Christian M. 7 min read

Britain’s unorthodox deep geothermal plant

The UK is legally bound to reach net zero by 2050 yet is significantly behind schedule.

At the same time, offshore wind energy is the main headliner when it comes to the energy transition, and rightly so, given the UK’s ample wind resources. Yet, an unexpected tech has recently arrived on the scene, one which certainly doesn’t come to mind when contemplating the idyllic Cornish countryside.

Deep radioactive geothermal power, anyone?


What is Geothermal Energy?

Conventional geothermal power (Credit: Greenfire Energy)

Its sums it up. Geo means ‘Earth’, and thermal means ‘heat’. Geothermal Energy is the extraction of the Earth’s heat naturally present at depths.

This heat is extracted by pumping cold water underground, letting it flow through hot rocks, and then pumping it back to the surface as hot water that can be used directly for heating purposes or pressurised into vapour to turn an electric turbine and generate electricity.

Geothermal Energy is most popular in geologically ‘active’ regions where the Earth’s deep heat finds conduct into shallower depths where it can be extracted economically.

For example, Iceland is known for its extensive use of geothermal energy as it has bountiful supplies of shallow, underground heat due to its location in the mid-Atlantic ridge. This is obvious when you see its comprehensive network of hot springs, geysers and volcanoes.

Other geologically active countries with plenty of volcanic activity, like the USA, Italy and Turkey, also leverage much of this heat for geothermal projects.

However, there are exceptions to this trend, and the UK is showing the world that shallow heat can also be found in areas where you don’t expect it, and you don’t need molten magma on the surface to have geothermal potential.

Radioactive geothermal

The British isles sit on old rocks that have retired from geological duty a long time ago, bang in the middle of the Eurasian Plate, away from any major earthquake zones or active volcanoes.

Yet, some old granites in the very tip of Cornwall have such a high concentration of radioactive material that their decay alone produces enough heat to clearly show on the UK’s heat maps.

In more technical terms, the Cornish radiogenic Cornubian granite batholith is the source of this heat.

In fact, this area is the hottest in the UK and has been subject to geothermal experiments since the 1980s, although most of these were eventually shelved. It was prime time for fossil fuels, and the media’s attention was focused on the economy and the Falklands rather than renewables.

The geothermal re-birth

Grey = Radioactive Cornish Granite with vertical faults (Credit: GEL – Youtube)

A renewed interest in renewable energy in the 2000s triggered a boom in new companies and startups looking to innovate the industry. Amongst them was Geothermal Engineering Ltd (GEL), which began working on the United Downs project in 2009 to re-explore deep geothermal power in Cornwall.

The team set out to continue on from the Cornish Hot Dry Rocks (HDR) project that was stopped in the 1980s that demonstrated the viability of a deep geothermal project using the faulted zones within the hot granites as an underground thermal exchanger.

This is because granites are not naturally permeable, so water can only circulate easily in areas where the rock has been fractured by faults. In the Cornish geological context, these faulted zones are vertically shaped, which meant the water had to flow in this direction to gradually extract the heat from the rocks.

Bets are on

Injection and Production wells (Credit: GEL – Youtube)

After raising capital (some of it from the EU before Brexit!) and undertaking studies for over a decade, drilling of the production boreholes took place between 2018 and 2019.  The United Downs project has drilled injection well to a depth of 2,400m and the production well to over 5,000 meters below ground level –  a record for onshore wells in Britain.

More importantly, temperatures of nearly 190 degrees Celsius were recorded at the bottom of the production well, which is sufficient for geothermal power and could only be confirmed once the depth was reached.

The temperature at nearly 5000 meters (Credit: GEL – GEL – Youtube)

Two years later, injection tests took place to see if the water would flow from the injection well and back into the production well. Fortunately, water flow rates between 20 – 60 litres of water per second were observed, which are sufficient for the purpose of driving the foreseen electric turbine.

Adequate water circulation. (Credit: GEL – Youtube)

Additionally, the tests culminated in producing the first geothermal steam in the UK, adding confidence that the project will succeed.

No earthquakes

Geothermal and Fracking tremors are likely. (Credit: GEL – Youtube(4))

Besides not finding the right temperature and reservoir potential after drilling, one of the main concerns with geothermal projects is the potential for earthquakes due to the disturbance in drilling and water pumping in the underlying faulted zone.

This is the same concern as with other on-shore drilling projects like fracking where any injected fluid can act like a ‘fault lubricant’, causing some of these to slip and send seismic waves to the surface.

Fortunately, only two very minor seismic events were registered during drilling and injection tests, which is a positive sign for developing geothermal power in the region. These two tiny earthquakes could only be felt on the surface by seismometers, with their magnitude estimated to be equivalent to a ‘door slamming shut’.

Finding lithium

Lithium is extractable from the geothermal brine (Credit: GEL – Youtube)

Another positive development was encountering world-class lithium concentrations in the water during injection tests. This doesn’t make a difference to the geothermal output whatsoever, but it suddenly opens up lucrative mineral mining as a by-product.

The company secured funding for a demonstration plant that is designed to extract high concentrations of lithium from the water.

Cornwall is known as the premier mining location in Britain due to the presence of these ancient granites.

Granites are solidified remnants of colossal magma chambers that were once filled with metal-rich hot magma that originated deep within the Earth.

Metals like Copper, Gold, Silver and Lithium (among hundreds of others) are further concentrated by groundwater, leaching the metals away from the granite over millions of years and depositing them within ‘hydrothermal veins’.

Precious metals concentrate around granites (Credit: GEL – Youtube)

Cornwall was a favourite area for the Romans, who extracted large amounts of precious metals from its mines.

This continued for the next hundreds of years and reached its peak when Victorian machinery allowed miners to go deeper into mineral-rich formations, which are directly overlapping with these areas now being exploited for geothermal power.

Inevitably, when water from the United Downs system is circulated through these mineral motherloads, some metals like Lithium will leach into the fluid and surface together with the hot water that will drive the turbines.

Lithium is at the core of Li-Ion battery technology and is used to power virtually all of our electronics; smartphones, laptops, tablets, EVs, etc.

The importance of finding these critical resources within the UK can’t be overstated, given that China has secured most of the global lithium resources for its colossal battery industry, and we know how bad monopolies can be.

The future of United Downs

United Downs Geothermal has since signed a Power Purchase Agreement (PPA) with Ecotricity, paving the way for producing the very first commercial geothermal power in the UK.

A binary geothermal power station is currently under construction, in which the geothermal brine is used to heat another fluid to power the turbines. This is due to the geothermal water being too rich in valuable minerals and corrosives that would reduce the turbine’s life.

According to this site, the geothermal power plant will have a capacity of 10 megawatts of electrical power and 55 megawatts of thermal power. This is enough to give electricity for about 10,000 homes and provide heating for many more, although we assume a large proportion of this energy may be used for Lithium extraction.

A geothermal powerhouse?

The whole area has the potential for deep geothermal power (Credit: GEL – Youtube)

United Downs is proving the deep geothermal concept in Cornwall and has given confidence for the continued development in the region.

Planning permission was given in September 2022 for another deep geothermal power station in neighbouring Penhallow, and the company anticipates that it will take three years to complete once ground works can begin.

Yet, there is some resistance from the local community who are concerned about the potential effect on traffic, noise and contamination of drinking water.


The United Downs deep geothermal project is a low-key trailblazer in the UK’s renewable energy market, which may have significant implications in the future.

This is because it proves a novel methodology for extracting deep geothermal energy economically in unorthodox conditions (radioactive rocks!) and is likely to pave the way for the UK to have a more diverse and secure energy portfolio.

And on top of this, the fact that it can also be used for the clean extraction of Lithium is key in decentralising the supply of this key metal from China and helping keep a power balance in the world.

We will keep monitoring any exciting developments and update any of our readers accordingly!

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