A quiet revolution is underway beneath our feet. Geothermal energy, long dismissed as a niche player confined to volcanic regions, is poised for a global breakout. And UK companies are at the forefront, drilling deeper than ever to unlock a near-limitless source of clean, baseload power.
This is not the shallow geothermal of ground-source heat pumps. This is deep geothermal: tapping into the Earth’s crust at depths of 4 to 10 kilometres, where temperatures exceed 200°C. Here, superheated water or steam can drive turbines 24/7, independent of weather or daylight. The resource is enormous. According to the International Energy Agency, deep geothermal could supply 10-15% of global electricity by 2050 with the right investment. Today, it accounts for less than 1%.
What has changed? Drilling technology. Advances in directional drilling, borehole lining, and reservoir stimulation — techniques borrowed from oil and gas — have slashed costs. Whereas a 5 km well in 2010 cost $30 million, today it can be done for under $15 million. And several UK firms are pushing the envelope.
At the heart of the action is Geothermal Engineering Ltd, based in Cornwall, which is developing the United Downs Deep Geothermal Power project. Two wells have already been drilled to depths of 5.1 kilometres, targeting hot granite rocks. The project aims to generate 3 MWe of electricity, enough to power 6,000 homes. Even more ambitious is the Eden Geothermal project, adjacent to the Eden Project, which plans to drill to 4.5 km for both heat and power.
Meanwhile, startup Magma Energy is exploring superhot rock geothermal. The concept: drill deep enough to reach rocks at 400°C, where water becomes ‘supercritical’ — a fluid with properties of both liquid and gas that can carry vastly more energy. Tests in Iceland and Italy suggest a single supercritical well could produce ten times the power of a conventional geothermal well. Magma has secured £12 million in seed funding to drill a 7 km well in Cornwall, targeting depths no UK borehole has reached before.
Why Cornwall? The region sits on a large granitic batholith, rich in radiogenic heat from decaying uranium and thorium. The geothermal gradient here is about 60°C per kilometre, higher than the global average. That makes it a natural laboratory, but the technology is transferable. Similar hot rock formations exist in Western Australia, East Africa, and parts of the United States.
The economics are compelling. Levelised cost of electricity (LCOE) for deep geothermal is now around $80 per MWh, competitive with offshore wind and solar-plus-storage. And because it runs constantly, it avoids the integration costs of intermittent renewables. For a grid scrambling to decarbonise, that is invaluable.
But challenges remain. Drilling risks are high. Fracturing the rock to create permeability can induce seismicity, though typically at magnitudes below human detection. There is also the issue of water use, but advanced closed-loop systems can minimise consumption. And upfront capital is still substantial: a 50 MWe plant might cost $250 million.
Nevertheless, the trajectory is clear. The UK government has recognised this, announcing a £32 million Deep Geothermal Challenge Fund in 2022. The European Union has included geothermal in its Net-Zero Industry Act. And global investment in geothermal reached $5.6 billion in 2023, up 30% year-on-year.
What we are witnessing is not just an energy transition. It is a geological transition. For billions of years, the Earth’s internal heat has been dissipated slowly and silently. Now, with cunning and steel, we are learning to tap it. The future of cheap, clean power may well be the heat beneath our feet.
