Deep geothermal energy, a resource long considered too costly and technically challenging, is being re-evaluated as a potential cornerstone of the UK's future energy mix. With advances in drilling technology and increasing pressure to decarbonise, pilot projects from Cornwall to Scotland are proving that heat from the Earth's core can be tapped at scale.
The principle is simple: drill deep into granite or other hot rocks, circulate water through fractures, and bring the superheated fluid to the surface to drive turbines. Unlike wind or solar, geothermal provides baseload power 24/7, independent of weather. The Cornish project at United Downs, for instance, has reached depths of over 5 kilometres, where rock temperatures exceed 180°C. Initial results show sufficient heat flow to generate electricity for thousands of homes.
Yet the economics remain daunting. Drilling costs for a single deep well can exceed £20 million, and the risk of hitting insufficient permeability or dry zones is real. The levelised cost of electricity from deep geothermal is currently around £150 per megawatt-hour, roughly triple the cost of offshore wind. Subsidies or carbon pricing mechanisms would be needed to make it competitive.
Proponents argue that these costs will fall as technology matures. The oil and gas industry's experience with horizontal drilling and hydraulic fracturing can be adapted for geothermal. The UK Continental Shelf also provides a skilled workforce and supply chain. Moreover, geothermal plants occupy a small surface footprint and have low visual impact, a distinct advantage in a densely populated country.
Critics point to historical failures, such as the abandoned project at Southampton, and the risk of induced seismicity. However, modern monitoring techniques can mitigate seismic hazards. The real bottleneck is upfront capital. Without sustained government support, private investment will remain cautious.
The potential prize is enormous. The British Geological Survey estimates that deep geothermal could meet up to 20% of the UK's electricity demand if widely deployed. It would also provide a source of heat for district heating networks, which is where the technology becomes transformative. Unlike electricity, heat constitutes half of the UK's energy consumption, and most of it comes from natural gas. Geothermal heat could decarbonise this sector directly.
There is a sense of calm urgency around these developments. The climate does not wait for economic hurdles to be cleared. While solar and wind are scaling rapidly, they cannot alone replace fossil fuels without massive storage or backup. Geothermal offers a reliable complement, a steady hum beneath the intermittent chorus of renewables.
The government's recent allocation of £31 million for deep geothermal projects in the Net Zero Innovation Portfolio is a start, but industry leaders stress that more is needed. A stable price guarantee for geothermal electricity, akin to Contracts for Difference for offshore wind, could unlock investment. If the UK can mobilise its geological and engineering heritage, the ground beneath us may indeed become a foundation for a resilient, low-carbon grid.
