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Geothermal Power Plants





 




U.S. Department of Energy - Energy Efficiency and Renewable
Energy


Geothermal Technologies Program


Geothermal Power Plants



Geothermal power plant in the Imperial Valley,
California.


There are three geothermal power plant technologies being used to
convert hydrothermal fluids to electricity. The conversion
technologies are dry
steam, flash,
and binary
cycle. The type of conversion used depends on the state of the
fluid (whether steam or water) and its temperature. Dry steam power
plants systems were the first type of geothermal power generation
plants built. They use the steam from the geothermal reservoir as it
comes from wells, and route it directly through turbine/generator
units to produce electricity. Flash steam plants are the most common
type of geothermal power generation plants in operation today. They
use water at temperatures greater than 360°F (182°C) that is pumped
under high pressure to the generation equipment at the surface.
Binary cycle geothermal power generation plants differ from Dry
Steam and Flash Steam systems in that the water or steam from the
geothermal reservoir never comes in contact with the
turbine/generator units.


U.S.
Geothermal Power Plants


Power plant photographs








  

  • Utah

    • Dry Steam Power Plants


    Photo of dry steam power plants.

    Dry steam power plants at The Geysers in
    California.


    Steam plants use hydrothermal fluids that are primarily steam.
    The steam goes directly to a turbine, which drives a generator that
    produces electricity. The steam eliminates the need to burn fossil
    fuels to run the turbine. (Also eliminating the need to transport
    and store fuels!) This is the oldest type of geothermal power plant.
    It was first used at Lardarello in Italy in 1904, and is still very
    effective. Steam technology is used today at The Geysers in northern
    California, the world's largest single source of geothermal power.
    These plants emit only excess steam and very minor amounts of
    gases.






    alt="Illustration of a Dry Steam Power Plant - Geothermal steam comes up from the reservoir through a production well. The steam spins a turbine, which in turn spins a generator that creates electricity. Excess steam condenses to water, which is put back into the reservoir via an injection well."
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    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.

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    Illustration of a Flash Steam Power Plant - Pressurized geothermal hot water comes up from the reservoir through a production well. The water enters a flash tank where it depressurizes and flashes to steam. The steam then spins the turbine, which in turn spins a geneator that creates electricity. Excess steam condenses to water, which is put back into the reservoir via an injection well.


    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. Because this is a
    closed-loop system, virtually nothing is emitted to the atmosphere.
    Moderate-temperature water is by far the more common geothermal
    resource, and most geothermal power plants in the future will be
    binary-cycle plants.






    Illustration of a Binary Cycle Power Plant - Illustration of a binary-cycle power plant. Geothermal hot water comes up from the reservoir through a production well. The hot water passes by a heat exchanger that is connected to a tank containing a secondary hydrocarbon fluid. The hot water heats the fluid, which turns to vapor. The vapor spins a turbine, which in turn spins a generator that creates electricity. The hot water continues back into the reservoir via an injection well. This closed-loop system produces no emissions.


    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. We believe the result will be about 15,000 megawatts
    of new capacity within the next decade.


    DOE Support


    The U.S. Department of Energy recognizes the strategic value of
    geothermal electricity, and supports its development in several ways
    through its Geothermal Technology Development Program. First, it
    works with Congress to ensure support for geothermal energy and
    renewables in general. Second, it sponsors millions of dollars in
    research and development at national laboratories and universities.
    Investigators are working on issues in exploration, geochemistry,
    drilling, resource usage, and equipment operation. Third, through
    its GeoPowering the West initiative, it works with state and local
    officials and other stakeholders to identify and overcome regulatory
    and institutional barriers to geothermal power development.



    Utah Geothermal Area
    Nevada Geothermal Area
    Navy 1 Geothermal Area
    The Geysers Geothermal Area
    Imperial Valley Geothermal Area
    Honey Lake Geothermal Area
    Hawaii Geothermal Area
    Casa Diablo Geothermal Area