Heating and cooling both make up a large part of the total energy demand in the UK; long-term seasonal thermal energy storage (STES) can address temporal imbalances between varying supply and demand of heat to buildings and processes. Underground thermal energy storage (UTES) can play a role in energy decarbonisation by storing waste heat from space cooling, refrigeration, data processing, industrial processes, harvested summer solar thermal energy or even heat generated by surplus renewable (solar or wind) electricity with fluctuating supply. This paper evaluates a range of UTES technologies in a UK context and addresses geological suitability, storage capacity, low-carbon heat sources, surface heat sources and demand. This review concludes that there is a significant potential for UTES in the UK for both aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES) systems, coinciding with surface heat sources and demand. Therefore, uptake in UTES technology will help achieve net-zero carbon neutral targets by 2050.

There is also scope to utilise UTES technologies within existing subsurface infrastructure. There are 464 oil and gas wells which could be repurposed upon end of life using different UTES technologies. However, the potential for repurposing needs further evaluation; deep single well BTES systems will have a high surface area to volume ratio for storage, reducing the efficiency of such systems and the potential for ATES is limited by issues associated with contaminants. 23,000 abandoned mines underlay ∼25 % of the UKs population and could be utilised for minewater thermal energy storage (MTES).