Dependable energy from the earth’s depth
Energy extracted from geothermal heat – geothermy – is an environmentally-friendly, CO2-free, and inexhaustible energy source at a human scale, which is made available directly from the interior of the earth. It exists virtually everywhere, and is available at all times. Whether it is already visible in the form of a hot spring bubbling up directly on the earth’s surface, or in the form of heat deep down underground, geothermy will and is intended in future to join the other renewable energy sources to gradually replace heat and power supplies currently relying on fossil fuels (coal, oil, gas) and nuclear power.
Geothermy is generally divided up into two different types, each with their own extraction processes:
Shallow geothermy with boreholes down to approx. 400 m depth; and deep geothermy with boreholes extending to depths from 400 to around 6,000 metres below ground level.
Shallow geothermy harnesses low geothermal temperatures of up to approx. 25 °C, and mainly uses it for the heating of individual homes or commercial buildings. Heat pumps are required in this technology to boost the efficiency further.
Deep geothermy has access to higher temperatures so that this technology only requires the use of heat exchangers. The heat extracted in this way is primarily fed into district heating systems or used for power generation. Deep geothermy for power generation only makes economic and technical sense in most cases if the temperature of the geothermal source is over 100 °C.
Different technologies are used for this purpose:
- Deep geothermy well (GTW – geothermal well)
A single well is drilled down to a depth of approx. 3,000 m, and is then used to circulate liquid at a slow flow rate within a closed circuit. No liquids are exchanged underground. The heat absorbed underground by the circulating liquid is extracted at the surface to produce energy.
- Hydrothermal doublet (or triplet)
Hot formation water from a deep water-bearing rock horizon is brought to the surface in a production well. After extracting/using the thermal energy in this liquid by passing it through a heat exchanger, the cooled water is then pumped back down into the formation again via an injection well.
- Hot-Dry-Rock process (also known as EGS – Enhanced Geothermal System)
Fractures and fissures present in deeply buried rocks (and/or artificially created) are used to heat up water which is pumped down to the deep horizon via an injection well. As the water is heated up by the ambient high temperatures existing in the formation, it migrates through the fractures towards a production well drilled into the same formation some distance from the injection well, where the hot water is then pumped back up to the surface.
The geological conditions existing in Germany are favourable for the development of deep geothermal energy, particularly in Southern Bavaria, the Upper Rhine Graben, and also in North Germany – which has significant geothermal potential although this has been put to very little use in the past.
As part of its “National plan of action for renewable energy sources”, the German government is keen on seeing a significant expansion in the use of this technology – with the gradual aim of making the country independent of fossil fuels in the future by exploiting geothermy in addition to other renewables.