Engineers at Rosemanowes Quarry in Cornwall have extracted geothermal heat from a borehole using a system they say could be used to supply heat to thousands of buildings across the UK.
Geothermal Engineering has been developing its “single-well” technology, also known as the “standing column well”, for the last two years and has been trialling the technology at the Rosemanowes site for the last two months.
Deep geothermal plants normally use multiple boreholes drilled several kilometres deep. Cold water is pumped down to hot granite rocks. This heats the water to temperatures of around 200ºC. The water is pumped back to the surface via a different borehole, where it can then be used to drive turbines to generate electricity.
Geothermal Engineering's system only extracts water at temperatures between 55 and 60ºC, hot enough for use in domestic heating systems, but unsuitable for electricity generation. However, it works at much shallower depths, between 1.5 and 2km, and only requires a single well for extraction and reinjection. It is therefore cheaper and easier to set up than larger, deeper geothermal systems that produce electricity.
Ryan Law, managing director of Geothermal Engineering, said: “There has been a lot of discussion and talk about deep geothermal over the last six years, but no one has delivered because of the lack of available finance and regulatory problems.
“This is on a much smaller scale and you're drilling less. The reduced temperature also opens up many more potential sites, throughout the South, South West and North East.
The system produces enough heat to supply an apartment block of around 400 flats, or other large buildings such as schools or offices, and could be installed next to such buildings, said Law. The well is “recharged” during warmer months by pouring cooler water down it, which slowly soaks through the rock strata to be warmed prior to extraction. This input and output has to be balanced. Law said: “The tests at Rosemanowes have assessed how the well performs as we take the energy out and put the water in.
“The project shows that we can deliver deep geothermal energy in Cornwall and we look forward to developing further projects in the region.”
The company is looking to develop commercial projects with partners looking to supply renewable, deep geothermal heat to buildings and plans to announce “a number of high profile projects” during the next 12 months.
Geothermal Engineering announced in 2009 it was planning to build a plant at Rosemanowes capable of generating 10MW of electricity and 55MW of heat, which would be expandable to 300MW of electricity and 1GW of heat. The company initially received a £1.5 million government grant, but had a further £6 million grant withdrawn for the larger plant in 2013 because it could not find private financial backing for the project. The single-well system was developed using a £800,000 government grant awarded last year.
Energy secretary Ed Davey, said: “We need a broad base of renewable energy in the UK and I am pleased to see that a deep geothermal heat project is finally producing energy.”
The commissioning of the single-well system marks the first time geothermal heat has been extracted in Cornwall since the 1970s, when Rosemanowes hosted a series of so-called “hot-rock” experiments. The results of the experiments influenced the development of a limited number of geothermal plants around the world.