The geothermal resource of the radiothermal granites of the UK

• Engineered geothermal systems (EGS), also termed ‘hot dry rock’ or ‘petrothermal’ systems, make use of crystalline basement rocks such as granite. Granites have enhanced heat flows due to enrichment of the radioactive elements uranium, thorium and potassium, making them particularly suitable as a geothermal resource.
• To be most suitable for EGS, granites must be extensive in size and have high heat flows, and often have natural permeability in the form of fault zones.
• In the UK, four areas satisfy these criteria: south-west England, northern England, the Scottish Highlands and the Mourne Mountains of Northern Ireland. The areas with the currently identified best potential lie in the south-west and north of England.
• To date, the only exploited resource for heat and power is found in the south-west of England.