Germany is looking for new sources of energy – the Ukraine war clearly shows the dependency on imports of fossil fuels. A promising alternative: geothermal energy. In order to use the potential in this country, research is currently being carried out with new high pressure.
There is great potential for the energy system slumbering deep beneath our feet: geothermal energy. With every kilometer underground, the average temperature rises by 30 degrees Celsius. “Since the formation of the earth, part of the heat has been generated continuously through the decay of natural radioactive isotopes. Today this is increasingly taking place in the earth’s crust,” says Eva Schill. She heads the Geoenergy Cluster of the Institute for Nuclear Waste Management (INE) at the Karlsruhe Institute of Technology (KIT). The heat slowly but surely rises to the earth’s surface, from there it goes into the atmosphere and then escapes into space. On the way out, just a tiny fraction of it could be enough to warm our homes and power our industry.
The easiest way to do this is with hydrothermal geothermal energy. Today, boreholes are drilled about three to five kilometers deep underground and reservoirs with hot water are tapped. This is pumped to the surface, gives off its energy via heat exchangers and is then fed back into the subsoil. “We published a roadmap together with the Fraunhofer Society,” says Eva Schill. “There we showed that we can cover around 25 percent of Germany’s heat requirements with hydrothermal geothermal energy. That’s around 300 terawatt hours.”
However, the conditions for hydrothermal geothermal energy are not the same everywhere in Germany. The corresponding reservoir rocks are essentially limited to the sedimentary basins in northern and southern Germany. That is why the scientists also want to use the crystalline basement. “We then call this petrothermal geothermal energy and it is much less location-dependent,” explains the researcher. “However, the development of the crystalline basement for geothermal energy is a completely different technological challenge.” Because the rock is usually very dense. So there is little water.
But there are certain areas, tectonic fault zones such as in the Upper Rhine Graben, where thermal energy could still be tapped economically with technical measures. “But these measures are associated with technical challenges. For example, they can lead to induced seismicity,” says Eva Schill. “In the past, vibrations were generated artificially in this way.” In order to solve such problems, the project accompanies the construction of a new research infrastructure. Together with the Helmholtz Center for Environmental Research (UFZ) and the Geoforschungszentrum (GFZ), the Geolab underground laboratory will be set up over the next few years under the direction of the Karlsruhe Institute of Technology. At medium depth, the three Helmholtz centers want to investigate how the problem of induced seismicity can be reduced.
However, induced seismicity and technology development are not the only challenges facing the widespread deployment of geothermal energy. “Aside from the provision of base load heat, a major problem in heat supply is covering the middle load in the seasonal transition periods,” the geologist points out. “We also want to keep the underground system as stable as possible, because any change in temperature or pressure can lead to the precipitation of minerals. This means that the dissolved salts crystallize and impede the flow of water. This impairs the functionality and efficiency of the systems.” However, continuous operation leads to excess heat, especially in summer. Of course, you could generate electricity from it. But you could also store it and use it for heating in winter.
This is exactly the path Eva Schill is taking. “We want to use porous rock underground to store the excess heat there.” In order to research such pore storage in more detail, KIT is currently building a research infrastructure on its own campus. The place is well suited. Because under the KIT there is an old oil reservoir. This should now store heat in the form of hot water. “We already have heat storage that works well at low temperatures. A good example here is the Reichstag in Berlin,” says Eva Schill. “But in the future we also want to supply the district heating networks with heat via these storage systems. Most of these work with flow temperatures of over 100 degrees Celsius.” And there is still a need for research in this temperature range.
You have to know that the higher the temperatures and pressures, the higher the probability of changes in the subsoil. This is primarily due to the salts that are dissolved in the natural deep water. If the conditions change, they fail and clog the pores of the storage tank. “For us, this is a lighthouse project that is already part of the normal Helmholtz program funding,” says Eva Schill. “Originally, we wanted to achieve a technology readiness level of 5 to 6 by 2027. With the funds from the current acceleration funding, we hope to be there by 2025.”
However, pore storage tanks cannot only absorb hot water. Hydrogen, which is expected to play a key role in the energy transition, can also be stored in the spongy rock. And this is Eva Schill’s second lighthouse. “Of course, the existing natural gas storage caverns (caverns are artificially created cavities in salt domes, editor’s note) can be repurposed for hydrogen,” she explains. “But with a view to the federal government’s hydrogen strategy, we will need ten times more cavern storage in 2030 than is available. We must therefore also consider other storage options.”
And that’s where pore storage comes in. One fact makes them particularly interesting: the regional distribution. In order to effectively supply Germany with renewable energy, the storage systems must be distributed as evenly as possible across the country. Today’s caverns are mainly in northern Germany. Pore storage, on the other hand, can be distributed more evenly.
“With the additional funds now available, the GFZ colleagues are starting the Hyaquistore project in the North German Basin,” says Schill. “Years ago, the GFZ successfully demonstrated CO2 storage there. Now we will convert the site and carry out experiments on hydrogen storage.”
Geothermal energy combines energy with geosciences. No wonder then that the KIT, the GZF and the UFZ work in close partnership. This cooperation, which has been practiced for a long time and is very successful, is now to be bundled in the course of the acceleration project. KIT and GFZ will now lay the foundation for a “Helmholtz National Lab for Geoenergy”.
And that should advance geothermal energy well beyond research. Because one reason why it still lags behind the other renewable energies is the very high investment costs in the geothermal plants. This is high-risk capital, especially in the early days. That is why the federal government and in particular the Ministry of Economics are thinking about how to initiate these investments. “One goal of the Helmholtz National Lab is to support the federal government in this,” says Eva Schill. “All the know-how that we are now collecting with the flagship projects should go into a national pool. We want to use this to support business partners in advancing geothermal energy.”
Read more: This article first appeared on helmholtz.de.