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Geothermal energy requires no combustion; its energy already exists as heat.1
Capital costs for geothermal installations are lower than for comparable-size fossil- or nuclear-fueled plants, and once a plant is built, there are no fuel costs.2
Where resources are abundant and accessible, geothermal power is already an energy bargain, usually less expensive than electricity generated by coal and nuclear plants.3
Geothermal energy is flexible in its applications. It is well-suited for integrated industrial use -- producing electricity, process steam, and heat for a a variety of industries and agricultural activities in a single region.4
There are no major economies of scale in production; small generating modules can be added one at a time as local development and need dictate.5
Geothermal characteristics change with the area, so exploration is not easy.6
Geothermal turbine efficiency is comparatively low due to the low temperature and pressure of steam input. Overall plant efficiency is estimated to be about 15 percent less than that of a fossil-fueled plant.7
There is uncertainty about how long each geothermal well will last.8
Possible environmental dangers posed by geothermal energy are:
The use of geothermal heat must occur near the source; it isn't possible to transport it very far.10
The geothermal energy supply is of low quality -- diffuse like solar rather than concentrated like coal.11
Geothermal energy is available where hot magma from the earth's core is located close to the surface and has heated deep reservoirs of water.12 A geothermal plant uses a steam collection system, turbine, generator, and pollution control equipment, with generating costs reported to be as low as $.05 per kilowatt-hour.13 Currently, the average geothermal unit is on-line more than 95 percent of the time.14
At present, geothermal power can be tapped only where molten rock lies close to the earth's surface, although technological advances may make it feasible to use deeper geothermal reservoirs and lower temperature geothermal water.15
The process used to tap dry steam geothermal energy (which is the source of more than 1100 MW of electricity generate at The Geysers geothermal plant 90 miles north of San Francisco) results in the release of hydrogen sulfide, ammonia, and radon. The process can be noisy, unless adequately muffled, and dissolved minerals in the team cause corrosion in the pipes, valves, and turbine. Research is underway to combat these problems.16
The overall potential of geothermal energy is limited by the relatively small number of high quality reserves of subsurface steam and hot water.17 Two thousand MW of installed geothermal capacity is already in place in the United States, and based on announced industry plans, U.S. geothermal capacity is expected to reach 4,700 MWe by 1995.18
1 Gabel, op. cit., p. 114.
3 Deudney and Flavin, op. cit., p. 219.
4 Gabel, op. cit., p. 115.
12 Robert C. Cowen, "Search for Alternatives to Nuclear Finds Promise Under the Sun," Christian Science Monitor, April 29, 1987, p. 14.
13 Flavin, Electricity's Future: The Shift to Efficiency and Small-Scale Power, op. cit., p. 36.
14 Energy Security, op. cit., p. 203.
15 Richard Munson, "Electricity: New Consumer Choices," Center for Renewable Resources, May 1985, p. 15.
16 Edison Electric Institute, "Alternative Energy Sources and Technologies," op. cit., pp. 31-33.
17 Flavin, Electricity's Future: The Shift to Efficiency and Small-Scale Power, op. cit., p. 36.
18 Energy Security, op. cit., p. 203.