Geothermal energy is a source of renewable energy that capitalises on the earth’s natural heat. Widely used around the world, geothermal energy provides 24/7 power, unlike most other renewable sources, because it does not depend on specific weather conditions.
In Cornwall, geothermal is enabled by the heat-producing granite that sits underneath much of the area.
GEL’s United Downs powerplant, the UK’s first operational powerplant to generate electricity from geothermal resources – is a binary plant. Binary plants use the hot geothermal brine to vaporise a secondary ‘working fluid’ that drives the turbine and generator. The technology is mature and has been in use for over 50 years.
Deep geothermal
Geothermal heat can be accessed in a number of ways, but a deep geothermal well is required to produce energy.
The above is a schematic [Wells and heat network diagram August 2023] of a geothermal doublet that has been drilled into a natural granite fault zone in Cornwall. A doublet is made up of two wells: one production well and one injection well. To harness the geothermal energy, the natural hot water at the bottom of the deeper well must be pumped up the production well, utilised at the surface, and then reinjected into the fault zone through the injection well. This ensures the hot reservoir is recharged over time.
The exact design of a geothermal doublet will depend on the geological environment. In Cornwall, GEL has designed a system with a shallow injection well to allow the reinjected fluid to percolate down through the rock over time to heat up, before being pumped back to the surface through the production well.
In the US, investment into geothermal has been significant, with many big tech companies also investing into the sector as a source of 24/7 renewable energy that can be harnessed for energy-hungry technologies.
Countries like Iceland and the Netherlands use geothermal for heat, rather than electricity.
