Mine water as seasonal heat storage in urban regions—a case study for Freiberg (Germany)

Abstract Seasonal heat storage has been studied in Germany for over 30 years, but to date only a few pilot plant facilities have been built, such as those for borehole geothermal energy storage, pit storage or aquifer storage. A promising yet underutilized approach is the use of abandoned, groundwater-flooded mines for thermal energy storage. These offer high storage capacities due to their large volumes and extensive contact surfaces with the surrounding rock. Since cities often develop near mining sites, this could present a viable solution for energy supply in urban areas. A feasibility study in the city of Freiberg investigates the suitability of a former silver mine for this purpose. The storage efficiency depends on geological and thermal conditions, such as the accessible mine volume, water flows, and temperature limits. Initial results show that storage efficiencies of 50–60% can be achieved. Based on the city’s structure, four potentially suitable districts were identified. The “Bahnhofsvorstadt” district is examined in more detail. Here, it becomes clear that the integration of industrial waste heat is crucial for economic viability. In certain scenarios, the system could achieve amortization within ten years. Depending on the scenario, fossil fuel consumption can be reduced by over 50% and the district can be self-sufficient for around nine months of the year.