Mine water geothermal heating - Can coal mines warm our houses again?  

There are about 23,000 mines in the UK, most of them are coal mines. Many towns were built, or grew, because of the mining industry, and therefore around one in four homes in the UK is built more or less on top of a mine. Unlike places like Iceland, the UK thermal gradient is modest, only 20-30 degrees per kilometre. So typical water temperature in those mines is only 12-25ºC: with the deeper ones a bit hotter than shallower ones. These temperatures are not high enough to use directly, but using heat pump technology this heat can be used to provide much warmer water of 40-50ºC. 

So we clearly have a huge resource below our feet. But to use it efficiently, we have a few challenges to overcome, including:  

• extracting the heat from the ground; 
• storing heat so that we can better deal with seasonal fluctuation of heat demand;
• social acceptance of mine water heating; 
• a fair and affordable energy transition for everyone; 
• creating a suitable regulatory framework for this relatively new heat source.  

 Many of these challenges are related, and if we want to successfully use mine water heating as a clean heat source in the future we need to overcome each one of these challenges.

Working towards a solution

 This is why, during the Covid lockdown period in the summer of 2020, a team at the Durham Energy Institute at Durham University, together with colleagues from the British Geological Survey, decided to set up the GEMS research project (GEMS stands for Geothermal Energy from Mines and Solar-geothermal heat), for which we managed to attract external funding. GEMS forms a very multi-disciplinary team of Earth scientists, engineers, anthropologists and economists, and benefits from knowledge and data provided by a wide range of project partners, including local and regional businesses, national and international industrial partners, the North-East mining institute, and Durham County Council.  

 Since the project started in the Autumn of 2021, we have made a lot of progress. A team in the department of Earth Sciences at Durham, including academic staff, postdoctoral researchers, postgraduate students and undergraduate students, worked together to develop the GEMSToolbox modelling tool (Mouli-Castillo et al., 2024). The GEMSToolbox can predict the feasibility of mine workings to extract heat, and can also determine the longevity and thermal power output of such mine water heating systems (Figure 1).  

Figure 1: Example of mine water geothermal heating potential modelling using the novel software tool GEMSToolbox (Mouli-Castillo et al., 2024)². Mine water is extracted from the deeper mine, and heat is extracted using a heat pump. After that, the water is re-injected into the shallower mine and flows through the mine workings back towards the abstraction point, which allows it to warm up again. 

 A group of researchers in the Department of Engineering at Durham University developed a novel technique to effectively store heat to overcome fluctuations in heat demand (Koley et al, 2024). They investigated the potential of using commercial silica gel as an energy storage material in a bulk-scale open bed adsorption-based system, to achieve efficient domestic heating using renewable energy sources. 

 Researchers in the department of Anthropology established how end users view mine water heating and the clean energy transition, and how such a transition could be achieved by collaboration between local councils, industries and end users. A team at the Durham Business School established what people value most when transitioning to renewable energy, requesting information from over 1000 people in North-East England using choice cards.  

The next step in the journey towards widespread, successful mine water heating schemes is to apply these GEMS tools and knowledge to the development of new mine water heating schemes, to recognise the remaining obstacles, and to use our research knowledge to provide a solution. Mine water heating is still not yet widely applied in the UK, and doesn’t yet have the same level of documentation, information supply and stakeholder network that other renewable energy solutions, such as wind or solar-PV energy, now have. The GEMS team is working with local councils, regional industries and government bodies to enable mine water heating on a wider scale in the next decade.  

References: 

• Mouli-Castillo, J., J. van Hunen, M. MacKenzie, T. Sear, C. Adams, GEMSToolbox: A novel modelling tool for rapid screening of mines for geothermal heat extraction. Applied Energy, Volume 360, 2024, https://doi.org/10.1016/j.apenergy.2024.122786
• Susmita Koley, Huashan Bao, Anthony Paul Roskilly, Zhiwei Ma, Experimental parametric evaluation of adsorption characteristics for silica gel - water based open-bed system for seasonal thermal energy storage, Journal of Energy Storage, Volume 89, 2024, 111812, https://doi.org/10.1016/j.est.2024.111812