The UDDGP project aims to prove the technical and commercial viability of generating electricity from geothermal energy in Cornwall. So if the drilling and testing is successful we will build a small demonstration power plant and supply power to the grid.
Our base case is a 1MWe plant, enough to supply about 1500 homes. But if testing shows that the wells could supply more than that, and if additional funding is available, we could consider increasing the size to 3MWe, which is the limit of the available grid connection. This is still a very small power plant but it would serve to demonstrate the concept and assess longer term sustainability and operating costs.
The final design will depend on the testing results and procurement but it is most likely to be a binary power plant, the image below shows an example of this system in which the water from the wells circulates in a closed loop and heat is transferred to a secondary working fluid that drives the generating equipment.
This photo is of a 4.8MWe geothermal power plant in Insheim, Germany. It is slightly larger than the power plant we envisage at United Downs, but of a similar type.
It is supplied by water pumped from a production well drilled to a depth of 3,600m where the water temperature is 160 degree Celsius. As with United Downs, the heat is transferred to a working fluid which supplies the power plant, before being reinjected into the ground. The system operates at circulation rates between 50ls and 80l/s. The plant has been operational since 2012.
This plant is air-cooled, which is one option for United Downs. The other option is for water cooling, in which case the cooling fans would be replaced by small cooling towers.