Geothermal energy is not a distant future technology; it is already generating power and heating buildings across the UK. Unlike wind and solar, which depend on the weather, geothermal energy provides a steady, baseload supply of heat and electricity because the Earth’s interior continues to produce heat naturally. This makes it a critical part of the puzzle for decarbonising both the grid and the heating sector.
The UK has long relied on imported gas for its energy needs. Tapping into the heat stored beneath our own ground offers a way to generate power locally, create jobs in regions like Cornwall and Northern England, and reduce carbon emissions. While the technology is mature in volcanic regions like Iceland, bringing it to the UK requires drilling deeper and using specific techniques. This guide explains exactly how the technology works, what the current costs are, and where the UK’s geothermal projects stand today.
How geothermal energy works
The Earth’s interior heat comes from two sources. One is the slow radioactive decay of uranium, thorium and potassium in rocks, a process that happens naturally in all rocks. The other is primordial heat left over from the planet’s formation. This heat flows continuously from the hot interior towards the cooler surface. In the UK, the average geothermal gradient is 26 °C per kilometre of depth, though it can exceed 35 °C/km in specific areas.
There are several ways we can tap into this heat, depending on how deep we drill and what temperature we reach.
Geothermal power plants and electricity generation
To generate electricity, we generally need temperatures above 150 °C. There are three main types of geothermal power plant:
- Dry steam: Steam from the reservoir drives the turbine directly. This is the simplest technology but requires very high-temperature resources.
- Flash plants: High-pressure hot water is depressurised, causing it to “flash” into steam. This steam then drives a turbine.
- Binary (Organic Rankine Cycle, ORC): This is the technology used at the United Downs plant in Cornwall. Moderately hot geothermal water passes through a heat exchanger to heat a secondary fluid with a lower boiling point. That secondary fluid vaporises and drives the turbine. The geothermal fluid stays in a closed loop, which means it is not released into the atmosphere.
Enhanced geothermal systems (EGS)
Often called “hot dry rock” or petrothermal systems, EGS is designed for areas where the rock is hot but not permeable enough for water to circulate naturally. By injecting fluid at high pressure, engineers create or widen fractures in the rock. This creates a circulation path between wells, allowing water to absorb heat and return to the surface. The UK ran a “hot dry rock programme” from 1977 to 1994, including experiments in Cornish granite. Our history of geothermal energy development covers the background.
Minewater heat and shallow heat pumps
Not all geothermal energy involves drilling miles underground. About 25% of UK homes and businesses sit above former coal mines, according to the government. The water in these flooded mines is warmed by the geothermal gradient, typically sitting at 10–20 °C, though it can reach 40 °C at around 1 km depth. By using heat pumps to upgrade this temperature, we can provide heating to homes. This is known as minewater heat.
Similarly, shallow ground-source heat pumps (GSHPs) use the near-surface ground (from a few metres to under 200 m) as a heat source. At 10–15 metres deep, the ground temperature roughly equals the mean annual air temperature. While these systems are highly efficient, they are technically tapping into stored solar and atmospheric heat rather than the deep Earth’s heat. The DESNZ/Arup review classifies these as shallow geothermal, distinct from deep systems.
The global picture
Geothermal energy is a major player in the global renewable energy mix. According to the IEA, geothermal meets about 1% of global electricity demand. However, its share is much higher in specific countries.
Installed capacity and leading countries
There are two main sources for global capacity figures, and they differ slightly due to how they count capacity. IRENA, which counts maximum net capacity, reported that the world had 15,624 MW of geothermal power capacity at the end of 2025. ThinkGeoEnergy, using its own industry database, places the global capacity at 17,173 MW.
The top countries vary depending on which dataset you use:
| Rank | Country (IRENA) | MW (IRENA) | Rank | Country (ThinkGeoEnergy) | MW (ThinkGeoEnergy) |
|---|---|---|---|---|---|
| 1 | Indonesia | 2,744 | 1 | USA | 3,953 |
| 2 | USA | 2,696 | 2 | Indonesia | 2,742 |
| 3 | Philippines | 2,057 | 3 | Philippines | 2,034 |
| 4 | Türkiye | 1,758 | 4 | Türkiye | 1,797 |
| 5 | New Zealand | 1,283 | 5 | New Zealand | 1,259 |
| 6 | Mexico | 999 | 6 | Kenya | 980 |
| 7 | Kenya | 925 | 7 | Mexico | 976 |
| 8 | Iceland | 788 | 8 | Italy | 916 |
| 9 | Italy | 772 | 9 | Iceland | 808 |
| 10 | Japan | 469 | 10 | Japan | 607 |
Germany has 78 MW. The main discrepancy lies with the USA: ThinkGeoEnergy lists 3,953 MW, while IRENA lists 2,696 MW. This difference alone shifts the number one spot between Indonesia and the USA.
Iceland’s success
Iceland is the world leader in utilising geothermal heat. According to Samorka, the Icelandic energy and utilities association, 90% of housing in Iceland is heated directly with geothermal energy. On a national scale, geothermal supplied 62% of Iceland’s primary energy in 2018. In 2019 it had 755 MWe of geothermal power across nine plants; IRENA puts its capacity at 788 MW at the end of 2025.
The future of geothermal energy
The IEA’s “The Future of Geothermal Energy” report (December 2024) outlines an ambitious scenario. If project costs continue to fall, geothermal could meet 15% of global electricity demand growth to 2050. This would require up to 800 GW of capacity worldwide, producing annual output equal to the combined electricity demand of the USA and India today.
Next-generation geothermal costs could fall by 80% by 2035, reaching about US$50/MWh. The sector could grow sixfold to create 1 million jobs by 2030. However, the report notes that while over 100 countries have policies for solar and wind, only 30 have specific geothermal policies. These are scenario estimates, not forecasts.
The first commercial next-generation projects are now running. In the US, Fervo Energy’s Cape Station in Utah, an enhanced geothermal system, declared commercial operation of its first 33 MW unit on 30 September 2026. The company calls it the first greenfield EGS development in the world to reach that point.
Geothermal energy in the UK
The UK lacks the tectonic setting for high-temperature hydrothermal power, but it has significant low- to moderate-temperature resources. There are four main areas with granites suitable for Enhanced Geothermal Systems (EGS): south-west England, northern England, the eastern Highlands of Scotland, and the Mourne Mountains of Northern Ireland.
United Downs: the UK’s first deep geothermal power plant
The United Downs project, operated by Geothermal Engineering Ltd (GEL) near Redruth in Cornwall, marked a major milestone. It started generating in February 2026, becoming the UK’s first deep geothermal power plant. Octopus Energy buys its output under a power purchase agreement. Our 2024 report on the UK’s first geothermal power plant in Cornwall covers the run-up.
The plant uses a binary ORC system. It has a gross capacity of 3 MWe, though it secured a Contracts for Difference (CfD) for 2 MW. The production well is 5,275 metres in measured depth (5,057 metres true vertical), making it the deepest well ever drilled in the UK. The water temperature is over 180 °C. The plant uses an air-cooled condenser, meaning it needs no cooling water and releases no vapour plume.
The brine also contains over 340 ppm lithium carbonate equivalent. Production of lithium started in February 2026 with a capacity of 100 tonnes per year. GEL aims to scale this to over 18,000 tonnes per year within a decade; the company says that would be enough for about 250,000 electric car batteries a year.
GEL has two additional sites in Cornwall, Manhay and Penhallow, which are expected to add 10 MW of baseload power by 2030.
Geothermal heat in Cornwall and beyond
Beyond electricity, the UK is using geothermal heat for buildings. The Eden Project in St Austell began generating heat in June 2023. A single well drilled 4,871 metres vertically supplies heat at 85 °C to the Biomes and other buildings. It is estimated to save up to 500 tonnes of CO2 per year.
In 2023 the Green Heat Network Fund awarded £22 million to a planned heat network for about 3,800 homes at Langarth Garden Village near Truro, designed to use heat from the United Downs well.
Minewater heat schemes
The UK has a legacy of coal mining, and abandoned mines are now a source of clean heat.
- Gateshead: Full operation began in March 2023. It uses heat pumps to extract heat from mine water 150 metres below the town centre. It heats 350 high-rise homes and several public buildings.
- Seaham Garden Village: Operations started supplying heat to about 750 homes. The scheme extracts heat from the Dawdon mine water treatment scheme.
- Lindsay, Wales: Another operating mine water heat scheme listed by the government.
Other UK projects and policy
The Southampton District Energy Scheme is the only tangible legacy of the 1970s–80s UK Geothermal Energy Programme. Its single well produced water at about 75 °C for the city’s heat network, but it was reported closed for repairs in June 2023.
In Northern Ireland, the GeoEnergy NI demonstrator project has completed its first phase: boreholes were drilled at Stormont, and a planning application for a deep geothermal system at Greenmount near Antrim was approved. The Mourne Mountains granites need further investigation before they can be called suitable for EGS. Earlier coverage: hidden geothermal energy beneath Antrim.
In Stoke-on-Trent, the city’s district heat network was planned around a deep geothermal source; the council said in January 2024 that it should become available around 2028. See our earlier report on Stoke-on-Trent’s geothermal scheme.
The UK government awarded its first ever geothermal Contracts for Difference (CfDs) in Allocation Round 5 (September 2023). Three GEL projects were awarded a total of 12 MW at a strike price of £119/MWh (in 2012 prices): United Downs (2 MW), Manhay (5 MW) and Penhallow (5 MW).
Advantages and disadvantages of geothermal energy
Geothermal energy has distinct benefits, but it is not without its drawbacks.
| Advantages | Disadvantages |
|---|---|
| Baseload power: The average global capacity factor was 88% in 2024. Output does not depend on the weather. | High upfront costs: Drilling is expensive. UK deep geothermal electricity costs range from £60/MWh (mature) to £609/MWh (first-of-a-kind). |
| Small land footprint: The US Department of Energy puts geothermal at about 404 m² per GWh, against 1,335 m² for wind and 3,237 m² for solar PV. | Location dependent: High-temperature resources are concentrated in specific geological areas, like the Cornish granites. |
| Low emissions: Closed-loop binary plants like United Downs avoid most emissions. | Induced seismicity: Fluid injection can trigger small earthquakes. The Pohang plant in South Korea was shut down after a magnitude 5.4 quake. |
| Co-products: Lithium can be extracted from the brine, adding revenue streams. | Long lead times: UK deep projects take about 6–8 years from planning to commissioning; the IEA says up to a decade worldwide. |
| Heat networks: Deep geothermal can provide high-temperature heat for district heating. | Heat transport limits: Hot water cannot be piped economically over very long distances. |
Costs and outlook for the future
The cost of geothermal energy varies wildly depending on whether it is a first-of-a-kind project or a mature technology. According to the DESNZ/Arup review, UK deep geothermal electricity for Cornish granites at 4–5 km depth ranges from £609/MWh (first-of-a-kind, high scenario) down to £60/MWh (mature technology, low scenario by 2050). The central estimate for a first-of-a-kind plant with heat revenue is £169/MWh.
Globally, the weighted-average levelised cost of energy (LCOE) for newly commissioned geothermal power was US$0.060/kWh in 2024. This is higher than onshore wind (US$0.034/kWh) and solar PV (US$0.043/kWh), but competitive with offshore wind (US$0.079/kWh).
The future of geothermal energy looks promising if drilling costs can be reduced. The IEA estimates that next-generation geothermal costs could fall by 80% by 2035. According to the IEA, up to 80% of the investment needed involves capacity and skills transferable from the oil and gas industry, which matters for a country with a large North Sea workforce.
Frequently asked questions
Is geothermal energy renewable?
Yes. The US EIA classifies geothermal as renewable because the Earth constantly produces heat through radioactive decay and primordial heat. However, individual reservoirs can be depleted if heat or fluid is extracted faster than it is replenished. Sustainable use relies on reinjecting fluid and careful monitoring.
Does the UK use geothermal energy?
Yes, though on a small scale compared to other renewables. The UK has one operating deep geothermal power plant, United Downs in Cornwall, and a deep geothermal heat well at the Eden Project. Minewater heat schemes run in Gateshead, Seaham and Lindsay in Wales.
Where is the UK’s first geothermal power plant, and how much electricity does it make?
The UK’s first deep geothermal power plant is United Downs, located near Redruth in Cornwall. It has a gross capacity of 3 MWe and began generating power in February 2026. It also produces lithium as a co-product.
Is a ground-source heat pump the same as geothermal energy?
Not quite. Both draw heat from the ground, but they work at very different depths and temperatures. Shallow ground-source heat pumps (GSHPs) use the near-surface ground (usually under 200 metres) as a heat source. The temperature there is stable but low, roughly equal to the mean annual air temperature. Their heat is mostly stored solar and atmospheric heat, and a heat pump has to raise it to a useful temperature. Deep geothermal taps the Earth’s internal heat at much higher temperatures. The government’s 2025 geothermal review classes shallow systems as under 500 metres deep.
Can geothermal energy cause earthquakes?
Yes, this is known as induced seismicity. Injecting fluid into rock can trigger small earthquakes. At United Downs, 171 small earthquakes, from magnitude −1.3 to 1.7, were recorded between August 2020 and January 2021 after flow testing began; only two exceeded magnitude 1.5. In Pohang, South Korea, a magnitude 5.4 earthquake in 2017 was linked to an EGS plant, leading to its permanent closure.
How hot does it get underground in the UK?
The UK average geothermal gradient is 26 °C per kilometre of depth. In the Cornish granites, the gradient is higher, at 33–35 °C/km. At 7 km depth in Cornwall, temperatures can reach 210–330 °C. Outside the granites, temperatures at 7 km rarely exceed 140 °C.
Which country uses the most geothermal energy?
According to IRENA, Indonesia has the highest installed capacity (2,744 MW), followed by the USA (2,696 MW). According to ThinkGeoEnergy, the USA leads with 3,953 MW. Iceland uses the highest proportion of geothermal energy relative to its total energy consumption, with 62% of its primary energy coming from geothermal sources.
Is geothermal energy expensive compared with wind and solar?
In 2024, the global weighted-average LCOE for geothermal was US$0.060/kWh. This is more expensive than onshore wind (US$0.034/kWh) and solar PV (US$0.043/kWh). However, geothermal offers baseload power with an 88% capacity factor, whereas wind and solar are intermittent.