any economic benefit.

Ethanol is difficult and expensive to produce in bulk. Methanol-blend fuels have also been tested successfully. (Methanol is methyl alcohol.) Using methanol instead of diesel fuel virtually eliminates sulfur emissions and reduces other environmental pollutants usually emitted from trucks and buses. Burning biofuels in vehicle engines creates a "carbon cycle" in which the earth's vegetation can in turn make use of the products of combustion and, therefore, reduce net greenhouse gases. (See Figure 10.7.) Producing methanol from biofuels, however, is costly.

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 sugar cane. Worldwide, there are enough corncobs and rice hulls left over from annual crop production to produce more than 40 billion gallons of ethanol.

Advocates of wood-derived ethanol believe that the eventual result of wood-to-ethanol conversion research could create 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 and, in the meantime, contribute to the prevention of global warming by continuing their carbon dioxide processing function. Other scientists warn that a huge demand for transportation fuels could create a demand for wood that might accelerate the destruction of old-growth forests and endanger ecosystems. Without careful attention to forestry practices, ethanol production might aggravate rather than solve the fuel problem.

Municipal Solid Waste

Each year millions of tons of municipal solid waste (MSW), or garbage as it is commonly called, are buried in landfills and city dumps. This method of disposal is not only costly but is becoming increasingly difficult as some landfills across the nation are near capacity. Many communities have discovered that they can solve two problems at once by constructing waste-to-energy (WTE) plants. Not only is garbage burned and reduced in volume by 90 percent, energy in the form of steam or electricity is generated in a cost-effective way. The potential energy benefit is significant.

WASTE-TO-ENERGY PLANTS.

The two most common WTE plant designs are the mass burn (also called direct combustion) and the refuse derived fuel (RDF) systems.

Most WTE 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.

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 garbage produces heat, and that heat is used to produce steam. The steam can be used directly for industrial needs or heat can be sent through a turbine to power a generator to produce electricity.

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, 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.

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

LANDFILL GAS RECOVERY.

Landfills contain a large amount of biodegradable matter. Gas is created because of the lack of oxygen that helps the growth of methagens—types of bacteria that produce methane gas and carbon dioxide. In the past, as landfills aged, these gases built up and leaked out. This gas leakage prompted some communities to drill holes and burn off the flammable and dangerous methane.

The energy crisis of the 1970s made this 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. Depending on the extraction rates, most existing sites can produce gas for about 20 years.

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 burned to produce electricity. In its purest form methane gas is equivalent to natural gas and can be used in exactly the same way.

The advantages of tapping gas from a landfill go beyond the energy provided by the methane. When internal pressure forces methane gas to seep into the air, it carries very unpleasant odors into the surrounding neighborhoods. The released methane can also be a danger because, if it accumulates and is accidentally ignited, it can explode. Extracting the methane gas for energy eliminates both of these problems.

HYDROPOWER

Hydropower is the energy that comes from the natural flow of water. Usually, the power is harnessed by taking advantage of gravity when water falls from one level to another. The energy of falling water is converted into mechanical energy. In the past, water's energy was harnessed by waterwheels to grind grain or turn saws. Modern technology uses water's energy to turn turbines that create electricity. Hydropower is a renewable, nonpolluting, and reliable energy source.

Hydropower is still 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 flow of water from the dam pushes the turbine blades that turn the rotor part of the electric generator. When the coils of wire on the rotor sweep past the generator's stationary coil, electricity is produced. Whenever power is needed at peak times, water valves are opened and, in a short amount of time, turbine generators produce extra power. The Hoover Dam, located on the Colorado River at the Nevada-Arizona border, is the site of one of the largest U.S. hydroelectric plants.

According to the Energy Information Administration's March 2004 Monthly Energy Review, in 2003 hydroelectric power generated about 2.8 quadrillion Btu of energy in the United States, down substantially from when it peaked at 3.64 billion quadrillion Btu in 1997. (See Table 10.1.) Hydropower accounted for 44 percent of the nation's renewable energy consumption in 2003.

Advantages and Disadvantages of Hydropower

Small hydropower plants in the United States are costly to build but quickly 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, a problem especially during years with drought conditions. Other concerns include the difficult search for the proper terrain on which to build a hydroelectric power plant; the high cost of construction; and the ecological concern that dams could ruin streams, dry up waterfalls, and interfere with marine life habitats.

Large hydropower plants suffer from the same problems except that they rarely lack sufficient water since they can be built only on very large rivers. There is little potential to build new, large, hydropower plants in the United States because plants have already been built at all of the best sites.

New Directions in Hydropower Energy

Since almost all power sites have already been developed, hydropower's contribution to U.S. energy generation should remain relatively constant—although existing sites can become more efficient as new generators are added.

Most of the new development in hydropower is occurring in developing nations that see it as an effective method of supplying power to their growing populations. Major hydropower development programs are tremendous public works projects requiring huge amounts of money, most of it borrowed from the developed world. Leaders of developing countries believe that, in the long run, despite threats to the environment, the dams will pay for themselves by bringing cheap electric power to their people.

While developing nations have utilized only a small portion of their large-scale hydropower potential, the United States and Europe have developed a major proportion of their potential. In addition, dams are now less favored because of their harm to the environment. Largescale hydropower development has virtually stopped in the United States, with not one new dam being approved for federal funding since the late 1980s.

Dams in the United States were usually constructed entirely with federal monies. Since 1986, however, any new dam proposed in the United States must receive half its funding from local governments. Any new major supplies of hydroelectric power for the United States will most likely come from Canada.

Other Alternatives Using Water

The potential power locked in the world's oceans is unknown. However, since 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.

TIDES AND WAVES.

A tidal plant uses the power generated by the tidal flow of water as it ebbs (flows back out to sea). A minimum tidal range of three to five yards is generally considered necessary for an economically feasible plant. Canada, for example, has built a 20-megawatt unit at the Bay of Fundy, where the tidal range—15 yards—is the largest in the world. The largest existing tidal facility is the 240-megawatt plant at the La Rance estuary in northern France.

In 2000 the world's first commercial wave power station became operational on the island of Islay in Scotland. The small system is called a Limpet, short for land-installed marine powered energy transformer. The Limpet supplies up to 500 kilowatts of electricity to the island's electrical power grid. Several projects are underway in Japan and the Pacific region to determine a way to use the potential of the huge waves of the Pacific.

OCEAN THERMAL ENERGY CONVERSION.

In 1881 Jacques Arsene d'Arsonval, a French physicist, was the first to propose tapping the thermal energy of the ocean. Not until 1974, however, was a laboratory and test facility for ocean thermal energy conversion (OTEC) technologies built at the National Energy Laboratory of Hawaii. In 1980 the DOE built OTEC-1, a test site on board a converted U.S. Navy tanker. In 1980 Congress enacted two laws to promote the commercial development of OTEC technology—the Ocean Thermal Energy Conversion Act (PL 96-320) later modified by PL 98-623, and the Ocean Thermal Energy Conversion, Research, and Development and Demonstration Act (PL 96-310).

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 generate electricity. OTEC systems can be installed on ships, barges, or offshore platforms with underwater cables that transmit electricity to shore. In addition to providing power, OTEC systems can be used to desalinate water, provide air conditioning and refrigeration, and produce methanol, ammonia, hydrogen, aluminum, chlorine, and other chemicals.

GEOTHERMAL ENERGY

Since ancient times humans have exploited the earth's natural hot water sources. Although bubbling hot springs became public baths in ancient Rome, using naturally occurring hot water and underground steams to produce power is a relatively modern development. The first electricity to be generated from natural steam was in Italy in 1904. The world's first natural steam power plant was built in 1958 in a volcanic region of New Zealand. A field of 28 geothermal power plants covering 30 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 within the ground. Only a fraction of this vast storehouse of energy can be extracted, usually where there are 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 10.8.) 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 turbines is then fed into a utility grid and distributed to residential and commercial customers. By the late 1990s electricity from this source accounted for almost two-thirds of the world's geothermal energy use.

Types of Geothermal Energy

Like most natural energy sources, geothermal energy is usable only when it is concentrated in one spot, in what is called a "thermal reservoir." The four basic categories of thermal reservoirs are hydrothermal (dry steam and hot, or wet, steam), dry rock, geopressurized, and magma (rock so hot it has liquefied) reservoirs. Most of the known areas for geothermal power in the United States are located west of the Mississippi River. (See Figure 10.9.)

Hydrothermal reservoirs consist of a heat source covered by a permeable formation through which water circulates. Dry 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 then piped directly to the electrical generating station. These systems are the cheapest and simplest form of geothermal energy.

Hot steam systems are created when underground water is heated to more than 700 degrees Fahrenheit by the surrounding hot rock or magma, but the water remains liquid because of intense pressure. When the water is brought to the surface and the pressure is reduced, a small amount of water becomes steam that is then separated and used to power an electrical generating plant.

Dry rock formations are the most common geothermal source, especially in the west. To tap this source of energy, water is injected into naturally hot rock formations to produce steam or water for collection.

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

Magma resources are found where molten or partially liquefied rock is located from 10,000 to 33,000 feet below the earth's surface. Because magma is so hot, ranging from 1,650 degrees to 2,200 degrees Fahrenheit, it is a good geothermal resource. The process for extracting energy from magma is still in the experimental stages.

Disadvantages of Geothermal Energy

Geothermal plants are expensive because they must be built near the source. Other drawbacks include low efficiency, bad odors from sulfur released in processing, noise, lack of access for most states, and potentially harmful pollutants (hydrogen sulfide, ammonia, and radon). Also, poisonous arsenic or boron are often found in geothermal waters. Serious environmental concerns have been raised over the release of chemical compounds, potential water contamination, the collapse of land surface around the area from which the water is being drained, and potential water shortages resulting from massive withdrawals of water.

American Production of Geothermal Energy

Geothermal energy ranked fourth in U.S. renewable energy production in 2003 after hydroelectric, wood, and waste energy. Geothermal energy accounted for 0.3 quadrillion Btu in 2003, down from the early 1990s when it approached 0.4 quadrillion Btu. In 2003 it represented only 5 percent of renewable energy consumed in the United States.

Public-sector involvement in the geothermal industry began with the passage of the Geothermal Steam Act of 1970 (PL 91-581), which authorized the U.S. Department of the Interior to lease geothermal resources on federal lands. Although the United States is the greatest producer of geothermal power with 28 percent of the world's capacity, the geothermal industry in the United States is losing steam. Oil prices have remained relatively low, and most of the easily exploited geothermal reserves have already been developed. In addition, utility companies and independent power producers argue over who should build additional generating capacity and what prices should be paid for the power. As a result, U.S. geothermal capacity has dropped. 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.

World Production of Geothermal Energy

During the oil crisis of the 1970s, when energy was at the forefront of the international agenda, governments scrambled to find domestic alternatives to imported oil. As public interest grew, research dollars became available and a large number of geothermal energy plants were built. Although interest has since faded, geothermal power's commercial development worldwide has continued at a slow but steady pace.

Since 1979 worldwide geothermal electrical generating capacity has nearly tripled. According to the International Geothermal Association, there were nearly 8,000 megawatts of installed capacity in 2000. The U.S. accounted for 28 percent of the total, followed by the Philippines (24 percent), Italy (10 percent), Mexico (9 percent), and Indonesia and Japan (7 percent each). Together these countries accounted for 85 percent of total capacity.

Worldwide geothermal capacity is still less than that of a handful of average-sized coal-fired power plants. World geothermal reserves are immense but unevenly distributed. These reserves fall mostly in seismically active areas at the margins or borders of Earth's nine major tectonic plates. Exploited reserves represent only a small fraction of the overall potential—many countries are believed to have in excess of 100,000 megawatts of geo-thermal energy available.

A few nations in the developing world—El Salvador, Kenya, Bolivia, Costa Rica, Ethiopia, India, and Thailand—have considerable steam reserves available for power generation. Debt-ridden developing nations that have substantial unexploited geothermal reserves are especially eager to use them instead of relying on costly fossil fuel imports for their energy needs.

WIND ENERGY

Wind energy is really a form of solar 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. As a result, winds are strongly influenced by local terrain, water bodies, weather patterns, vegetation, and other factors. This wind flow, when "harvested" by wind turbines, can be used to generate electricity.

Wind machines have changed dramatically from those that were common in the 1800s. Early windmills produced mechanical energy to pump water and run 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, state-of-the-art wind turbines look more like airplane propellers. Their sleek, high-tech aerodynamics and fiber-glass design allow them to generate an abundance of electricity, while they also produce mechanical energy and heat. (See Figure 10.10.)

Unlike solar energy systems, wind systems produce renewable energy at night as well as during the day. During the 1990s industrial and developing countries alike began using wind power as an adaptable source of electricity to complement their 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, particularly 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 in much of Europe and Asia. Denmark, the Netherlands, China, and India are especially interested in fostering the development of domestic wind industries. In the United States it is estimated that sufficient wind energy is available to provide more than one trillion kilowatt-hours of electricity annually.

Energy Production by Wind Turbines

Wind is the world's fastest growing energy source. According to the American Wind Energy Association, worldwide capacity at the end of 2003 was approximately 39,000 megawatts, up 26 percent from the year before. Europe generated almost three-quarters of the world's wind power. U.S. capacity at the end of 2003 was 6,374 megawatts, accounting for 16 percent of the total. Nearly 1,700 of those megawatts were added during 2003.

The wind industry in the United States began with research projects in California. In 1981 the state erected 144 relatively small turbines capable of generating a combined total of 7 megawatts of electricity. Within a year the number of turbines had increased ten times, and by 1986 had multiplied 100-fold. The 1980s saw an explosion of wind technology in California. By 1995 the state produced enough wind power to supply all of San Francisco's residents. Experts point out that California's dominance had less to do with wind availability than tax credits that were offered by the state until 1999. Approximately 32 percent of the total 6,374 megawatts of installed wind power capacity in the United States was located in California at the end of 2003. (See Figure 10.11.)

During the 1990s wind energy facilities began to appear in other states, particularly in the Midwest. Texas now supplies 20 percent of the nation's wind power capacity, thanks to legislative policies that require the state's utilities to provide renewable generating capacity. Together, California and Texas generate more than half of the country's wind power.

Studies show that several states, especially the plains states, have wind speeds sufficient to supply electricity. Twelve states—North Dakota, South Dakota, Texas, Kansas, Montana, Nebraska, Wyoming, Oklahoma, Minnesota, Iowa, Colorado, and New Mexico—contain 90 percent of the U.S. wind energy potential. Refinements in wind turbine technology may enable a substantial portion of the nation's electricity to be produced by wind energy.

Problems in the U.S. Wind Industry

Wind energy capacity grew very slowly until the late 1990s, adding less than 300 megawatts of capacity between 1990 and 1998. Crude oil prices fell during this time, making oil and gas the lowest-cost fuel sources. Concern about reducing the federal budget resulted in a change in federal policy toward renewable energies. Furthermore, some people were concerned about the uncertainty involving electric utility deregulation. U.S. producers received around $.03 to $.04 per kilowatt-hour in price guarantees while wind producers in Germany, Denmark, and India were guaranteed more than twice that amount. As a result investors often found investing in wind energy in the United States too risky. However, the tide began to turn in the late 1990s. Between 1999 and 2003 the country's wind generating capacity expanded at an average rate of 28 percent annually.

Development of Wind Energy throughout the World

During the decade following the 1973 oil crisis, more than 10,000 wind machines were installed worldwide, ranging in size from portable units to multi-megawatt turbines. In developing villages small wind turbines recharge batteries and provide essential services. In China small wind turbines allow people to watch their favorite television shows, a major reason for the increased demand for turbines in China.

Although wind power supplies less than 0.1 percent of the world's electricity, it is one of the fastest growing energy sources. The most ambitious wind energy program is planned for India, which expects to provide enough electrical power to serve 5 million customers. India is expected to be the most rapidly growing market for wind turbines and, if the planned program is successful, wind may supply more energy for India than the country's nuclear program.

Interest in wind energy has been driven in part by the declining cost of capturing wind energy—from more than $.25 per kilowatt-hour in 1980 to $.05 per kilowatt-hour for new turbines in the late 1990s. This makes wind power nearly competitive with gas- and coal-powered plants, even before considering wind's environmental advantages.

Encouraged by improved technology, falling costs, and government incentives like tax credits and guaranteed prices, wind power is booming across Europe. One reason for the growth in the industry is that the European Union wants to diversify its energy sources while clamping down on pollution. Almost no country supports the expansion of nuclear power and, in many areas, wind power is becoming economically viable.

Wind energy is produced under entirely different circumstances in the United States than in Europe. American entrepreneurs, seeing wind energy as a potentially profitable business, built large wind farms with huge numbers of turbines. When oil prices fell and tax credits were cut, growth stalled. In Denmark, Germany, Sweden, and the Netherlands, wind energy began as a grassroots movement, with small groups of politically motivated investors installing one or a few machines at a time. In Spain, Britain, and Greece, the clusters were larger because money was provided by local governments and utilities. The latest trend in Europe is to build wind farms offshore where there is more wind and fewer complaints that they clutter the landscape.

Advantages and Disadvantages of Using 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. Some environmentalists have charged that the wind turbines are responsible for the loss of some species of endangered birds that fly into the blades. Finally, as with all types of renewable energy, wind power is more expensive to produce than energy generated through conventional means, at least when the price of oil remains low.

On the other hand, 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 semiarid and arid regions. Wind farming also offers the added benefit of reducing soil loss on land prone to wind erosion because turbines capture the wind and decrease its potential for downwind destruction.

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 generates neither pollution nor hazardous waste. Solar-powered cars have already 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, the Massachusetts Institute of Technology built the first solar-powered house in 1939.

Solar radiation is nearly constant outside Earth's atmosphere, but the amount of solar energy, or insolation, reaching any point on Earth varies with changing atmospheric conditions such as clouds and dust, and the changing position of Earth relative to the sun. In the United States insolation is greatest in the West and Southwest. Nevertheless, almost all U.S. regions could use solar energy.

Passive and Active Solar Energy Collection Systems

Passive solar systems such as greenhouses, or windows with a southern exposure, use heat flow, evaporation, or other natural processes to collect and transfer heat. They are considered the least costly and least difficult systems to implement. (See Figure 10.12.)

Active solar systems use mechanical methods to control the energy process. 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 (solar panel or collector) 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. (See Figure 10.12.) 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 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 (energy) is transferred to the water that, in turn, powers a steam-driven electric generator. In a distributed solar thermal system, the collected energy powers irrigation pumps, provides electricity for small communities, or captures 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 migrates to the bottom and absorbs the heat, while 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 usually last up to 20 years. PV cells are commonly used to power small devices such as watches or calculators. They are also used on a larger scale to provide electricity for rural households, recreational vehicles, and businesses. Solar panels using PV cells have generated electricity for space stations and satellites for many years. Solar panels have also provided electricity for a few major buildings in the United States.

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

The use of PV technology is expanding both in the United States and abroad. Although PV systems have a higher initial cost than conventional power plants, they have a much lower operating cost.

Using Solar Energy

Because it is difficult to measure solar energy directly, other measures are often used as an indicator. According to the DOE there were 84 low-temperature collector manufacturers in 1979. That number dropped to ten by 2001. (See Figure 10.13.) Total shipments of solar thermal collectors peaked in 1981 at more than 21 million square feet and declined sharply after that. According to the DOE's Annual Energy Review 2002 (Washington, DC, 2003), since 1991 there has been a steady increase in shipments, including a sharp spike in 2001 up to 11 million square feet.

By 1999 the market for solar thermal collectors for space heating had virtually disappeared. However, solar energy became increasingly popular as a means for heating swimming pools and water used in the home. Most of the solar thermal collector market is driven by this residential demand (primarily in the Sunbelt states), with only a small proportion for commercial purposes. Some state and municipal power companies have added solar systems as adjuncts to their regular power sources during peak hours.

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. Very few areas of the United States have enough constant sunshine to make this system an efficient replacement for conventional methods. In addition, a large amount of land area is necessary for the most efficient collection of solar energy for solar thermal units.

PV cell solar energy systems are probably the most attractive form of solar energy production. A PV cell system is nonpolluting, silent, and can be operated by computer. In addition, it is less expensive to operate because there are no turbines or other moving parts, which makes maintenance minimal. Above all the fuel source (sunshine) is free and plentiful. The disadvantage of a PV cell energy system is the initial cost. As shown in Figure 10.14 total shipments by PV cells increased dramatically over the last decade, reaching 98 thousand peak kilowatts during 2001.

Future Development Trends

Interest in PV cell 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. This use will most likely increase where the traditional use of an electrical cord is a problem.

Although solar power still costs more than fossil fuel energy, utilities could turn to solar energy to provide extra power on extremely hot or cold days. Some people believe that building solar energy systems to provide peak power capacity would be cheaper in the long run than building new and expensive diesel fuel generators, utility regulators may decide that the price of fossil fuel power must include the hidden cost of fossil fuel damage to the environment caused by acid rain and the greenhouse effect.

HYDROGEN—A FUEL OF THE FUTURE?

Hydrogen is the lightest and most abundant chemical element. It contains only one proton and one electron. From an environmental point of view it is also the ideal fuel. Its combustion as a fuel or conversion to electricity produces only water vapor—it is entirely carbon-free. The National Aeronautics and Space Administration (NASA) has used liquid hydrogen for decades to power rockets into space.

Three-quarters of the mass of the universe consists of hydrogen; however, it is combined with other elements, as in water. The elemental, combustible, form of hydrogen is not found in the atmosphere. Hydrogen-containing compounds cannot be converted into pure gas hydrogen without the expenditure of energy. Most elemental hydrogen is currently obtained by separating it from hydrocarbons, such as natural gas, gasoline, or methanol. This process is called "reforming." However, reforming requires energy in the form of heat. Therefore, with today's technology little or nothing can be gained from an overall energy point of view.

Hydrogen has considerable potential as a clean fuel and, because it is a gas, can be distributed with essentially the same technology as natural gas. Scientists are researching ways to economically produce hydrogen gas. The possibility of a transition to hydrogen has been considered for more than a century, and many see hydrogen as the logical "third-wave" fuel—hydrogen gas following oil, just as oil replaced coal decades earlier.

The most promising application of hydrogen is in fuel cells. A fuel cell works like a battery, except it never runs down as long as hydrogen is supplied. It contains two electrodes—a negative electrode or anode and a positive electrode or cathode—surrounding an electrolyte. An electrolyte is a substance that can conduct electricity. Hydrogen is fed to the anode, and the atoms are separated into protons and electrons that travel along different paths to the cathode. The electrons travel along an external circuit creating an electricity flow. The protons travel through the electrolyte to the cathode, where oxygen is fed in. The protons mix with the oxygen atoms and electrons, forming water and generating heat.

Research in the United States is focused on the use of traditional hydrocarbon fuels (like gasoline) as the hydrogen source for vehicles containing a fuel "reformer" and a fuel cell. This takes advantage of the existing infrastructure of gasoline stations.

In March 2004 the DOE introduced its "Hydrogen Posture Plan," which outlines a plan to create a hydrogen-based transportation energy system in the United States. President Bush requested that $227 million be spent on research in 2005 to support this hydrogen fuel initiative.

THE FUTURE OF RENEWABLE ENERGY

Renewable energy accounted for 8 percent of the total world energy production in 2001. (See Figure 10.15.) Global energy consumption is expected to increase by 60 percent through the next two decades, reaching 600 quadrillion Btu by 2020. Most of the growth will be in developing countries, particularly in Asia.

In 2003 renewable energy contributed only 6 percent of the total energy consumed by the United States. The nation's fleet of automobiles has become less energy efficient, and consumers are less interested in energy-saving technology. Many economists believe that only a return of higher energy prices will cause Americans to once again reduce their energy use and consider renewable energy sources. Despite their environmental advantage over fossil fuels, renewable energies have never attracted enough financial support from the government, the public, or energy companies to the point that they can be cost competitive with fossil fuel power.

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