The development of more sustainable, cleaner and cheaper sources of energy is being driven by the depletion of fossil fuels and their impact on our environment through release of greenhouse gases. Geothermal energy is one of these upcoming new sources that today is relatively untapped but its potential can be seen in countries such as Iceland where 25% of its electricity and 90% of its heating is obtained from geothermal power. This energy is derived from the thermal energy beneath the earth's surface that resulted from the original formation of the earth as well as the radioactive decay of elements uranium, thorium and potassium. On average one kilometre of depth corresponds to a rise in temperature of about 20oC. The temperature inside the earth melts rock and also heats up water trapped in cracked and porous rock to create geothermal reservoirs of hot water and steam. Geothermal power plants rely on these reservoirs to harness the heat energy to produce electricity by drilling deep wells into the earth and piping steam or hot water to the surface and using it to drive generator turbines. This water is then piped back into the reservoir through injection wells to be reheated and thus with careful management to maintain the viability of these reservoirs makes this process of obtaining energy, sustainable. Geothermal power plants emit approximately 1% of the sulphur dioxide, <1% of the nitrous oxide and 5% of the carbon dioxide that is emitted by a similar sized coal-fired power plant. Geothermal energy has an advantage over other renewable energy resources such as solar or wind energy in that it can provide us with a consistent and more reliable supply of power. There was 8,933 MW of installed capacity in 24 countries with geothermal power plants in 2005 and this has risen by almost 20% to 10,715 MW which generates 67,246 GWh/year in 2010 according to a report by the International Geothermal Association.
The United states leads the world in the production of geothermal electricity with an installed capacity of 3,086 MW which is equivalent to the electricity obtained from burning 60 million barrels of oil.[1,4] This 3,086 MW relates to only less than 0.5% of the United states total electricity usage and shows how much of an untapped resource it is today. However there are a few problems that need to be overcome to promote the development of geothermal power plants. One of these problems is the high costs of drilling wells which can be between $2.3-4.0 million for a depth of 1500-3000 meters.[5 ]Another problem is the limited areas in which the conditions are suitable, which was normally an area near the boundaries of tectonic plates. Although this problem is currently being resolved with the development of Enhanced Geothermal Systems technology that allows us to create our own geothermal water reservoirs. With most governments know realizing the effects of green house gases on our environment, geothermal energy will definitely be considered as a potential sustainable energy resource and may even be considered better option in countries such as Ireland where the development of a nuclear power plant will most likely be met with a large opposition.