The nearer you get to the Earth’s centre the hotter it becomes. Nuclear reactions, caused by the decay of radioactive materials, constantly heat the molten core to 7200ºF (4000ºC). Because of this geothermal energy it is several degrees warmer at the bottom of a mine than it is at the top.
In some places hot rocks lie quite near the surface, causing hot springs, geysers or steam to rise out of the ground. These can be used to produce electricity.
The first geothermal power station was built in 1904, at Larderello in northern Italy, where steam was coming out of the ground at temperatures between 280ºF and 500ºF (140ºC and 260ºC). The steam was piped to turbines which powered generators.
In New Zealand, the Philippines, California and Mexico, power stations have been built where the Earth’s heat reaches the surface naturally. In some cases there may be o water present at all, just dry hot rocks, whose heat can only be used if water is pumped down to them and then recovered as steam. The steam is then used to drive turbines and generate electricity.
The granites of Cornwall are a source of geothermal energy that has recently been tested. Some 6500ft (1980m) beneath Camborne in Cornwall, the rocks reach temperatures of about 158ºF (70ºC).
To extract energy two boreholes would have to be drilled, cold water pumped down one and pressurized hot water returned up the other. The water would flow from one borehole to the other through fissures in the rock created by blasting it with explosives. Although the water is at 390ºF (200ºC), the pressure it is under prevents it from boiling. But when it is returned to normal atmospheric pressure at the surface, it instantly “flashes’ into steam – ready to drive the turbines.
Like other sites where geothermal energy could be tapped, Camborne has several problems. Minerals will have to be removed from the hot water, otherwise they could fur up pipes and corrode turbines. Tests have also shown that only one-third of the water pumped down finds its way back to the surface – the rest is lost. The third problem will be drilling deep enough.
If all these problems can be solved, the potential is enormous. It has been calculated that the Cornish granites alone contain as much energy as the whole of Britain’s coal reserves.
More and more countries are looking into geothermal energy as an alternative to fossil fuels. A major power station has been started in New Mexico, and a joint French and German project is being carried out near Strasbourg.
Picture Credit : Google