Guide Note

Geothermal Power is created from energy which is stored beneath the earth's surface. Unlike solar or wind power, geothermal energy is unaffected by weather conditions, so it provides a stable source of power all day, every day. The price of geothermal energy is relatively stable in contrast to fossil fuels which are subject to extreme fluctuations in price.

Fast Facts

1. Named for the Greek words for earth (geo) and heat (therme)
2. First geothermal generator: 1904 in Larderello, Italy
3. Largest group of geothermal power plants: The Geysers, California

Traditional geothermal power is generated using steam that is present below the earth. The steam is pumped to the surface and used to power a generator. The latest technology, known as Enhanced Geothermal Systems, or EGS, pumps water down into hard rock to generate steam that can be used for power.

The hot water used in the geothermal process can be re-injected into the ground to produce more steam.

Geothermal steam has been used for centuries for bathing and heating. Electricity was first generated from geothermal power in 1904, when Prince Piero Ginori Conti used energy from the dry steam fields in Larderello, Italy, to power four light bulbs. A geothermal power plant was built on those fields in 1911, and remained the only industrial plant in the world until 1958, when one was built in New Zealand. The Geysers Resort Hotel in California, however, built a private plant to accommodate the hotel's electricity needs in 1921. The plant wasn't price competitive with the cheap coal that was available at the time, so the hotel discontinued using it. In 1960, Pacific Gas and Electric opened the first commercial United States geothermal power plant at The Geysers.

Geothermal power is used commercially in 70 countries around the world, but currently accounts for less than 1% of the world's energy. Massachusetts Institute of Technology scientists estimate that there is enough geothermal energy in the hard rocks located 10km below the United States to provide all the world's energy for 30,000 years.

The principal environmental concern of geothermal power plants relates to the risk of land instability that may be caused by injecting water deep into areas of dry rock which do not naturally contain water.

Geothermal power is scalable, in that the size of the plant can be tailored to the energy needs of the region. A large power plant could be erected to supply power for a city, while smaller plants can service rural villages.