How geothermal energy should change the heat supply

Geothermal energy How geothermal energy should change the heat supply As of: October 25, 2026 • 5:10 a.m

In Potsdam, more than a kilometer is currently being drilled into the ground in order to supply thousands of households with geothermal energy in the future. The technology harbors risks, but also many opportunities.

A 30 meter high drilling tower rises on the site of the Potsdam Süd thermal power plant. Drilling has been going on here since July, almost around the clock. The drilling is expected to go up to 1,500 meters deep.

The goal: to find as much warm water as possible in order to supply thousands of households in the Brandenburg state capital in the future. Potsdam wants to generate its district heating completely without fossil fuels by 2035. So-called deep geothermal energy is expected to play a central role in this.

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Around 78 million euros are planned for the project at the southern thermal power station. Those responsible are confident that the effort will pay off. But no one can predict exactly how much warm water can actually be extracted from the underground there. “You never know whether you’ll find what you’re looking for,” says Tristan Grüttner, project manager at the municipal energy supplier EWP. “But of course we did a lot of studies in advance.” And the first results show that we are on the right track, reports the project manager.

Further findings should be available by the end of the year. A decision will then be made as to whether additional drilling makes sense. They have already been successful at another location in Potsdam. The first geothermal system has been in operation since 2024 on the site of a former tram depot. It is already supplying an entire new building district with geothermal energy. With four megawatts of thermal output, the system delivers twice as much heat as originally expected.

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The principle is comparatively simple: the deeper you drill into the earth, the warmer it gets. In Germany the temperature rises on average by around three degrees per 100 meters. The warm water is pumped to the surface from deep layers of rock. There heat is extracted from it, which can be used for heating. The cooled water is then drained back underground.

Brandenburg in particular offers good conditions for this. The state lies largely in the North German Basin, where there are sandstone layers at great depths that store the warm water. “The central part of Brandenburg is in the best areas in terms of underground properties for geothermal energy,” says Ingo Sass from the Helmholtz Center for Georesearch in Potsdam. However, what is always crucial when drilling is that there must be enough water that can be pumped.

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Potsdam is not alone with its drilling. Geothermal energy is already being used or expanded in other Brandenburg cities such as Neuruppin and Prenzlau. Interest has grown significantly, especially since the energy crisis of 2022.

“We have five times as many projects in deep geothermal energy,” says Gregor Dilger, managing director of the Federal Geothermal Association. Many municipal utilities woke up to the war against Ukraine and the subsequent gas price crisis and realized: "We have to do something here."

Unlike wind or solar energy, geothermal energy is available around the clock. Nevertheless, it has so far only played a small role in heat supply. According to Economics Minister Martina Klement, only around 13 percent of the heat in Brandenburg currently comes from renewable energies. “We have room for improvement. But of course that also offers opportunities,” says the CSU politician.

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A major obstacle is the initially high exploration and development costs. The drilling alone costs millions of euros. If enough warm water is not found, there is a risk of high losses. This so-called discovery risk is difficult to bear, especially for smaller municipalities. In order to lower the financial hurdles, the federal government is now also stepping in with its own programs. For example, with cheap loans or a funding program for heating networks. Potsdam also receives funding from the federal government for its heat transition.

In the long term, however, according to Ingo Sass from the GFZ, deep geothermal energy would pay off as a stable, comparatively inexpensive and crisis-proof energy source. “It’s a question of investment distribution,” said Sass. However, there remain possible risks for people and the environment. Interference with the subsoil can trigger smaller earthquakes. Groundwater could also be endangered during drilling. However, experts believe these risks can be reduced through careful planning, modern safety technology and monitoring of the systems.

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A few kilometers further in the capital, the heat from the underground will also be used more extensively in the future. It was only on Monday that Berlin granted exploration rights for deep geothermal energy for the first time. Berliner Energie undwärme GmbH (BEW) is planning to drill a borehole to a depth of almost 2,000 meters at the Marzahn power plant site.

Four water-bearing rock layers are to be examined there. The results are intended to show whether geothermal energy can be used for the Berlin district heating network in the future. According to current plans, the first system could go into operation in 2031.

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Whether Potsdam, Berlin or other cities in Germany: more and more municipalities are relying on geothermal energy. But the expansion should move even faster.

This week, more than 550 experts from science, business and politics discussed how this can be achieved at the German Geothermal Energy Congress in Potsdam. The main topics included new technologies, financing and the political framework.

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This topic in the program: rbb | rbb24 Brandenburg current | Oct 19, 2026 | 7:30 p.m