THE POTENTIAL FOR GIGAWATT-HOUR SUBSURFACE THERMAL ENERGY STORAGE IN MINE SHAFTS

We examine the use of abandoned mine shafts for interseasonal storage of curtailed wind energy in the form of heat. In 2020, UK wind curtailment payments were £282M: enough to power 1.25 million homes: equivalent to £4 per MWh. Surface engineered thermal stores are currently limited by size and the need for insulation, and the thermal storage opportunity within flooded mine shafts is substantial. If heat generated using curtailed wind can be safely stored in mines, then utilising 1% of UK mine entries could potentially provide heat for 10% of UK homes during a ‘worse case weather week’ (cold, still winter days, when heat demand is highest). This requires heating the shaft water to 55 degrees centigrade so that it can be used directly, eliminating the electrical demand for heat pumps. Here we examine the implications of temperature cycling within the shaft for mineshaft stability, geochemical evolution of the water within the shaft, heat and water flow in the rock mass around the shaft, and the wider energy system demands. Finally, we outline our experimental heat injection planned for 2024 at an abandoned mineshaft site in Scotland.