The bedrock beneath the British Isles is stirring a quiet revolution. Geothermal energy, the heat trapped within the Earth’s crust, is being touted as a reliable, low-carbon power source for the UK. But it is not cheap, and proponents are now clamouring for government investment to prove its viability.
Geothermal energy works by tapping into hot rocks deep underground, often at depths exceeding five kilometres, where temperatures can reach 150 to 200 degrees Celsius. Water is circulated through fractures in these rocks, heated, and then brought to the surface to drive turbines. Unlike wind or solar, geothermal is baseload power: it runs 24/7, unswayed by weather or time of day. For a grid increasingly reliant on intermittent renewables, this constancy is invaluable.
The UK sits on abundant geothermal resources. The granites of Cornwall, the sedimentary basins of the North East, and the hot aquifers beneath London all hold significant heat. Estimates suggest geothermal could supply up to 20 per cent of the UK’s electricity needs, and far more for heating. Yet despite these numbers, the industry remains nascent. Only one commercial geothermal power plant operates in the UK, the United Downs Deep Geothermal Power project in Cornwall, which began generating in 2024.
The principal barrier is cost. Drilling a single geothermal well can cost £10-20 million, with no guarantee of success. Exploration risk remains high: not every borehole will find sufficient heat or water flow. This upfront cost deters private investment without government guarantees. By contrast, offshore wind has seen costs plummet due to decades of subsidies and supportive policy.
Geothermal firms are now pushing for a Contract for Difference (CfD) scheme similar to that which boosted offshore wind. CfDs guarantee a fixed price for electricity generated, protecting developers from low wholesale prices while ensuring affordable returns. The industry argues that a small initial investment could unlock a vast, domestically sourced energy supply, free from import dependencies and price volatility.
The case for geothermal extends beyond electricity. Heat networks, which distribute hot water from geothermal sources to homes and businesses, could decarbonise a sector that accounts for nearly half of UK energy consumption. Geothermal heat is already used in district heating schemes in Iceland, France, and Germany. For the UK, with its aging gas boilers, a switch to geothermal heat could significantly reduce emissions.
Environmental concerns are minimal. Geothermal plants have a small land footprint, produce no combustion emissions, and can operate for decades with minimal maintenance. On the downside, there is a risk of induced seismicity, small earthquakes caused by fluid injection. However, these events are typically too small to be felt, and modern engineering techniques mitigate the risk.
The clock is ticking. The UK has committed to net-zero emissions by 2050, and progress in decarbonising heat and electricity is lagging. While wind and solar will do the heavy lifting, geothermal offers a steady, dispatchable complement. But without policy support, the inert heat below may remain untouched.
As Dr. Helena Vance might say: The planet is warming and we have cheap solar and wind. We don't need expensive options. But if we want reliable, always-on clean power, geothermal could be the deep, quiet answer. The science is clear; the economics remain the question.
