Beneath our feet lies a colossal reservoir of energy, largely untapped in Britain: geothermal heat. The granitic rocks of Cornwall and the deep aquifers under other regions reach temperatures in excess of 200 degrees Celsius, offering a steady, carbon-free baseload power source that could supply more than 20% of the nation's electricity by 2050, according to recent estimates from the British Geological Survey. Yet for decades, the high cost of drilling, coupled with geological risk, has kept this potential in the ground.
That is now changing. A new wave of British geothermal pioneers, including Geothermal Engineering Ltd and Cornish Lithium, are deploying advanced drilling techniques borrowed from the oil and gas industry, such as horizontal drilling and hydraulic stimulation, to make the economics work. The company is targeting the 'hot dry rock' resource beneath Cornwall, where granite acts as a natural radioactive heat source. Their latest project, a 5 MW demonstration plant near Redruth, is expected to come online in 2025, with costs having fallen by 40% compared to previous attempts a decade ago.
Geothermal's advantage is its dispatchability. Unlike wind and solar, which fluctuate with weather, geothermal plants can run at capacity factors of 90% or more, providing firm power to complement intermittent renewables. This is critical for grid stability as the UK progresses toward net zero. The technology is well established in other volcanic regions, including Iceland, New Zealand, and parts of the United States. In Britain, the challenge is that the heat resource is deeper, typically 3 to 5 kilometres, and requires fracturing of crystalline rock to create permeability.
Drilling accounts for 40-60% of total project cost, and a single well can cost between £5 million and £10 million. This is where innovation is accelerating. The pioneers are adopting 'plug and perf' techniques, multistage fracturing, and using improved casing materials to survive the corrosive brines encountered deep underground. There is also growing interest in 'closed-loop' systems that circulate a working fluid through a sealed pipe, avoiding the need for fluid extraction and reducing induced seismicity risk.
The government has taken notice. The UK's Net Zero Innovation Portfolio has allocated £20 million to a 'Geothermal Deep Heat' competition, supporting studies and pilot projects. Industry body the Geothermal Association now counts over 30 active members, including major engineering firms like Arup and Atkins. However, subsidies remain absent from the Contracts for Difference scheme, forcing developers to compete with cheap wind and gas.
Critics point to the geological uncertainty: each site is unique, and results from early wells in Cornwall have been mixed. The Eden Project geothermal plant, one of the most publicly known, has faced repeated delays and cost overruns, demonstrating the real-world difficulties. Yet proponents argue that learning by doing is essential, and that the potential reward is worth the risk.
If the current pilots succeed, the implications extend beyond electricity. Geothermal heat can be used directly for district heating, displacing gas boilers in homes and businesses. In cities built on shallow aquifers, such as Southampton, such systems have operated for decades. Deeper, hotter resources could also provide process heat for industry, or even produce hydrogen through high-temperature electrolysis.
Geothermal energy is not a silver bullet. It cannot be deployed everywhere and its development is slower than solar or wind. But as a consistent, resilient baseload source, it offers a vital piece of the energy puzzle. The question is whether the current pioneers can prove the economics at scale. If they do, the energy beneath our feet may finally begin to flow.
