Store cheap heat for the winter

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The tunnels of the small mines - here an example of a museum mine - were simply
The tunnels of the small mines - here an example of a museum mine - were simply left behind after they were abandoned. They collapsed and are full of loose rubble that is permeable to water. RUB, Marquard

The waste heat from cooling generates a lot of heat in summer - when nobody needs it. It could be stored underground until winter and then used for heating.

Ruhr-Universität Bochum produces a huge amount of waste heat that currently simply escapes unused: server rooms and laboratories have to be air-conditioned all year round, the combined heat and power plant alone has two cooling towers, and that’s not all. "An incredible amount of energy is wasted," says Tobias Licha, Head of the Hydrogeochemistry working group in the Faculty of Geosciences at Ruhr University Bochum. Wouldn’t it be nice if we could save all this energy until winter and then use it for heating? This vision is what drives him. He is collaborating with Mathias Nehler from the Fraunhofer Institute for Energy Infrastructures and Geothermal Energy IEG on the WINZER project, short for "heat storage in the mines of the Ruhr region". Rubin, the science magazine of Ruhr-Universität Bochum, reports on the project.

Investigating potential and challenges

Since 2022, the project team has been working on using the former small mine below the Fraunhofer IEG campus as a natural hot water bottle. The principle is simple: mine water is extracted from the colliery, heated via heat exchangers using waste heat or solar energy and pumped back into the old, unused mine shafts. Here it heats the surrounding rock, which can store the heat for a long time. If the heat is needed for heating in winter, the warm water is taken out of the mine and the heat is extracted again via the heat exchanger.

Before the researchers attempt to store heat in the mine, they want to examine the expected potential and the possible challenges that the process could entail. Mathias Nehler examines rock samples to see how they behave when they are heated and cooled cyclically. Tobias Licha looks at what happens to the coal residues that are still stored in the mines. Samples are rinsed for weeks in the laboratory and the water is then analyzed in detail. Do pollutants dissolve? What about bacteria?

Heat for an average household to be stored by 2024

The very first tests to bring hot water into the mine took place in summer 2023. Next spring, the researchers will start pumping hot water into the mine earlier. Their initial goal is to feed in 35 megawatt hours in 2024 on a trial basis, which is roughly equivalent to the annual requirements of an average household.

Both researchers are convinced that such tailor-made, innovative solutions at the neighborhood level will play an important role in the energy transition. "We are already looking at the Dannenbaum colliery under the Mark 51°7 site, where the conditions are different, but our results can be transferred to it," explains Mathias Nehler. And there are so many mines and industries in the Ruhr area that produce waste heat that the concept seems promising for many locations.

You can find a detailed article on the topic in the science magazine Rubin with a focus on "Ice cold". The texts on the website may be used free of charge for editorial purposes, provided that the source "Rubin - Ruhr-Universität Bochum" and images from the download area are cited and the terms of use are observed.