Heat production accounts for 45% of energy use and 32% of CO2 emissions in the UK, but its decarbonisation is far more challenging than transport or power due to decentralised generation and consumption, overreliance on fossil fuels and dependence on seasonal and weather conditions. To address this challenge, the UK needs robust and scalable thermal energy storage infrastructure, both for balancing of renewable heat generation and the capture of waste heat from processes such as power generation and waste incineration. Storing excess heat to meet long-term seasonal and diurnal demand would promote clean, sustainable energy use and help overcome a significant barrier for reaching Net Zero carbon emissions. Thanks to our industrial past, the UK has vast subsurface heat storage capacity. Flooded coal mines contain enormous volumes of water (>75 billion m3 nationally and ≤ 2 - 4 million m3 per mine) and lie under 25% of all UK homes. Heat can be injected to mine water via heat exchangers in summer (or day-time), and then extracted and upgraded using heat pumps in winter (or night-time). However, thorough investigation is required to establish mine void architecture and understand thermal behaviours within mine water systems.
This project aims to determine the technical feasibility of heat storage in flooded mine shafts, achieving this via the following objectives: (1) Comprehensive system hydro and thermo geological characterisation; (2) Predictive simulations of diurnal and interseasonal storage; (3) Modelled integration of storage solution(s) into an energy network. It will also assess the potential engineering risks and environmental impacts of such activities.
In partnership with the Coal Authority (TCA), we will use the Monktonhall (Midlothian) site, which will host a district heating network for 4,000 homes, as a case study. TCA will supply legacy mine data and provide access for detailed site investigations which will include in situ physicochemistry measurements and sampling of water and shaft lining materials for lab assessments (including chemical and thermal properties). This data will parameterise predictive simulations which will assess store thermal behaviour in response to variable scenarios for: (A) resource availability and demand; (B) long and short term time durations and (C) heat exchange and injection and extraction strategy. Once optimal operating conditions are established for selected scenarios, simulation outputs will be integrated into a wider energy network model to assess the efficiency of mine water thermal energy storage for balancing heat supply from the multiple (and variable temperature) renewable and waste heat sources that will likely contribute to future low-carbon heating networks.
References:  The Coal Authority (2018). Clean energy from the coalfields, Mining the Future 2018.  Banks, D. , Athresh, A., Al-Habaibeh, A. and Burnside, N. (2019). Water from abandoned mines as a heat source: practical experiences of open- and closed-loop strategies, United Kingdom. Sustainable Water Resources Management, 5(1), pp. 29-50.