Geothermal energy is generated from the earth's heat that is found in high temperature water below the earth's surface. Geothermal energy for electricity was first produced at Lardarello , Italy in 1904 and is used in large quantities by many countries today. Wells are drilled through sedimentary or fractured rock, allowing hot steam or water to flow upwards to ground level.
Three types of power plants are used to generate geothermal energy, dry steam, flash, and binary. Steam power plants use the steam to power the turbine that drives the generator. Flash power plants take the hot water from the ground, allow it to boil, and then use the power to generate geothermal energy. The hot water in binary plants flows first through heat exchangers, bringing the water to a boil and thus providing the energy to spin a turbine. Any condensed steam or geothermal fluid that remains is injected back into the rock where it continues to generate heat.
The largest producer of geothermal energy in the United States is the Geysers in California which generate over 1,000 megawatts of power. Waste management is effectively used by recharging the Geysers with treated sewage that is piped into the geothermal area, replenishing the steam for generators.
With the rising prices of oil, gas, and coal, other states and countries are viewing geothermal energy as a cost-effective, renewable energy source . The earth's heat is so vast that it would take years, if ever, for this renewable energy source to disappear.