Geothermal energy in Germany – the completely underestimated energy source

AndIt is a moment that Thomas-Tim Sävecke has been waiting for for many years, ten years to be exact. That moment when it will be clear whether all the sleepless nights, the nearly 23 million euros in funding, the nearly 20,000 flyers and public events were worth it. A moment that will show whether the long-awaited hot water reservoir will indeed be more than three kilometers below Hamburg – and Germany one step closer to its energy transition.

Source: WELT Infographic / Paul Daniel

Thomas-Tim Sävecke is head of geothermal energy at Hamburger Energiewerke, the municipal company of the Hanseatic city. For three months, the drill beneath Wilhelmsburg, a neighborhood south of the city, screwed towards its target at a depth of 3,000 meters. With each hour it rose up to 15 meters into the interior of the earth.

The first rock samples are currently being analyzed and in a few days will provide insights: Does the long-awaited layer of sandstone actually lie down there, up to one hundred meters thick and porous enough for the hundred-degree hot water to circulate there? If things go well, it could provide warmth from the depths to 5,000 families for up to 50 years.

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transformation of the century

This saved 7,000 tons of carbon dioxide. Sävecke, who has already installed solar and wind power plants all over the world and is very used to it, says today: “Then we managed to do it.” He also means the rock. Above all, however, the difficulties that he and his team have had to face up to now.

Geothermal energy is considered by many experts to be the most underrated source of energy, particularly geothermal energy that is more than 400 meters deep underground. Keeping homes warm accounts for more than half of the total energy required in Germany. A joint report by the Fraunhofer Society and the Helmholtz Association just determined that energy from the depths could provide more than a quarter of the heat in Germany. So far it’s less than one percent. Rolf Bracke, one of the authors of the report and head of the Fraunhofer Institute for Energy Infrastructure and Geothermal Energy (IEG), speaks of “homeopathic quantities”.

So far, a quarter of all apartments have been heated with oil, half with gas, half of which have so far come from Russia. 14 per cent of heat from district heating, which often still comes from coal-fired power plants. They still release far more carbon dioxide than allowed by the climate protection law. So, if the republic is to be climate neutral by 2045, a lot has yet to happen, including for homes.

Rolf Bracke says: “For a long time, the only talk about the energy transition was electricity.” Now we must finally look at the thermal transition. Above all geothermal. Not only is it more space-saving than wind and sun energy. But also independent of the time of day and the season.

In Hamburg this turnaround was addressed some time ago, in Munich it has been going on for 18 years. The metropolis now has six plants and the largest geothermal plant in Europe is currently under construction right in the center. In Bochum, Lübeck and many other places now want to follow suit. Suddenly it seems like something is happening with deep heat. But why only now? Why has it failed so far?

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At “risk of discovery”, says Inga Moeck, professor of applied geothermal and geohydraulics at the University of Göttingen, is responsible for the Hamburg project from a scientific point of view. By that you mean the uncertainty of whether something can be found down there in the depths.

It also speaks of the “most exciting moment of recent years” ahead of what is happening in Hamburg, so far such perforations have been so rare. Even with the success of the preliminary investigations, it is unclear whether the well itself will hit the much-desired water vein. Up to 70% of investments are considered uncertain in the first exploration phase. However, drilling alone costs up to € 15 million. A risk that many cities and communities do not want and cannot bear.

Geothermal plants in Hamburg

Geothermal power plant in Hamburg

Source: Hamburger Energiewerke

Looking back, Hamburg and Munich were lucky. Cities knew from previous gas and coal explorations that they were each on one of Germany’s most promising geothermal systems – hot water reservoirs between rock strata that can be used to generate power – the North German basin beneath the city. Hanseatic and the Molasse Basin of southern Germany under the Isar-Metropolis.

In addition, there was an ambitious city administration that carried out the approval and conversion process of the network and sought funding. And finally, especially in the case of Munich, a prosperity with which one could and wanted to afford expensive technology right from the start.

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It is often not known whether other regions of Germany are also sitting on such a treasure. The “white spots on the underground map” prevailed in many places, says Moeck. There is also “huge potential” in the land in many other areas. This includes much of northern Germany, the Rhine-Ruhr region and the Upper Rhine Graben.

Ultimately, according to Moeck, underground heat can be used nationwide, albeit at different depths and therefore at different temperatures. “From a not great depth, you can at least use it for heating.” Moeck then resumed the cause of filling many of the underground “white spots” with paint.

Water slows down the sound waves

And it works like this: to find out if there really is more to one spot, a so-called vibrating vehicle approaches, a giant truck with a futuristic appearance. With a metal stamp between the wheels, it generates vibrations underground. The sound waves released migrate into the depths, where limestone, clay, sandstone reflect them in a different way. Highly sensitive ground microphones capture reflections again. From lab tests, Moeck and his team know exactly how fast the waves travel through which material. The wave travels slower through water than through dense rock.

On site, they can then use the measured speeds to calculate where the material is stored and how deep the desired tank is. If it is too deep, the drilling becomes too expensive and complicated. If it’s just below the surface, it won’t bring enough heat. Shallow geothermal energy with a maximum depth of 400 meters provides correspondingly little energy and the water is therefore usually a maximum of 25 degrees.

Every hundred meters more, the closer you get to the lower crust of the earth, the temperature increases by an average of three degrees. Because there, at a depth of up to 40 kilometers, uranium, thorium and other radioactive elements decay. They release heat that flows outward from inside the earth. At a depth of 3,000 meters there are between 90 and 100 degrees, ideal conditions for providing warmth to families, just as Hamburgers currently hope.

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If Germany wants to increase the potential of geothermal energy, the republic would have to drill several thousand such wells, says Rolf Bracke of the Fraunhofer IEG. According to Bracke, the fact that it has not existed so far is also due to the old structures of the energy suppliers. Many municipal services had long been oriented towards low-cost coal, so it was difficult to change course and rebuild the heating network. He therefore asks for some sort of risk insurance for the communities.

Following the example of development cooperation, the federal government could set up a fund that funds exploration and initial drilling for municipalities. If you find something, the municipality has to pay back the money.

Geographical location, economic risk, old network structures: there is another reason why geothermal energy has not yet made its way: its image. Single incidents in the past had fueled fears of possible earthquakes or drilling damage. The Staufen im Breisgau case is particularly impressive. A full 15 years ago, presumably due to technical errors in a relatively shallow well, water seeped into a mineral layer, which swelled into gypsum and raised the city center in places. In another case, 17 years ago, drilling in Basel had generated a 3.4 magnitude earthquake and some buildings had cracked.

Avoidable and unnecessary damage to image

Marco Bohnhoff, professor at the Geoforschungszentrum in Potsdam, defines it as “absolutely avoidable” and “unnecessary damage to image”. He advocates a principle that must be even more taken into consideration: “Stimulate on sight”. The professor of experimental seismology and drilling proved that it works at a depth of six kilometers in the center of Helsinki.

In the Finnish capital, the authorities had established that no tremors of magnitude greater than two should be triggered and therefore would not be felt. “We had a maximum of 1.9,” Bohnhoff says with some pride in his voice. “And they were wanted.”

Low magnitude earthquakes

Because in order to exploit the heat of the depths, it is often first necessary to convert the subsoil into a kind of instantaneous water heater. In a well, hot water rises and releases its energy. Cooled in a second hole, it returns to the depth where it heats up again. A closed loop is created. To connect the two wells together, large quantities of water are pressed through the rock under high pressure. Cracks appear through which water can then circulate. Normally, there are only small vibrations that are not noticeable on the surface and usually cannot even be measured.

“We developed such a fine measurement network that we could hear even the smallest crackle in real time,” says Bohnhoff. A whole series of seismometers, that is high-sensitivity microphones, report every smallest micro-earthquake coming from wells several hundred meters deep. In addition, a software that calculates the origin of the earthquake in real time.

This way, researchers can choke the water as soon as it shivers too much and repeatedly prescribe rest periods for the soil. This makes it more complex and expensive than the classic method, which involves randomly pressing into the rock. According to Bohnhoff, however, it would greatly increase acceptance.

In Hamburg, on the other hand, it shows how big surprises on the subway can be. Initial analyzes have shown that there is more than expected. Already at 1300 meters there is a layer of rock that could contain thermal water with a temperature of up to 60 degrees. This could be heated to 80 degrees Celsius using heat pumps. Hopefully, they want to harness the deep heat in two heights from 2024. Thomas-Tim Sävecke says: “We are a model for other initiatives in the north. And throughout Germany”.

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