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Hydroelectric & Geothermal Power


Hydroelectric power takes advantage of the energy from falling water to turn turbines connected to electric generators. Although construction of dams is expensive, existing dam/hydropower complexes do not have fuel costs and hydroelectricity can be relatively inexpensive. Competing needs for recreation, wildlife habitat, and agricultural and urban water must be considered in determining the timing and amount of water releases at hydroelectric dams. In years with reduced rainfall, less water is available for release and hydropower generation may be reduced.

Major generators or marketers of hydroelectric power in the U.S. include:

  • Bonneville Power Administration (BPA). Founded in 1937, the BPA is a federal agency that markets electrical power in the Pacific Northwest, including hydroelectric power generated by 31 federal hydro projects in the Columbia River Basin. The dams are owned and operated by the U.S. Army Corps of Engineers (21 dams) and the Bureau of Reclamation (10 dams).
  • Bureau of Reclamation is a federal agency that was established in 1902 to manage water resources in the West. Now part of the U.S. Dept. of Interior, the Bureau operates 58 hydroelectric power plants, including Hoover Dam on the Colorado River and Grand Coulee on the Columbia River.
  • New York Power Authority is a state-owned organization that operates a number of hydroelectric facilities, the largest of which is the Niagara Power Project with a total of 25 turbines located several miles downstream of Niagara Falls.
  • Tennessee Valley Authority (TVA). The TVA was established in 1933 to generate power and control flooding on the Tennessee River. Today, TVA operates 29 hydroelectric dams and manages 47 reservoirs. Despite producing significant amounts of hydropower, however, TVA's power portfolio today is dominated by coal-fired (60%) and nuclear power (30%).
Hoover Dam Supplies Hydroelectric Power to Nevada, Arizona and California

Hoover Dam, on the Colorado River between Arizona and Nevada, was built between 1931-1935 to provide flood control and hydroelectric power.

Intake structures in Lake Mead behind the dam allow water to enter the penstocks, or pipes, that flow water to the turbines.

Rushing water flows through 17 turbines, each of which is connected to an electric generator.

After flowing through the turbines in the Hoover Powerplant, water is released back into the river below the dam.

The Federal Energy Regulatory Commission (FERC) issues licenses for new hydroelectric projects (and relicensing of existing projects), and also is responsible for ongoing oversight of dam safety and environmental monitoring.

Geothermal Power

Geothermal energy is heat energy from the earth's interior, brought near the surface by the movement of molten rock (magma). Geothermal resources take the form of heated water or steam, at or near the surface of the earth. Wells are drilled to tap the resource, and steam pressure is used to drive turbines that turn electric generators. Wells may produce steam that is used directly, or a mixture of steam and water which is separated before the steam is piped to the turbines. Binary geothermal plants use geothermal heat energy and a heat exchanger to boil a liquid with a boiling point lower than that of water, so that vapor is created at lower temperatures. Research also is underway to inject water into "hot dry rock" to produce steam. Geothermal plants require cooling towers, using either air or water cooling, to regulate temperatures in the turbines. Because geothermal heat energy is "always on," geothermal power is a source of baseload electricity.

U.S. Geothermal Resource Map (Source: U.S. Dept. of Energy)

California leads the U.S., and the world, in geothermal power production. Calpine Corp. operates 17 geothermal power plants in Northern California, making it the largest producer of geothermal electricity in North America. The 17 plants, collectively called The Geysers, utilize steam from over 350 active wells. The company, which also operates a number of natural gas-fired power plants, filed for Chapter 11 Reorganization in 2005 but emerged from bankruptcy at the beginning of 2008 with its commitment to geothermal power generation intact.

As part of its RE<C, Renewable Energy Cheaper Than Coal, Google announced plans to invest in geothermal power generation, as well as wind and solar.

Geothermal Power Plant at the Southern End of the Salton Sea, owned and operated by CalEnergy, sells clean power to Southern California Edison (note cows grazing happily in the foreground!).

Pros and Cons. In areas with geothermal resources, this source of power offers many benefits: no fuel is required, power can be generated continuously ( thus supporting baseload demand), and very few emissions are generated. Depending on the geology of an area, geothermal vapors may include hydrogen sulfide ("rotten egg gas"), which can be converted to elemental sulfur, and carbon dioxide. However, releases of CO2 from geothermal power generation are much lower than releases from burning of fossil fuels.

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Use of geothermal resources for direct heating of buildings, and for heat pump heating/cooling systems...


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