Realising the UK's geothermal potential

Manchester researchers are working to support the UK’s net zero targets by determining the potential of the Carboniferous Limestone for generating geothermal energy.

Exploring geothermal energy’s potential in the UK

Geothermal energy has the potential to support the UK’s net zero targets, by providing a sustainable future source for heating and cooling, particularly for agricultural and domestic buildings, but also public facilities such as swimming pools.

Currently, the lowlands of the Netherlands, Belgium and Germany have working geothermal systems from the same geological strata. Now, Manchester researchers are working with the British Geological Survey and University of Bristol to explore whether this potential can be realised in the UK.

Professor Cathy Hollis, Chair of Carbonate Geoscience at The University of Manchester, explains: “Geothermal has not made the headlines in the UK as a source of renewable energy like wind power because it’s a very young industry here. Over the last ten years it’s been talked about a lot but now’s the time to explore its potential at pace.”

Could Carboniferous Limestone be the solution?

One source of geothermal energy comes from the Carboniferous Limestone, which is a major bedrock in the UK. It dominates the White Peak area in Derbyshire and much of the landscape across the Yorkshire Dales, Pennines, southern Scotland and southwest England and Wales. It also sits in the subsurface beneath most of central UK cities, including Manchester, Sheffield, Nottingham and Bristol.

In England, the Carboniferous Limestone is a major aquifer for shallow water supply, and naturally supplies geo-thermal water, heated to around 20-40 °C, such as in Buxton, Matlock Bath and Bath Spa.

With opportunity comes challenges

While the Carboniferous Limestone’s abundance in the UK shows opportunity, there are two key challenges: firstly, although Carboniferous Limestone exists underneath most cities, it is not present everywhere. Secondly, the ability of the rock to sustain the flow of warm or hot water is uncertain.

One aspect of the rocks that might help to maintain fluid flow from depth are caves, which intersect to provide pathways for warm water. Networks of deep, often vertical caves that cut through the subsurface may help to make geothermal a viable option for the supply of heat, by delivering sufficient volumes of hot water from depth. Because of the depth of the limestone, the water would be hotter than the sub-40- degree temperatures measured in natural hot springs.

Professor Hollis explains this is not the only option: “At Manchester, our community is looking at multiple options, so if geothermal doesn’t work in Carboniferous Limestone, we’re already looking into the potential of mine water, deep sandstone aquifers and the reuse of old oil and gas wells to supply geothermal water.”

Supporting the UK’s net zero targets

In a project funded by The Natural Environment Research Council, and in collaboration with the British Geological Society and the University of Bristol, Manchester subsurface experts are determining where these caves form, and why. Answering these questions, as well as the crucial question of when they were formed, will establish whether they are present at depths of two-to-three kilometres beneath the Earth’s surface. This is the depth required to be an effective future heating source and will help to predict the role that the Carboniferous Limestone will play in the UK’s geothermal future.

The project, currently in its first year, consists of two distinct phases: characterisation of the rock to build a geospatial map of caverns (focused on the White Peak of Derbyshire) and building
models to understand how these caverns form.

“Geothermal in the UK has a lot of potential to supply hot water for heating. Using our subsurface expertise, we’re driving decisions on how best to leverage that potential,” says Professor Hollis.

The research findings will contribute to an ongoing evaluation of the ability of the Carboniferous Limestone to produce geothermal heat, and could lead to future investment in deep geothermal technology in the UK.