By Anthony Harrington
A current study by the British Geological Society (BGS) into how groundwater in former mine workings could be used to drive city-scale district heating systems has the potential to transform the way Scottish households and businesses heat 
their homes.
David Schofield, science director for energy systems at the BGS, explains that if there is a sufficient flow of groundwater into and through old abandoned mine workings, then it could be feasible to extract some of the heat out of that groundwater to drive a district heating network.
Research into the geothermal energy within these flooded mines could turn this redundant resource into a clean heating source. Schofield points out the magnitude of possibilities for reducing fuel poverty and developing resilient communities: reminding us that much of the UK’s urban population growth over the last 200 years took place above coal seams where the essential fuel to drive industrialization was being mined.
Interest in geothermal energy has been growing as a part of the renewables mix. In 2013, the government published a study into the potential for deep geothermal energy in Scotland, pointing out that virtually all geological formations in the UK have the capacity to store sufficient heat to support the use of small-scale (closed loop) ground-source heat pumps (GSHP) for heating purposes. 
For most of the UK, groundwater temperatures at readily accessible depths – up to 100 metres underground – are at a stable temperature of around 10 to 12°C. This could rise as high as 20°C in some of the UK’s abandoned mineworkings.

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Schofield explains: “While the mines were being worked, groundwater, which naturally seeps into mine shafts and tunnels, was continuously pumped out. In an abandoned mine, the groundwater fills and flows through the workings. This underground water is at a relatively constant temperature and has the potential to act as a heat source for district heating scheme. Research is needed to understand that true potential.”
To this end, some years ago, the BGS sought to establish an observatory site that would provide continuous long-term monitoring of the chemistry, microbiology, fluid flow, heat displacement and replenishment with the flooded mineworkings. 
The observatory would provide research boreholes, monitoring equipment and a comprehensive dataset available to academics and engineers to deliver independent analysis of the geothermal environment of the coal mines.
After a successful bid for a government-funded investment into the research required to bridge the science and technology gap, in 2017 the Department for Business, Energy and Industrial Strategy (BEIS), made £31m funding available.
The £31m will fund two observatories: the UK Geoenergy Observatories. A £9m observatory proposed for the east end of Glasgow will establish the Glasgow Geothermal Energy Research Field Site: to take forward research into the shallow mineworkings below Dalmarnock. 
A £15m observatory in Cheshire will establish the Cheshire Energy Research Field Site, which will look at the geological environment for all energy technologies. The remaining funding is invested in the infrastructure required to operate both sites.
At present, Schofield says, there are very few large scale district heating systems that utilise groundwater in abandoned mineworkings and the Glasgow Geothermal Research Field Site will tell us so much more about the potential of flooded coal mines to a sustainable heat source for the future.
He explains: “There is a scheme in the Netherlands, at Heerlen, which takes heat from flooded coalmine workings that has been operational since 2008. The current phase of the project provides heat to a few businesses in the area and they are looking to expand it. 
“However, the Heerlen district heating network does not rely solely on GSHP and the abandoned coalmine. They are also exchanging ‘waste’ heat from buildings within the system. 
“There are some real constraints when it comes to rolling out these kinds of heating systems. The initial capital costs are high. We are still trying to work out answers for questions like what is the optimum size of a district heating network based on a GSHP system drawing on the heat in mine water. This is one of the issues that the research community is likely to consider.
“We have a team at the BGS specialising in geothermal research for some 30 years. In that time we’ve amassed knowledge of both deep geothermal energy resources as well as the potential for ground source heating the UK.
“However, it is all work in progress, aimed at providing the evidence that will inform the public debate about the viability of large-scale district heating based on GSHP technologies. 
“Ultimately, we are trying to facilitate the growth of these kinds of clean energy heat sources as part of Scotland and the UK’s decarbonisation of their energy systems. Abandoned mine workings look like a very promising approach.”
Schofield believes that geothermal solutions have a very clear role to play in Scotland’s approach to moving to low carbon heating.
“If we can move Scotland away from its use of natural gas for domestic heating and cooking, that will help enormously. However, the capital expenditure for shallow geothermal heating is a real stumbling block likely to need both technical and financing solutions,” he concludes.