1 GEOTHERMAL ENERGY

2 Geothermal power is generated by mining the earth's heat. In areas with high temperature ground water at shallow depths, wells are drilled into natural fractures in basement rock or into permeable sedimentary rocks. Hot water or steam flows up through the wells either by pumping or through boiling (flashing) flow. Experiments are in progress to determine if a fourth method, deep wells into "hot dry rocks", can be economically used to heat water pumped down from the surface. A hot dry rock project in the United Kingdom was abandoned after it was pronounced economically unviable in HDR programs are currently being developed in Australia, France, Switzerland and Germany. Magma (molten rock) resources offer extremely high-temperature geothermal opportunities, but existing technology does not allow recovery of heat from these resources.hot dry rocksUnited KingdomAustralia FranceSwitzerlandGermanyMagma

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4 People who live in these areas are receiving electricity from geothermal power plants

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6 This historical drawing depicts Native Americans using hot springs at what is now Calistoga, California. Some tribes considered hot springs to be neutral territory where no wars were allowed. This small greenhouse is heated with geothermal water. Plants grow faster and larger when they have additional heat available

7 Geothermal water is also used for industrial uses, like drying lumber or food products. This plant in Brady, Nevada, provides dried onions to Burger King Pipes of geothermal water can be installed under sidewalks and roads to keep them from icing over in winter, like this sidewalk in Klamath Falls, Oregon

8 There are three geothermal power plant technologies being used to convert hydrothermal fluids to electricity. The conversion technologies are dry steam,dry steam Flash binary cycle The type of conversion used depends on the state of the fluid (whether steam or water) and its temperature.

9 Dry Steam Power Plants Steam plants use hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity It was first used at Lardarello in Italy in 1904, and is still very effective

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11 The first modern geothermal power plants were also built in Lardello, Italy. They were destroyed in World War II and rebuilt. Today after 90 years, the Lardello field is still producing. The first geothermal power plants in the U.S. were built in 1962 at The Geysers dry steam field, in northern California. It is still the largest producing geothermal field in the world.

12 Flash Steam Power Plants Hydrothermal fluids above 360°F (182°C) can be used in flash plants to make electricity. Fluid is sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or "flash." The vapor then drives a turbine, which drives a generator. If any liquid remains in the tank, it can be flashed again in a second tank to extract even more energy.

13 Flash technology was invented in New Zealand. Flash steam plants are the most common, since most reservoirs are hot water reservoirs. This flash steam plant is in East Mesa, California.

14 This flash plant is in Japan. In flash plants, both the unused geothermal water and condensed steam are injected back into the periphery of the reservoir to sustain the life of the reservoir.

15 Binary-Cycle Power Plants Most geothermal areas contain moderate-temperature water (below 400°F). Energy is extracted from these fluids in binary-cycle power plants. Hot geothermal fluid and a secondary (hence, "binary") fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the turbines

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17 Binary technology allows the use of lower temperature reservoirs, thus increasing the number of reservoirs that can be used. This binary plant is at Soda Lake, Nevada

18 This binary power plant, at Wendell- Amadee, California, runs by itself. If it detects a problem, it automatically radios the operator to come to the site

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23 These geothermal plants are operating successfully in a Philippine cornfield, at Mammoth Lakes, Calif., in the Mojave Desert of California, and in a tropical forest, at Mt. Apo, Philippines.

24 Turbine generator outdoors at an Imperial Valley geothermal power plant in California

25 Turbine generator in a geothermal power plant in Cerro Prieto, Mexico

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29 The Future of Geothermal Electricity Steam and hot water reservoirs are just a small part of the geothermal resource. The Earth's magma and hot dry rock will provide cheap, clean, and almost unlimited energy as soon as we develop the technology to use them. In the meantime, because they're so abundant, moderate-temperature sites running binary-cycle power plants will be the most common electricity producers. Before geothermal electricity can be considered a key element of the U.S. energy infrastructure, it must become cost-competitive with traditional forms of energy. The U.S. Department of Energy is working with the geothermal industry to achieve $0.03 to $0.05 per kilowatt-hour.