The interior of the earth is hot. It becomes hotter everywhere on earth with increasing depth. Coalminers experience this on a daily basis. The aim of geothermal systems is to utilise this naturally occurring energy to provide heat and energy.
Geothermal energy can be extracted from different depths. Heat near the surface to a depth of several hundred metres can be removed using ground-source heat pumps and shallow borehole heat exchangers. The hot water deposits that occur in rock strata at greater depths are extracted using hydrothermal geothermal technology. In order to extract heat from dry, crystalline rock, the hot-dry-rock process was developed (see graphic). In volcanically active regions, steam deposits and hot rock can be used for generating heat. This is particularly attractive from an economic view because the heat at this low depth has a relatively high temperature and drilling costs are mostly low. Geothermal energy is always available irrespective of the time of year or day and can therefore be used for basic supplies. But not all areas are suitable for expensive drilling operations, which are sometimes unsuccessful and in exceptional cases can even trigger earthquakes and tremors.
