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Cross-section through the Alpine upland.
© Rödl&Partner
Copious thermal resources in the Munich geothermal region
24.04.2012

The geothermal plant in Unterhaching generates electricity and heat.
© Geothermie Unterhaching

Heat from deep underground can be used for a long time

The region between the Swabian and Franconian mountains and the Northern Alps has large thermal resources underground (geothermal energy). The availability of this hot water at depths of between 1,500 and 5,000 m has led increasingly more local communities in the region to rely on geothermal energy as a mainstay for their local energy supply. The extent to which these geothermal plants can be operated stably in the long term has been investigated by the Leibniz Institute for Applied Geophysics (LIAG) in Hanover, which has now published its findings. These results suggest that long-term use is viable.

Once the heat has been extracted, the water from the geothermal plants is injected back underground again. During the next 50 years, the water fed back is only expected to have a significant thermal impact on the overall temperature of the thermal water layers (aquifers) in areas immediately adjacent to the respective injection wells. The wells will not mutually impact each other in terms of the temperature. Mutual hydraulic impacts are also unlikely. These are significant findings, given that several neighbouring districts are planning to use the same thermal water aquifer in the Molasse Basin.

The calculation model

In 2009, seismic surveys were conducted on the subsurface below Unterhaching. This information along with further data and the subterranean models developed from them were used to conduct numeric forecast modelling. This calculation model can simulate various extraction scenarios and compare them to actual pump and extraction data. The calculation model was calibrated so that it can reproduce the hydraulic and geothermal conditions as well as the pump tests conducted in the region. The cooperation project, which was jointly conducted by LIAG together with partners from universities and business, was funded as part of the energy research conducted by the German Federal Ministry of the Environment.

Geothermal study and background

The region between the Swabian and Franconian mountains and the Northern Alps, also known as the South German Molasse Basin, has the most important reservoir for geothermal energy in central Europe. Ten geothermal plants with a total output of more than 11 MW are currently in operation there and a further eleven plants are now under construction. LIAG has set up a homepage for the “Geothermal characterisation of fissure karst aquifers in the Munich region” project, from which a study report can be downloaded.

A typical geothermal plant consists of two wells. Once hot water is extracted from the first well, the heat is recovered above ground and the water is then reinjected underground through the second well. The harnessed energy is then used for public heating supplies and for generating electricity.
A large reservoir for geothermal energy is located in the fissure karst aquifers in the Malm, another description for the Upper Jura. The layers of most interest for geothermal energy (upper or top Malm) lie at depths between 1,500 and 5,000 m, with temperatures ranging between 85 and over 140 °C. In the Southern Molasse, thermal water resources above 100 °C can be found at depths of approx. 3,000 m, which are suitable for geothermal electricity generation. The karstification recedes towards the south, meaning that geothermal test wells must be as close as possible to the geological fault zones in order to be successful. Breaks, fractures and fissures in these zones can provide high volumes of thermal water.

More from BINE Information Service

The Unterhaching geothermal research power plant is also located in the region. The plant is described in the BINE Projektinfo brochure “Geothermal electricity generation combined with a heating network”.

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