Geothermal Energy

Geothermal power is energy generated by heat stored beneath the Earth's surface. As of 2007, geothermal power supplies less than 10% of the world's energy. Geothermal comes from the Greek words geo, meaning earth, and therme, meaning heat. Prince Piero Ginori Conti tested the first geothermal power plant on 4 July 1904, at the Larderello dry steam field in Italy. The largest group of geothermal power plants in the world is located in The Geysers, a geothermal field in California.

Electricity Generation

Three different types of power plants - dry steam, flash, and binary - are used to generate electricity from geothermal energy, depending on temperature, depth, and quality of the water and steam in the area. In all cases the condensed steam and remaining geothermal fluid is injected back into the ground to pick up more heat. In some locations, the natural supply of water producing steam from the hot underground magma deposits has been exhausted and processed waste water is injected to replenish the supply. Most geothermal fields have more fluid recharge than heat, so re-injection can cool the resource, unless it is carefully managed.

Flash Steam

Flash steam power plants use hot water above 182°C (360°F) from geothermal reservoirs. The high pressure underground keeps the water in the liquid state, although it is well above the boiling point of water at sea level. As the water is pumped from the reservoir to the power plant, the drop in pressure causes the water to convert, or "flash", into steam to power the turbine. Any water not flashed into steam is injected back into the reservoir for reuse. Flash steam plants, like dry steam plants, emit small amounts of gases and steam.