| Geothermal energy:
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| | reservoirs appropriate for direct-use
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| Geothermal power uses the natural sources
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| | systems are widespread throughout the
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| of heat inside the Earth to produce heat
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| | western United States. Geothermal power
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| or electricity. Currently, most
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| | plants convert hydrothermal fluids (hot
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| geothermal power is generated using steam
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| | water or steam) to electricity. The
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| or hot water from underground. Geothermal
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| | oldest type of geothermal power plant
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| power generation produces few emissions
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| | uses steam, accessed through deep wells,
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| and the power source is continuously
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| | to directly drive a turbine to produce
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| available.
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| | electricity. Flash steam plants are the
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| There are three geothermal technologies
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| | most common type of geothermal power
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| currently in use in the United States:
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| | plants in operation today. They use
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| direct-use systems, use of deep
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| | extremely hot water (above 300 degrees F
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| reservoirs to generate electricity, and
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| | (149 degrees C)), which is pumped under
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| geothermal heat pumps.
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| | high pressure to the generation equipment
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| In direct-use geothermal systems, a well
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| | at the surface.
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| is drilled into a geothermal reservoir to
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| | Estimated subterranean temperatures at a
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| provide a steady stream of hot water. The
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| | depth of 6 kilometers. The hot water is
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| water is brought up through the well, and
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| | vaporized and the vapor in turn drives
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| a mechanical system-piping, a heat
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| | turbines to generate electricity.
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| exchanger, and controls-delivers the heat
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| | Binary-cycle geothermal power plants use
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| directly for its intended use. A disposal
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| | moderate-temperature water (100-300
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| system then either injects the cooled
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| | degrees F (38-149 degrees C)). The water
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| water underground or disposes of it in a
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| | is used to vaporize a second fluid that
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| surface storage pond. Geothermal hot
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| | has a much lower boiling point than
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| water is used for heating buildings,
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| | water. The vapor from this second fluid
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| raising plants in greenhouses, drying
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| | is then used to drive the turbines to
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| crops, heating water for fish farms, or
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| | produce electricity. California, Hawaii,
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| for industrial processes, at hundreds of
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| | Nevada, and Utah currently have operating
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| sites around the country. Geothermal
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| | geothermal power plants.
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