Ever since the earth was formed, huge amount of heat energy has been stored in its molten core. Some of this heat is always flowing towards the surface. This heat is called Geothermal Energy.
The hot interior of the earth heats up the layers of rocks above it. The water trapped in porous rocks near the surface of the earth also gets heated to high temperatures. The hot water may come out to the surface through the fissures in the rocks. Hot water springs and geysers are the best known examples of geothermal energy.
The diagram given below shows how the earth's heat can be used to produce hot water at the surface.
Geothermal Power Station
Heat from deep, hot dry rocks are used. A borehole is drilled deep into the granite. A small explosion is set off at the bottom of the hole causing the rocks to crack. A second borehole is then drilled into the cracked rocks. Water is pumped down the first hole and forced through the cracks. The water gets heated and returns through the other hole as hot water. This energy equals to that stored in 10,000 million tones of coal.
In some parts of the world, such as Iceland hot water comes naturally to the surface as steam which can drive turbines to generate electricity. Some power stations make use of lava that flows from the volcanoes.
