Different types of geothermal energy can be harnessed in different ways, but in general it will require drilling into the Earth to reach natural reservoirs of hot water.
To the right is a schematic of a geothermal doublet into a natural 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 hot water at depth must be pumped up the production well, utilised at the surface and then reinjected into the reservoir 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 have designed a system with a shallower injection well to allow the reinjected fluid to percolate down through the rock over time and heat back up before being pumped back to the surface through the production well.