Geothermal Renewable Energy
Geothermal power is energy derived from the heat of the earth's core. "Geo" means "from the earth" and "thermal" means "heat." This type of energy is clean and predictable, offering a reliable and renewable energy source.
Steam to Electricity
To understand how electricity is produced at The Geysers, it is helpful to know how geothermal energy begins. Molten rock, or magma, exists very deep in the earth where temperatures are extremely high. However, magma is relatively close to the surface in a few areas, particularly the volcanically active areas around the Pacific Rim. At The Geysers the magma is believed to exist at least four miles below the earth's surface. The heat from the magma radiates to the layers of rock above heating water in the pores and fractures of the hot rock. A small portion of the heated water may rise to the surface causing hot springs, geysers, and fumaroles. At The Geysers, the reservoir water boils to steam and is trapped by an overlying layer of tight, unfractured rock, called cap rock.
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Wells, some more than two miles deep, drill through the cap rock and tap the natural steam, which is piped to the 21 generating units at The Geysers complex. In the process steam is cleansed of tiny particles of rock that could damage turbine blades. Steam is then put to work spinning turbine generators in the power plants to create electricity.
Turbines are designed to operate with steam at 350 degrees Fahrenheit and 100 ponds of pressure per square inch. About two million pounds of steam per hour are necessary to operate a 110- megawatt-generating unit. After passing through the turbine, spent steam goes through a condenser where it is cooled and turns back into water. With existing technology, approximately 25 percent of the water is recycled back into the steam reservoir with the remainder lost to evaporation.
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