The Construction Behind the UK’s First Geothermal Plant

After nearly two decades of development and US$63m in expenditure, the UK's first deep geothermal power plant was switched on in Cornwall.

This marks a small but symbolically significant moment for the country's renewable energy mix.

The United Downs plant, operated by Geothermal Engineering Ltd (GEL) near Redruth, has been almost 20 years in the making.

Ryan Law, CEO of GEL, is candid about the journey to get here: "To finally reach this point is exciting – and a bit of a relief."

The plant works by circulating water through fractures in granite rock some 5km below the surface, where temperatures reach close to 200C.

Drilling into granite rock

These geological conditions are not that common in the UK. In most of the country it is generally the case that drilling down a kilometre leads to a 20C rise in temperatures.

However, the granite on which Cornwall rests is better at retaining heat. This means that temperatures rise by about 40C for every kilometre drilled.

Once the hole has been bored, superheated water from its lowest point is pumped to the surface.

Here steam drives a turbine before the cooled water – now at around 50C – is re-injected into the fault line to be reheated, completing the cycle.

The electricity generated has been sold to Octopus Energy which will supply it via the National Grid to meet the needs of up to 10,000 homes.

Unlike wind and solar, geothermal generation is continuous. This is an attribute that Ryan stresses is central to its value proposition.

Continuous renewable energy supply

"Unlike other renewable sources like wind and solar we are constantly on, 24/7 electricity," he says.

Ryan adds that the absence of fuel costs means there are no price fluctuations of the kind seen with gas.

Global investment in deep geothermal electricity has grown 80% year-on-year since 2018.

This is driven in part by the energy demands of data centres operated by the likes of Google, Meta and Microsoft.

It is a market dynamic that industry body Geothermal UK believes should sharpen the government's focus.

Anne Murrell, who is Head of Geothermal UK, argues that the sector remains under-supported at a policy level.

"The challenges we have include investment, and to unlock investment and increase investor confidence, we need a supportive government policy framework," she explains.

"Geothermal needs to be recognised by government as a key part of our energy strategy."

Lithium extraction and future outlook

Perhaps as significant as the electricity output is the plant's secondary function which is lithium extraction.

The mineral-rich water drawn from the Porthtowan Fault Zone contains lithium carbonate. This is a critical material in the production of rechargeable batteries.

Initially the site will produce around 100 tonnes of lithium annually which is enough for 1,400 electric vehicles.

GEL says it plans to scale this to 18,000 tonnes per year within a decade which could supply roughly 250,000 EVs annually.

The UK government contributed US$2.27m covering half the cost of the initial lithium extraction facility.

China currently processes more than 60% of the world's lithium. Domestic production at any meaningful scale would represent a notable shift in supply chain exposure for British battery manufacturers.

The British Geological Survey (BGS) described the plant as a "major step forward" for geothermal but has also noted that high drilling costs make replication difficult.

Deep geothermal is also technically feasible in Scotland and the north-east of England though there are currently no approved plans for either region.

GEL has two further Cornwall sites in development. One has been initially refused planning permission on environmental grounds which is a decision the company is appealing.

The US$63m spent so far was funded through private investors and US$18.9m from the European Development Fund.

This is a source of financing that is no longer available to UK projects following Brexit.

Whether the government's recent appointment of Lord Whitehead as the country's first geothermal minister translates into the kind of policy framework the industry is seeking remains to be seen.

China currently processes more than 60% of the world's lithium. Domestic production at any meaningful scale would represent a notable shift in supply chain exposure for British battery manufacturers.

The British Geological Survey (BGS) described the plant as a "major step forward" for geothermal but has also noted that high drilling costs make replication difficult.

Deep geothermal is also technically feasible in Scotland and the north-east of England though there are currently no approved plans for either region.

GEL has two further Cornwall sites in development. One has been initially refused planning permission on environmental grounds which is a decision the company is appealing.

The US$63m spent so far was funded through private investors and US$18.9m from the European Development Fund.

This is a source of financing that is no longer available to UK projects following Brexit.

Whether the government's recent appointment of Lord Whitehead as the country's first geothermal minister translates into the kind of policy framework the industry is seeking remains to be seen.