What is geothermal energy

A.� 'Geo' means earth, and 'thermal' means heat, so geothermal means 'earth heat'. Geothermal energy is produced by the heat of the earth and is normally found in volcanic and seismically active regions.

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Q.� What creates geothermal energy

A.� Rocks beneath the Earth's crust become progressively hotter the deeper you go: about 3 degrees celsius for every 100 metres. Water that comes into contact with such hot rocks becomes steam or very hot water, almost 150 degrees celsius. If this water or steam makes it through a crack in the Earth's surface it appears as a geyser or hot spring, either of which can be used to produce energy.

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Q.� How is geothermal power harnessed

A.� Wells are used to tap into underground sources of geothermal energy, bringing the steam or hot water to the surface in pipes. It is then distributed directly to heat buildings or fed into power plants to generate electricity.

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Geothermal power plants work pretty much the same as normal power plants: the energy source, in this case steam or hot water, is fed into a special turbine connected to a generator to make electricity. The cooled water can then be pumped back below ground to be reheated by the earth.

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The electricity is then fed through transmission wires to power homes, school and businesses.

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In practice the steam from high-temperature geothermal fluids is used to power turbines and generate electrical power, while lower temperature fluids provide hot water for directly heating buildings as well as hot or warm springs at spa resorts.

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Q.� How successful is geothermal energy

A.� Where it's available it can be very successful. For example, geothermal heat warms more than 70 percent of the homes in Iceland. The Geysers geothermal field near Santa Rosa, in Northern California, USA produces enough electricity to meet the power demands of San Francisco.

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Q.� How 'green' is geothermal energy

A.� Geothermal energy occurs naturally, although it isn't strictly renewable. It avoids many of the pollution problems associated with fossil fuels and nuclear energy. Land use for geothermal wells, pipelines, and power plants is small compared to land use for other extractive energy sources, such as oil, gas, coal, and nuclear.

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Chemical and mineral concentrations within the steam and water, such as sulphur, gold and mercury, can be extracted and used elsewhere. In fact the natural fluids do contain some potentially hazardous elements in a higher concentration, as a result of processing, which need to be extracted before the water is pumped back into the ground.

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Do you want to know how an alternative energy system works Click here to read about wind farms or here to post a question about another energy source.

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by Lisa Cardy