Rocks deep below ground-level store heat, and stay at a fairly constant temperature. This heat is called 'geothermal energy'. Water that has flooded disused mines is warmed by the heat of the rocks. The idea of using geothermal energy is not new - the Romans used hot springs for heating.
Heat pumps are already used in many buildings around the world. Basically, the heat pump is the reverse of a domestic refrigerator.
In a refrigerator heat is pumped from the inside (where the food is stored) and released at the back. In so-called 'ground source' heat pumps, pipes are laid in the ground below or close to a building, and are then able to collect much more heat than is contained inside a refrigerator. Enough heat can be pumped from the ground to heat the building.
Heat pumps like this can also pump heat from a body of water such as a lake, a river... or a flooded mine. The mine water has the additional advantage of being warmer to start with.
Heat pumps typically generate three times as much energy as you put in - using the warm minewater increases this still further.
Mine water has already been used on a small scale for heating, but this has generally involved single buildings and a fairly small heat pump. In the proposed pilot projects the scale is larger, using a large heat pump. Instead of heating just one building, the system will supply heat for a district heating system. In this way the heat is supplied to a large number of buildings.
ZDROJ: www.ekobydleni.eu,Minewater project