The UK’s geothermal potential has been known for decades. While high cost and fears over its connection to seismic activity have historically made investors wary, a new push for the resource is on the horizon. BGS researchers joined geologists from across the country in a report published in Petroleum Geoscience, which urges energy providers to turn their focus to this untapped resource, labelling geothermal energy, carbon capture and storage, and bioenergy with carbon capture and storage as ‘critical’ to moving the UK towards its target.

Yet further groundwork is necessary before geothermal can reach its full potential, with research needed into the country’s subsurface to better understand its resources and properties. Even with this information, there are still those who maintain the energy source can only cater for a small portion of the country’s power needs. So what does the geothermal landscape actually look like in the UK?

The push for geothermal

“The UK has lived through an era of cheap gas, used extensively for heating,” says Dr Jon Busby, a Geothermal Specialist at the BGS. “This originally came from the North Sea, but with the depletion of this energy source and the requirement to decarbonise, there is an urgent need to replace natural gas.”

Previous geothermal projects have failed to get off the ground due to financial issues, yet reasons to pursue the resource remain as strong as ever. Dependent on a more consistent source than that of solar or wind, geothermal plants operate more than 90% of the time and use far less land per MW than other renewables. As the BGS report says, with 99.9% of the planet at a temperature greater than 100°C, geothermal is a renewable resource with great potential.

“Geothermal energy for heating can play a major role,” says Busby “sourced either from deep sedimentary aquifers where the water is hot enough to be used directly for heating, or from shallow ground source heat pumps.”

“Much of the technology used for geothermal heating is mature,” he adds, “but research is required to apply the technology to UK geological conditions. There are risks involved in drilling boreholes to access deep geothermal resources and these risks need to be quantified in order to attract investment from the energy sector. Geothermal power requires drilling boreholes to intersect deep fractures but the nature and orientation of these fractures is not sufficiently understood for the rapid adoption of this technology.”

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Geoenergy Observatories are under construction in Cardiff, Glasgow and Cheshire – commissioned by the Natural Environment Research Council to gain insight into the UK’s subsurface. Information gathered from the sites will help to inform the development of geothermal technologies, with the sites in Cardiff and Glasgow looking specifically at shallow geothermal. Such research is seen as the only means of seeing the energy source rolled out on a wider scale, and Busby says this type of research “provides the data needed for the planning and development of future schemes.”

Where is the technology currently being used?

On the matter of where we should look to install geothermal plants, Busby says while ground-source heat pumps can be installed almost anywhere, not all regions are suitable for deep geothermal.

“Direct use of deep geothermal waters for heating requires rocks at a depth from which water can be abstracted and reinjected after use,” he says. “Geothermal power generation requires temperatures of 160 degrees centigrade or more at depths which are not too deep, as otherwise the drilling costs are too high. At present this is restricted to regions where high heat producing granites occur within the crust.”

From these specifications, the southwest of England is the most favourable region. Cornwall in particular is a prime site for geothermal activity, with one study showing the county’s extensive granite could provide a fifth of the UK’s power if harnessed correctly. A geothermal power plant is currently under development at United Downs, where two wells have been drilled into a fracture zone. Later installation of a 1-3MW power plant is expected if circulation testing proves successful, with predictions indicating the plant could reduce greenhouse gas emissions by more than 3,000 tonnes per year, as compared to conventional generation.

The Eden Geothermal project is also now underway in the region. The industrial research project will drill a 4.5km deep well at the Eden Project, used to heat its biomes, greenhouses and offices in the first leg of a two-step project.

Are there any limitations?

A report by the International Energy Agency, while applauding the UK’s decarbonising efforts, advised the country to maintain its focus on oil and gas as leading energy sources. The agency supported the continued imports of these fuels in addition to the extraction of any remaining domestic reserves, saying that the resources would likely remain a crucial part of the country’s energy mix. Similarly, Busby said that even with the required research into geothermal, it is likely to be limited to use on domestic, local levels.

“Geothermal power is unlikely to ever generate more than a few percent of the UK’s requirements,” he says, “but it can contribute to local, sustainable green energy solutions.”

This is not to underestimate the value of geothermal on a small-scale level. A prime example of its benefits can be seen from the BGS project in Cardiff. Here, a pilot groundwater heating scheme examined the use of geothermal to heat a school building, with the Urban Geo Observatory collecting data from the project. Although there were physical limits on the amount of water and heat that could be extracted, overall findings showed that even a small amount of heat from the reserves could provide a low-carbon heating solution. The researchers say this could be applied district-wide in both homes and commercial buildings.

While it seems geothermal remains too site-specific to be rolled out on a nation-wide level, findings from the BGS indicate that the resource could still bring significant benefits to the UK, and with the right research in place the country could gain a leading spot in this budding global industry.