Geothermal energy is a renewable energy source generated from hot, saline water occurring naturally in geothermal reservoirs. The temperature in the different layers of the subsoil increases with depth, because heat flows from the Earth’s core to the surface, thus heating the water in the subsoil.
In a geothermal plant, hot water is pumped through a well to the surface, where the heat is extracted by heat exchangers. The cool water is then pumped back into the ground. Large geothermal plants may consist of several wells for producing and injecting large volumes of water.
Geothermal energy is used for district heating
The hot water contains energy that can be exploited in some areas of Denmark, as long as the right geological layers are present and are of a sufficient thickness. Moreover, the layers must be porous and permeable, allowing water to flow through them easily.
The layers containing the hot water should preferably be located at a depth below approximately 700 metres in order to produce sufficient heat for district heating purposes. Geothermal wells typically have a depth of more than 1,000 metres.
The temperatures in the Danish subsoil are too low to use the geothermal energy to produce electricity.
There are three geothermal plants in operation in Denmark. They are based in Thisted, Sønderborg and Amager (Copenhagen). In addition, a number of licences have been granted to explore the opportunities for using geothermal energy in certain areas.
The use of geothermal energy requires a licence
A licence from the state is required for the exploration and production of geothermal energy. The DEA issues licences for geothermal plants, while the municipalities are responsible for geothermal heating.
Geothermal energy and geothermal heat is not the same thing
Geothermal heat is extracted from the upper geological layers, and the wells are frequently no more than a few hundred metres deep. In geothermal heating, a heat pump is used to circulate a liquid in a closed circuit.
The municipalities administer geothermal heating licences and grant licences to drill wells of a depth of less than 250 metres. If wells for geothermal plants are to go deeper than 250 metres, the DEA must be contacted in advance.