United Downs is the UK’s first commercial deep geothermal electricity generation project. It consists of two wells, drilled at different depths into hot rocks found deep beneath the surface. The production well is 5.1km deep, the deepest well in the UK and almost four times the height of Ben Nevis. The temperature at the bottom of the wells is ~175°C. To produce electricity, water is fed into the injection well. When it reaches the bottom, it filters through cracks in the hot rocks, absorbing heat until it reaches the base of the production well. The water is then pumped back up to the surface where it is passed through a heat exchanger containing a fluid with a very low boiling point. The heat from the water is transferred to the fluid, converting it to steam. This steam is used to turn a turbine which generates clean electricity. The remaining cool water is then pumped back into the injection well to go round the system again in a closed loop.
United Downs geothermal will generate clean electricity 24 hours a day, enabling it to provide baseload electricity to the grid, an essential part of net zero energy system. It has the potential to generate electricity and also provide renewable heat for local use.