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Chapter 5. Building the Solar/Hydrogen Economy: Tapping the Earth’s Heat
In contrast to other sources of renewable energy, such as wind power, solar cells, and hydropower, which rely directly or indirectly on sunlight, geothermal energy comes from within the earth itself. Produced radioactively within the earth and by the pressures of gravity, it is a vast resource, most of which is deep within the earth. Geothermal energy can be economically tapped when it is relatively close to the surface, as evidenced by hot springs, geysers, and volcanic activity.
This energy source is essentially inexhaustible. Hot baths, for example, have been used for millennia. It is possible to extract heat faster than it is generated at any local site, but this is a matter of adjusting the extraction of heat to the amount generated. In contrast to oil fields, which are eventually depleted, properly managed geothermal fields keep producing indefinitely.
Geothermal energy is much more abundant in some parts of the world than in others. The richest region is the vast Pacific Rim. In the East Pacific, geothermal resources are found along the coastal regions of Latin America, Central America, and North America all the way to Alaska. On the west side, they are widely distributed in Eastern Russia, Japan, the Korean Peninsula, China, and island countries such as the Philippines, Indonesia, New Guinea, Australia, and New Zealand.47
This buried energy source is used directly both to supply heat and to generate electricity. When used for heat, hot water or steam is typically pumped from underground, heat is extracted, and then the water is re-injected into the earth. Electricity can be generated from hot water pumped from beneath the earth's surface, from steam extracted directly, or from steam produced by circulating water into fissures in hot rock below the surface. Geothermal energy extracted directly can be used for space heating, as in Iceland, where it heats some 85 percent of buildings; for hot baths where springs bring geothermal energy to the surface, as in Japan; and for generating electricity, as in the United States.48
First harnessed for electricity generation in Italy in 1904, geothermal energy is now used in scores of countries, although in many cases it is used primarily to supply hot water to bath houses. During the first seven decades of the twentieth century, the growth in geothermal electrical generating capacity was modest, reaching only 1,100 megawatts in 1973. With the two oil price hikes in 1973 and 1979, however, use of geothermal energy began to grow. By 1998, it had expanded nearly eightfold, to 8,240 megawatts. (See Figure 5-4.)49
The United States, with more than 2,800 megawatts of capacity, is the world leader in tapping this energy source. But as a share of national electricity generation, other, smaller countries are far ahead. Whereas the United States gets only 1 percent of its electricity from geothermal energy, Nicaragua gets 28 percent and the Philippines, 26 percent.50
Most countries have barely begun to tap their wealth of geothermal energy. For countries rich in geothermal energy, such as those on the Pacific Rim, bordering the Mediterranean Sea, and along Africa's Great Rift, geothermal heat is potentially a huge source of energy—and one that does not disrupt the earth's climate. In Japan, an abundance of geothermal energy is close to the surface, as the thousands of hot spring spas throughout the country attest. It is estimated that the potential electrical generating capacity of geothermal energy in Japan could meet 30 percent of the country's needs. Some countries are so well endowed that they can run their economies entirely on geothermal energy.51
In a time of mounting concern about climate change, many governments are beginning to exploit the geothermal potential. The U.S. Department of Energy, for example, announced in 2000 that it was launching a program to develop the rich geothermal energy resources in the western United States. The goal is to have 10 percent of the electricity in the West coming from geothermal energy by 2020.52
47. International Geothermal Association, World Interactive Map Project, www.demon.co.uk/geosci/world.html.
48. From International Geothermal Association, www.demon.co.uk/geosci/igahome.html.
49. Figure 5-4 based on Seth Dunn, "Geothermal Power Rises," in Lester R. Brown et al., Vital Signs 1997 (New York: W.W. Norton & Company, 1997), pp. 50-51, with figure for 1998 from International Geothermal Association, www.demon.co.uk/geosci/wrtab.html.
51. Hal Kane, "Geothermal Power Gains," in Lester R. Brown et al., Vital Signs 1993 (New York: W.W. Norton & Company, 1993), p. 54.
52. DOE, "GeoPowering the West" Program, www.eren.doe.gov/geopoweringthewest/geopowering.html.
Copyright © 2001 Earth Policy Institute