Across the world, geothermal energy is mainly used for heating swimming pools, buildings, greenhouses and for urban heating systems. Water up to 200 degrees C is pumped from boreholes up to 5,000 meters deep. The heat is then extracted and the cooled water is pumped back in through a second bore.

This method of heat capture is feasible worldwide, inexpensive and increasingly popular in countries that lack volcanic activity. According to assessments by the Renewables Global Status Report, the installed capacity of geothermal heat plants is around 38 gigawatts worldwide -- more than double the capacity of geothermal power plants that generate electricity.

To date, China (14 GW), Turkey (3 GW), Iceland (2 GW) and Japan (2 GW) are the leaders in developing deep geothermal energy, heating more and more city districts and greenhouses. In Germany, the city of Munich enjoys inexpensive geothermal heating and has set its sight on using the technology to make the sector climate neutral by 2035.

The German government is also looking at further developing deep geothermal energy to create a nationwide climate-neutral heat supply by 2045.  According to studies, deep geothermal energy could generate around 300 terawatt hours of heat annually from an installed capacity of 70 GW -- more than half the future heat demand of all buildings.