More than half of the UK’s electrical power was supplied by renewable energy on February 25 2026.
That consisted mainly of solar, wind and hydroelectric sources. The next day, a new source of electricity started feeding into the grid for the first time – geothermal power.
At a site near Redruth called United Downs, in Cornwall, a company called Geothermal Engineering Ltd has started producing geothermal electricity.
To generate power (electricity), this project is using two of the deepest wells ever drilled in the UK – down to three miles beneath the surface. A considerable feat of engineering.
To understand why the Cornish landscape is so suitable for geothermal power, imagine life on Earth roughly 300 million years ago, when magma from deep beneath the Earth’s surface cooled to formed large bodies of granite. This igneous rock with a crystalline structure contains small amounts of naturally radioactive elements, such as uranium, thorium and potassium.
Over a long geological timescale, these give off heat. Geologists call this a “granite‑hosted geothermal system”. Fractures throughout this granite provide pathways for fluids to flow. This is key to harnessing the thermal energy (heat) from within these rocks.
To exploit the heat in the rocks, Geothermal Engineering Ltd has drilled two angled wells. The production well reaches a depth of approximately three miles, intersecting an area known as the Porthtowan fault zone. This well produces hot fluid, at over 150°C. The vapour from this fluid is used to turn a turbine to produce electricity. The second well, drilled to a depth of almost 1.5 miles is used to inject the slightly cooled fluid back into the ground after it has passed through the turbine.
Unlike wind and solar which are weather-dependent sources of renewable energy, geothermal is always “on”. Geothermal heat is not susceptible to changes at the surface – and this means it can produce power steadily, day and night, all year round.
The deep geothermal power plant at United Downs will produce approximately 3 megawatts (MW) of electricity, the equivalent of enough power for 10,000 homes. This will meet only around 0.01% of the UK’s electricity demand. But capacity isn’t the only consideration. We need to look beyond the capacity to understand the full picture and future opportunity.
First, there is the cost of generation. Geothermal, like other renewable sources, has lower operating costs compared with traditional gas power, however the upfront costs for developers and investors are high. The cost of electricity from wind and solar has fallen significantly over the past decade. Geothermal is just at the start of its cost reduction journey. As the potential for reduced drilling time and costs increases, the scale up of geothermal could become more affordable.
Then there is the wider grid benefits. As the UK grid will rely more heavily on wind and solar in the future, it will require much more flexibility. Any source that is less susceptible to variability in energy generation can better match supply to demand. This makes it easier to incorporate other less consistent renewable sources into the grid.
While the capacity of some geothermal power plants such as United Downs is not comparable to the scale of an offshore wind development or a nuclear plant, they can deliver meaningful grid support, resilience and, in particular, benefits for consumers. For example, the UK government’s planned expansion of AI and data centres could further increase electricity demand; cooling them alone currently accounts for about 40% of a data centre’s electricity use, so matching them with local sources of energy makes sense.
While electricity production is the primary goal, United Downs will also produce lithium, a critical mineral that is essential for batteries. Fluids at depth contain relatively high concentrations of lithium. Locally sourced lithium can help reduce the UK’s reliance on importing sources.
The future outlook
Geothermal Engineering Ltd is currently developing two other sites in Cornwall. These could deliver a further 10MW of geothermal power in the UK by 2030. Recent estimates suggest that the eventual resource potential for electricity from geothermal is around 25GW nationally – roughly 2.5 times the contribution that wind currently provides.
However, it took wind more than 25 years to scale to 30GW of installed capacity in the UK. So perhaps the most pertinent question isn’t a geological one, but rather a question of economic feasibility: can geothermal electricity compete on the same scale and cost as other options for low-carbon electricity?
Looking beyond power generation, several recent reports, including work commissioned by Department of Energy Security and Net Zero shows that geothermal can be a significant low-carbon source of heating and cooling. Resource estimates for heating and cooling are more than 100 times greater than the estimated electricity generation potential. Geothermal heating can help address the cost of heating and greenhouse gas emissions associated with natural gas.
This single development in Cornwall, or even a small number of other projects, probably won’t change household electricity bills in the near future. However with gas still setting the price for electricity in the UK, the cumulative potential for geothermal energy to complement other renewable energy sources and deliver energy that could reduce this reliance is considerable.
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