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

This is the authors' abstract. We don't add key points for this paper.

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 <10% heat losses relative to input energy, whereas seasonal operation results in substantially higher losses. When integrated with heat pump networks, the system reduces levelised heat costs by up to 2.5 p/kWh with a 20 p/kWh charging-tariff differential. Although results demonstrate promising performance under certain operating regimes, further investigation is required. This work also forms part of a wider project evaluating shaft suitability, long-term structural stability, water chemistry, fluid dynamics, new-build shaft options, and practical system configurations.