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The resource

The deep geothermal resource in Cornwall represents a significant opportunity for renewable heat and power generation. In the 1970’s and 80’s the world renowned ‘Hot dry rocks project’ at Rosemanowes Quarry in Penryn, led  by Camborne School of Mines, confirmed the high temperatures which are found deep underground in Cornwall’s granite. A recent study suggests this resource could meet all of Cornwall’s demand for electricity and 20% of the UK’s demand. Cornwall could lead the way in this new energy sector.

Heat Flow Map

Deep geothermal heatflow map


The benefits

If accessed and exploited appropriately, this estimated level of resource could provide Cornwall with significant economic and social benefits. Geothermal electricity offers advantages over other renewable energy sources; it provides baseload generation (24/7, 365 days of the year), as well as being able to react quickly to changes in demand, contributing longer term to a smarter energy system. In addition to generating power, the secondary heat produced by the process can also be used.  This could form part of a longer term plan to tackle fuel poverty, support and attract businesses with high heat demand and safeguard existing jobs. Geothermal also has a very small footprint on the landscape when compared to the same generating output of other technologies and emits no greenhouse gases.

The barriers

Cornwall Council has, where possible, sought to reduce the barriers facing the industry, such as licensing and protecting the resource, access rights to drill, concerns around earth tremors and ongoing subsidy support, through close partnership working with the Department of Business, Energy and Industrial Strategy and through the development of geothermal Supplementary Planning Guidance.

Up to this point uncertainties about the geological and geothermal conditions (the ‘ground risk’), alongside high upfront capital costs have put off private sector investment.

Having been identified as a priority investment area in the Cornwall and Isles of Scilly growth programme a project has now been successful in securing funding through European Regional Development Fund (ERDF) and work is underway. The £18m United Downs Deep Geothermal Power project at United Downs near Redruth, led by Geothermal Engineering Limited (GEL), has secured £10.6m ERDF, match funded by £2.4m from Cornwall Council and £5m from the private sector. 

The technology

EGS technology for the geology of cornwall image. The type of technology used to extract geothermal energy (heat from deep underground), is dependent on the site geology; the underground rock type, and the temperature underground. The geothermal resource has been used  for thousands of years for bathing and space heating using natural springs. Power generating plants have traditionally been sited on the edge of tectonic plates, where very high temperatures can be accessed near to the surface. Iceland has many examples of this type of technology.

Conventional geothermal power generation requires a natural source of circulating water at depth and at a high temperature. The geology in Cornwall is granite; this lacks natural circulating water, but has the high temperatures.

The technology proposed in Cornwall appropriate for the granite is known as engineered or enhanced geothermal systems (EGS). It is also sometimes referred to as ‘hot dry rocks’. With EGS technology it is possible to increase the ability for water to circulate between wells, at depths of 4-5km, to capture the natural heat source within the rock. The extracted hot water is at a sufficiently high temperature to drive an electricity generating turbine. EGS is a relatively innovative technology but there are generating projects in Europe, the US, and Australia, with many more in the pipeline.

The United Downs Deep Geothermal Power project will be testing a different system where two wells will be drilled, one 2.5km deep and the other 4.5km deep. 

Many issues will be assessed as part of the planning permission process. The Council has developed clear Supplementary Planning Guidance for all renewable energy technologies that include a specific section on geothermal.