Geothermal energy is one of the oldest sources of energy. It is simply using and reusing (reusable energy) heat from the inside of the earth. Most of the geothermal energy comes from magma, molten or partially molten rock. Which is why most geothermal resources come from regions where there are active volcanoes. Hot springs, geysers, pools of boiling mud, and fumaroles are the most easily exploited sources. The ancient Romans used hot springs to heat baths and homes, and similar uses are still found in Iceland, Turkey, and Japan. The true source of geothermal energy is believed to come from radioactive decay occurring deep within the earth.
Electricity is one of the biggest outputs of geothermal energy. It was first recorded to produce electricity in 1904 in Italy. There are now geothermal power plants in operation in New Zealand, Japan, Iceland, the US and elsewhere.
For the generation of electricity, hot water, at temperatures ranging from about 700 degrees F, is brought from the underground reservoir to the surface through production wells, and is flashed to steam in special vessels by release of pressure. The steam is separated from the liquid and fed to a turbine engine, which turns a generator. In turn, the generator produces electricity. Spent geothermal fluid is injected back into peripheral parts of the reservoir to help maintain reservoir pressure. If the reservoir is to be used for direct-heat application, the geothermal water is usually fed to a heat exchanger before being injected back into the earth. Heated domestic water from the output side of the heat exchanger is used for home heating, greenhouse heating, vegetable drying and a wide variety of other uses. Hot water and steam exist at many subsurface locations in the western U.S.
These resources can be classified as low temperature (less than 194 degrees F), moderate temperature (194 302 degrees F), and also high temperature (greater than 302 degrees...