A new survey published this morning by the British Geological Survey has confirmed what many have long suspected: the UK sits on a vast reservoir of geothermal energy. The data, compiled over five years using advanced seismic imaging and exploratory drilling, indicates that heat accessible from depths of up to five kilometres could technically supply the nation's entire heating demand for centuries. Yet the same report underlines a persistent roadblock: the upfront costs of drilling and infrastructure remain prohibitively high, with initial outlays for a deep geothermal plant currently exceeding £25 million per megawatt. This tension between abundant resource and economic inertia is now reigniting a crucial conversation about how to price and incentivise a clean energy source that remains, in practice, stubbornly expensive.
Geothermal energy works by exploiting the Earth's internal heat. Water is injected into porous rock, heated by the planet's core at depths of two to five kilometres, and then brought back to the surface to drive turbines or supply district heating networks. In the UK, the granitic batholiths of Cornwall and the deep aquifers beneath the Northeast have long been identified as prime sites. The new survey quantifies these reserves with greater precision: the heat stored in the upper five kilometres of the British crust is equivalent to over 100 times the country's annual primary energy consumption. This is not a theoretical abstraction; it is a physical reality we can measure.
The economic picture is more complex. Deep geothermal wells require custom drilling, often in hard rock, and each site demands its own dedicated power plant or heat network. The average capital expenditure for a 5 MW plant is £125 million, before any revenue is generated. Compare this to solar photovoltaic, where a 5 MW farm can be installed for under £3 million, albeit with lower capacity factors. The levelised cost of geothermal electricity in the UK currently stands at £150 to £200 per megawatt-hour, roughly three times the cost of onshore wind. For heat, the figures are more competitive: district heating networks using geothermal sources can deliver heat at £60 to £80 per megawatt-hour, comparable to natural gas when carbon prices are factored in.
This cost disparity has left geothermal in a policy twilight. While the government has committed £5 billion to heat network grants under the Heat and Buildings Strategy, only a fraction has been allocated to geothermal projects. Pilot schemes in Cornwall and Manchester have demonstrated technical viability, notably the United Downs project in Cornwall which now supplies electricity to over 3,000 homes. But scaling that success to national relevance remains a challenge. The report's lead author, Dr Alistair Thorpe, noted: "The resource is not the issue. It is the financial risk. We are asking private investors to commit sums comparable to small nuclear reactors for a technology they do not fully trust."
Proponents argue that the comparison is unfair. Geothermal, unlike wind or solar, provides baseload power and heat regardless of weather. A 5 MW geothermal plant has a capacity factor of over 90%, outmatching fossil gas combined-cycle turbines. When lifecycle costs are considered, including decommissioning and fuel price volatility, geothermal is competitive. The problem is the discount rate. Investors demand returns in five to ten years, but geothermal projects pay back over 30 to 50 years. This mismatch is structural and will require public intervention.
There are signs of change. The government has announced a new Geothermal Development Fund, seeded with £500 million, to underwrite early-stage exploration drilling. The fund is modelled on the successful Contracts for Difference scheme that catalysed offshore wind. Separately, the Climate Change Committee has recommended that deep geothermal be included in the UK's net zero pathways, noting that without it, decarbonising heating will become heavily reliant on hydrogen or electrification, both of which face their own infrastructure hurdles.
For the public, the appeal of geothermal is visceral. It is domestic, using heat from the ground beneath our homes. It is invisible, emitting no air pollution. And it is resilient, providing energy security independent of foreign gas supplies. The debate now is how fast we can turn that appeal into reality. The data is clear: the heat is there. The cost is the barrier. And the clock on climate targets is ticking.
The next decade will determine whether geothermal remains a footnote in the UK energy story or becomes a central chapter. The technology works. The political will is tentatively emerging. What remains is the most difficult step: aligning the timelines of geology and economics.
