Lifetime techno-economic modelling of underground mineshaft thermal storage for district heating

Conversion of existing flooded mineshafts to hot water thermal storage for heat networks offers a potential practical solution for large-scale storage without significant new sub-surface construction. We have specifically addressed the long-term thermodynamics and economics of such a system to assess feasibility. A Python model of a mineshaft has been developed that combines existing tank and ground thermodynamic modelling methods into a computationally effective means of performing multi-year analysis with sub-hour timesteps to understand system dynamics, including the long-term impact of heat transfer with the surrounding geology. The new mineshaft model, integrated into a wider energy system model, was used to investigate storage operated over a range of timescales, from intra-day to seasonal. For cost-optimal demand profiles, daily to weekly cycling achieves