Unlike the previous Hot Dry Rock research project carried out in Cornwall in the 1980s, UDDGP planned to target a permeable geological structure called the Porthtowan Fault Zone, which lies approximately 800m to the southwest of the United Downs site and is estimated to be around 300m wide. This has been achieved by successfully drilling two deep holes (wells) into the fault zone; one for injection at a depth of 2,393m and one for production at a depth of 5,275m, which is the deepest onshore well in the UK. The temperature at the bottom of the production well is expected to be about 190 ˚C.
Water will be pumped from the production well, fed through a heat exchanger and then re-injected into the ground to pick up more heat from the granite in a continuous cycle. The extracted heat will be used to supply a demonstration power plant.