Geothermal energy is thermal energy created in the Earth’s crust through slow decomposition of radioactive elements, chemical reactions, crystalization and solidification of melted material or friction appearing in tectonic plates movements. Quantity of such energy is so huge that it can almost be considered inexhaustible.

Exploitation of geothermal energy implies exploitation of energy accumulated inside the Earth’s in the form of hot water and steam or within hot dry rocks. A significant factor in the process is a difference of temperatures on and beneath the Earth’s surface. The temperature gradient, i.e. the increase of temperature per depth kilometer, is highest along the surface. It decreases with increasing the distance from the Earth’s surface.

In order to exploit geothermal energy it is necessary to use natural flow of water or to create such conditions. Basic principle is to drain the water from the surface into deeper layers, where it warms up by taking the heat accumulated in the Earth. Having obtained such high temperature it reappears on the surface.

Deeper within the Earth crust there are huge quantites of hot dry rocks which contain significant energy. Surface water cannot penetrate into these rocks by itself. In order for this energy to be used, it is necessary to shatter hot dry rocks below the surface to create a sufficient surface for transfering rock heat onto the water. In such cases the surface water would reach broken rocks via an artificially created well, so-called injection well, and the heated water would be led onto the surface via a second well, so-called production well. Commercial profitability of exploiting hot dry rock energy and hot water in huge depths still hasn’t been technologically elaborated.

Geothermal energy is nowadays being used in many countries for the following purposes:

• therapy and recreation,
• heating and preparation of hot water,
• electricity production,
• agriculture (e.g. heating greenhouses, fishponds, land),
• industry.