Feasibility of waste heat storage in flooded coal mines

Flooded coal mines could be useful for decarbonising space heating of certain urban areas of Europe through the use of mine-water thermal energy. However, in communities with high heat demand and low groundwater temperatures heat mining and thermal depletion could occur. Storing ‘waste’ heat from sources such as data centres could counteract this effect and produce subsurface heat reservoirs. This operation was evaluated in a 3D numerical model of a flooded coal mine, through a simplified scheme of 6-month cycles of heat storage and extraction. The results show that 25–45% of the energy transferred to the subsurface could be recovered during the first year. The heat recovered could reach the energy of the coal ‘mined’ in less than 70 years of energy recycling and it could equal the coal monetary value in less than three decades. A mapping investigation of data centres in the UK evidences more than 60 prospective sites sitting above flooded mines where subsurface heat storage could be employed. One of these sites will be studied in an industrial and academic collaboration in the planned Galleries 2 Calories project by the University of Edinburgh, using the worked seams of the Midlothian Coalfield as heat transport means.