The Earth beneath our feet is a nuclear reactor. That is the blunt physical reality. The heat generated by radioactive decay in the planet’s core and mantle is a constant, zero-carbon energy source. For decades, its exploitation has been limited to volcanic hotspots like Iceland or shallow aquifers in parts of the UK. That is changing. The UK Infrastructure Bank today announced a strategic review of deep geothermal projects, signalling that the next wave of low-carbon heat and power may come from drilling several kilometres into granite rock.
Granite. It is the rock type that contains high concentrations of uranium, thorium, and potassium. As these isotopes decay, they produce heat. At depths of 4 to 6 kilometres, temperatures in Cornish granite can exceed 180 degrees Celsius. That is hot enough to drive supercritical steam turbines. The Infrastructure Bank’s move is not merely a funding signal. It is a recognition of a fundamental shift: enhanced geothermal systems (EGS) have moved from laboratory curiosity to commercial reality.
The physics of EGS is elegant. You drill a deep well, fracture the hot rock by injecting high-pressure water, and create a subsurface heat exchanger. Water circulates, absorbs heat, returns to the surface, and drives turbines. Unlike wind or solar, it is baseload power. It operates 24/7. The UK has vast quantities of granite. The Cornwall Geothermal District heating project already uses warm water from 5 km depth to heat 400 homes in United Downs. But the scale now under consideration is industrial.
The Infrastructure Bank’s interest comes at a time when the UK’s energy trilemma is acute: secure supply, affordable prices, and net-zero emissions. Geothermal ticks all three. Levelised cost of electricity from EGS is projected to fall below 6 pence per kWh for new projects by 2030, competitive with offshore wind. Yet the UK has barely scratched the surface. A report by the British Geological Survey estimates that geothermal energy could meet 10% of the UK’s electricity demand and 90% of its heating demand. The infrastructure needed is smaller than that of a gas grid.
But nuances exist. Drilling is expensive. A single well can cost £5 million to £10 million. And the risk of induced seismicity, though low, requires careful regulatory oversight. The Infrastructure Bank will likely provide loans or guarantees to de-risk early projects. The model is inspired by the Global Geothermal Alliance’s success in Indonesia and Kenya.
The human response to this news should be quiet enthusiasm. This is not a silver bullet. It is a solid data point. The energy transition will be a mosaic of technologies: solar, wind, nuclear and geothermal. For too long, the UK has ignored the heat beneath its laboratories. That is a mistake. The Earth’s crust is a resource. We are now learning to tap it.
Let us be clear: the clock is ticking. Biosphere collapse does not pause for drilling schedules. But every gigawatt of geothermal power is a gigawatt of coal not burned. The calm urgency of this moment demands that we use every tool. The infrastructure fund’s announcement is a step. The next step is drilling. And then many more drills.
