Mine water heat storage with heat pump as a solution for decarbonisation in urban areas
Around 57% of the world’s population currently live in cities, with this share exceeding 70% in Europe and 80% in North America. As urbanization continues to rise, energy demand in densely populated areas is growing, while simultaneous decarbonization of heating and cooling remains a major challenge. One promising approach is the use of abandoned and flooded mines as seasonal heat storage systems in combination with heat pumps. Many cities have developed near former mining areas, making post-mining utilization particularly attractive. In addition to surplus heat from industrial processes or solar thermal systems, excess heat from summer cooling can also be stored. The large water volumes and extensive rock contact surfaces in mines enable significant seasonal energy storage capacity. In Freiberg, Germany, a pilot-scale storage system was implemented in a former silver mine and operated continuously in test mode for over two years. Storage efficiencies between 45 % and 65 % were achieved, with a heat pump enabling the charge and discharge of the storage system. The mine water temperatures varied between 2 °C and 40 °C. Based on modelling of three potential districts in Germany, self-sufficiency levels of up to 80 % and storage durations exceeding three months are feasible. Depending on system configuration and existing infrastructure, payback periods between 10 and 15 years are possible — and below 5 years when a district heating network is already in place. These results demonstrate the technical and economic viability of mine water heat storage as a scalable component for sustainable urban heating and cooling.