Harnessing the geothermal potential of Scottish mine water
03 Sep 2024 • 4 minute read
Work is underway in Scotland to explore using water in abandoned mines as a reliable source of heat and energy storage.
Geothermal heat offers a possible solution to the challenge of weather-dependent renewable energies - and its viability is being assessed in Scotland.
Until recently, heating-based decarbonisation efforts have included the roll-out of heat pumps and the growth of heat networks. Now, geothermal mine water in disused Scottish mines is being explored as a potentially significant resource, with researchers and demonstrator projects investigating how best to harness this.
Untapped geothermal heat resources in Scotland
If geothermal resources are developed as planned, former mining towns could be key industrial centres once more.
In Scotland, the Midland Valley contains 600 cubic kilometres of disused mine workings. These water-filled mines could hold nearly 8,000 petajoules of untapped heat, according to research by the UK Coal Authority. This could provide 40% of the heating needed in Glasgow – or 8% of the total demand across Scotland. Achieving figures like this would make Scotland a world leader in the sector.
Water temperatures in mine shafts less than 200 metres deep are normally between 10°C and 25°C. Heat pumps can be used to extract heat and boost temperatures, with hot water then circulated to properties. Another loop returns the water to its source, where it is reheated and the cycle repeats.
Using mine water for geothermal energy storage
As well as generating heat, flooded mines can store thermal energy that would otherwise go to waste. Wind turbines in particular have a peak generation capacity and have to be turned off when this is reached.
The STEaM thermal storage project aims to use mine water to store excess energy with seasonal consistency.
The project is led by Professor Zoe Shipton from the University of Strathclyde. Shipton also led the HotScot project, which united academics, local government, industry, and the social sector to reuse old Scottish mines.
Geothermal storage potential in Scotland
There are 177,000 known mine entries in the UK. Investigations by STEaM aim to establish the impact of heat cycles on the structural integrity of mines. If 1% of mines held 20,000 cubic metres of water, this could heat 10% of UK homes during a worst-case weather week.
The project focuses on whether mine water temperatures of 55°C are safely achievable and sustainable. At this temperature, researchers believe that heat pumps would no longer be necessary between the mine and customer. As a result, the load on the electrical grid would be lower and more stable.
STEaM plans to conduct experiments at a physical site in 2024 and 2025. The team will analyse the mine water’s chemical makeup before and after heat injection. Researchers are committed to ensuring chemical reactions do not negatively impact the environment or the established heat network.
Reusing heat from the dance floor
Another Scottish geothermal innovation is at a nightclub in Glasgow. TownRock Energy is a Scottish geothermal start-up responsible for the innovative BODYHEAT system. The project stores heat from dancers at Glasgow’s SWG3 venue in 12 U-shaped boreholes located 200 metres underground.
Heat pumps powered by renewable energy extract heat from the dance floor for storage. The system then uses the heat to warm or cool the building to the desired temperature.
The project was developed with funding and support from the Scottish Government, UK Community Renewal Fund, and William Grant Foundation.
According to Townsend, the project’s success has attracted international interest from a variety of sectors.
“TownRock Energy has received an abundance of enquiries from all over the world thanks to the global media attention over the past two years, not just from venues but also from diverse customers such as data centre operators and farmers,” he adds. “We are working on rolling it out, and some of the main challenges include retrofitting existing buildings, permanency of building use and ownership.”
Support for Scottish geothermal projects
Legislation regarding geothermal heat ownership is in development in Scotland. The country’s expertise in the oil and gas industry offers transferrable skills, including corrosion management and underground modelling.
The British Geological Survey’s Glasgow UK Geoenergy Observatory has 12 boreholes and 319 advanced sensors for testing mine water. Chemical and environmental changes can be studied in water depths between 16 metres and 199 metres. Data from the site is free to access.
Industry specialists, academics, and public sector organisations can all use the facility. “It is an amazing platform for experimentation, and for validating new products such as sensors,” comments Shipton.
The Mine Water Geothermal Resource Atlas is another useful tool. It maps over 370 square kilometres of mine sites for potential geothermal development.
Funding for geothermal projects in Scotland
There are several financial support options for heat projects in Scotland. Scotland’s Heat Network Fund has a total pot of £300 million. In addition, the Green Heat Innovation Support Programme from Scottish Enterprise holds around £17 million.
The recent readmission of the UK into Horizon Europe offers another funding opportunity. Scottish Enterprise has been helping green energy companies to apply for grants from the initiative.
“If we can sufficiently research those first few projects and allow the academics to get in and pull apart some of the issues and demonstrate things such as how to model where the heat goes, how to monitor the water chemistry and develop mitigation measures for the unlikely event of problems – all of that will really help unlock the potential of the industry,” adds Shipton.
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