Geothermal Utilisation of Flooded Underground Mines Based on the Example of a Mine Thermal Energy Storage

In recent decades, former mining infrastructure has been perceived primarily as a financial and environmental burden. Geothermal utilisation has so far only been implemented in a few projects. Recently, a paradigm shift has been observed in this regard. Flooded underground mine workings can repre-sent a geothermal resource, under certain circumstances, the mine water can be used for heating or cooling. Currently more than fifty mine water geothermal plants exist worldwide, most of them are located in Europe and North America and are used for heating purposes. There are two types of systems: open systems, i.e. well systems for the extraction and possible reinjection of mine water, and closed systems, using geothermal probes or pipe heat exchangers. The mine water itself is not used directly, heat is transferred to a secondary medium. Another way to utilise mining infrastructure and mine water is the seasonal storage of surplus heat. Here, the flooded mine is used as a large “geobattery”, also known as mine thermal energy storage (MTES). Surplus heat, for example waste heat from industrial processes, geothermal or solar thermal plants as well as biomass recycling, is injected into the flooded mine and heats both the mine water and the surrounding rock. During heat demand, mainly in winter, warm mine water can be pumped back up and made available for cold (neighbourhoods) or warm district heating networks. Development takes place via the existing mining infrastructure (e. g. shafts) or via bore-holes. As part of the EU-funded project “Piloting Underground Storage of Heat in geoThermal reservoirs” (PUSH-IT, grant no. 1011096566), an MTES pilot plant has been under construc-tion since 2024 at the Technical Center of the Ruhr University Bochum (RUB), Bochum/Germany. With up to four boreholes at a depth of 120 m, the abandoned and flooded “Mansfeld” colliery is currently being developed. In an isolated area (1st floor), a flooding volume of approx. 10,000 m³ can be assumed. Surplus heat from the Technical Center, such as from existing cooling towers or from the data center in the northern area of the project site, will be used. Due to the technical design of the boreholes, water with a maximum temperature of 85 °C can be pumped into the mine. Initial estimates predict that the heated mine water can be extracted at a temperature up 25 to 50 °C. Computer-assisted models will be calibrated during thermohy-draulic tests carried out as part of the project in order to verify the temperature estimations. In order to achieve optimal system integration with the Universities heating and cooling network, a co-simulation is being carried out, considering different variants of input and output quantities. For example heat pumps that could be connected to the system. In addition to the technical implementation, regulatory topcis for this new technology must be clarified. In addition, communication strategies are being developed to raise awareness about the potential of mine heat storage and increase acceptance of the reuse of former mining infrastructure. The PUSH-IT project demonstrates the feasibil-ity of underground heat storage in flooded mines and paves the way for transferring the technology to other mining regions. This article is based on the German-language version published in the proceedings of the 23rd Colloquium on Abandoned Mining of Clausthal University of Technology.