As with any renewable energy source, availability at reasonable cost is the main criteria. It is the same with geothermal energy. Since geothermal is tapping the underground thermal reservoirs, nearness to the earth’s surface is an important criteria. Not all places on earth are suitable for geothermal power plants.
The current geothermal capacity is around 10,000 MW. This is expected to more than double in the next few years.
Where are Geothermal Powerplants Currently Used?
The main countries that have large geothermal power plants are United States, Philippines, Mexico, Italy and Indonesia. Eighty Five % of the present geothermal generation are in countries that lie on the “Ring of Fire." Ring of Fire is the geographical locations on the Pacific Rim that have high volcanic and earthquake activities.
Significant generation outside of the “Ring" are in Italy and Iceland. Italy was the pioneer in the use of geothermal resources with the first geothermal plant starting in 1904. Iceland is one country that has the maximum percentage of public power generation and heating from geothermal.
Another potential area that is getting prominence is the “African Rift", the area along the East coast of Africa.
How are Potential Geothermal Areas Determined?
Underground rocks with a high thermal gradient, permeability of these rocks to allow the flow of fluids, and perpetual supply of fluids are the main requirements of a geothermal source.
Generally locations near to places with volcanic activity, places with geysers, hot water springs and the like are potential geothermal sites. Areas subject to tectonic plate movements and frequent earthquakes are also potential areas. However, it is not necessary that these have to lead to a viable thermal reservoir. There could be blind geothermal resources as well with no indications at the top surface.
Thermal imaging and electric and magnetic imaging are some of the methods applied in searching for geothermal energy sources. Shallow temperature prospecting is another method to make a preliminary find, as is finding the ratio of Helium isotopes in groundwater. More Helium 3 can indicate potential geothermal reservoirs.
Trial and error drills are the best way, but a costly proposition. The risk of the unknown is what makes the initial investments in geothermal much costlier than other forms of power generation. Developing in established areas to augment capacity is less risky. In most cases, it is accidental finds during oil prospecting that lead to the discovery of geothermal reserves.