In the quiet Cornish landscape, engineers have drilled deeper than anyone has before to tap the planet’s internal heat. The United Downs Deep Geothermal Power project near Redruth is now generating electricity from superheated water circulating through granite 5 kilometers below the surface. This is not a speculative prototype but a working power plant feeding the National Grid. The technology, called Enhanced Geothermal Systems (EGS), involves fracturing hot, dry rock to create artificial reservoirs for water to circulate. It is the culmination of decades of research and a £24 million investment from the European Union and local authorities.
Geothermal energy has long been a niche player in the renewable energy mix, constrained to regions with shallow volcanic activity like Iceland or New Zealand. The required temperature for efficient electricity generation is above 180°C, and such rocks are usually buried several kilometers deep. Drilling is expensive: a single well can cost up to £15 million. But the UK’s first deep geothermal plant, with a capacity of 3 megawatts, proves that the resource is accessible even in geologically stable areas. The next step will be to scale up and reduce costs.
The potential is staggering. The Earth’s internal heat is essentially inexhaustible on human timescales. According to the International Renewable Energy Agency, the theoretical global resource for geothermal energy exceeds 100,000 exajoules per year, many times the world’s energy consumption. The practical challenge is economic. Current electricity costs from EGS are around £0.15 per kilowatt-hour, about double the cost of onshore wind. But as drilling technology improves and economies of scale kick in, costs are projected to fall to £0.05 per kWh by 2030.
The United Downs project uses directional drilling to reach a fault zone with naturally high temperatures. Water is pumped down at high pressure, heated by the rocks, and brought back to the surface to drive turbines. Unlike solar or wind, geothermal offers baseload power, running 24/7 irrespective of weather. It can also provide heat directly for district heating or industrial processes, which account for nearly half of global energy demand.
The implications for the global energy transition are profound. Countries like Japan, the United States, and Indonesia have vast geothermal resources under their feet. Japan alone has the potential to generate 23 gigawatts of geothermal power, yet currently develops only a fraction of that. The UK breakthrough shows that with the right technology, any country can exploit this resource. It is particularly valuable for decarbonizing industries that require high-temperature heat, such as steel or cement production. Geothermal can also be paired with carbon capture to remove CO2 from the atmosphere through a process called carbon mineralization, where CO2 is injected into the hot rock and converted into solid carbonates.
There are environmental concerns. Induced seismicity, small earthquakes caused by fracturing rock, is a known risk. The United Downs project has been carefully monitored, with only microseismic events recorded. Water usage is another issue, but modern EGS plants circulate water in a closed loop, minimizing consumption. The technology is far safer than fossil fuels, which cause air pollution and climate change.
The UK government has expressed interest in expanding geothermal energy, but funding remains uncertain. The industry needs a long-term support scheme similar to the Contracts for Difference used for offshore wind. Without it, the technology may remain a niche curiosity rather than a mainstream solution.
The heat beneath our feet is abundant and waiting. The United Downs project has proved it is technologically possible. Now it is a matter of economic will. If we take lessons from the rapid cost reductions in solar and wind, geothermal could become a key part of the energy mix within a decade. The Earth’s core is a nuclear reactor, a gift of primordial heat that has been slowly cooling for 4.5 billion years. It is a source of energy that does not depend on the sun or the wind, but on the planet’s own relentless internal engine. We have only begun to scratch the surface.
