Heat generation from groundwater: How much potential does geothermal energy have?

Status: 05/14/2022 10:45 a.m

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Since the outbreak of the Ukraine war, interest in import-independent energies has been growing. One method is geothermal energy, the generation of heat from groundwater. What potential does it hold?

The turning point in the energy sector has already arrived at the Munich combined heat and power plant. In addition to two classic gas and steam turbine systems, a new geothermal system has been in operation here for several months – according to the operator, one of the most modern in Europe. Water at a temperature of over 100 degrees is pumped out of the earth from a depth of around 3000 meters.

The plant produces enough energy to heat 80,000 Munich residents. The water is then fed back into the earth unchanged in a closed circuit. By 2040, the city wants to convert its entire heat supply to renewable energies – and is fully committed to geothermal energy.

Possibilities currently hardly used

The potential of thermal water from the depths is enormous: it is estimated that more than 25 percent of Germany’s heat requirements could be covered by hydrothermal geothermal energy alone, i.e. skimming off water reservoirs at a depth of up to four kilometers. Just as much energy is in the higher-lying hot water sources down to a depth of around 400 meters – this is referred to as so-called near-surface geothermal energy. Currently, however, only 1.5 percent of the total heat requirement in Germany is covered by geothermal energy.

Not every area is equally suitable for extracting geothermal heat from great depths. The prerequisites are rocks in the ground that can conduct groundwater, the so-called aquifers. The southern German foothills of the Alps, the North German Basin and the Upper Rhine Graben offer particularly favorable conditions. The better the geological conditions, the lower the probability that the well, which costs up to ten million euros, will not produce enough water.

Not without seismological risk

Hydrothermal geothermal power plants require careful planning and implementation, as well as comprehensive permitting procedures, to avoid damage from accidental ground uplift or subsidence. Even if drilling is carried out correctly, slight earthquakes can occur due to the pressure and temperature changes in the subsoil. However, these tremors usually remain far below the threshold of human perception. It is disputed whether geothermal systems in Germany can also trigger stronger earthquakes.

In the Bavarian municipality of Poing near Munich, however, several noticeable earthquakes up to a magnitude of 2.4 on the Richter scale were registered in 2016 and 2017, for which a recently built geothermal plant was held responsible. The operators found that existing stresses in the rock reacted sensitively to the introduction of cold water. As a consequence, the procedure was revised and a seismological monitoring network was set up that also accurately records smaller earthquakes. There have been no further incidents of this kind since then.