Development of hot-dry-rock geothermal systems in the UK

Geothermal developments in the UK are constrained by the stable nature of the local geological regime. However, underground temperatures of over 200°C have been predicted at 5000 m under parts of South-West England and, potentially, elsewhere in the country. Exploitation of this heat source as a possible means of power generation requires the development of a process to sweep water through the rock mass between an injection point and a pattern of recovery wells. This method of exploiting geothermal energy is known as the hot-dry-rock process. Work has been underway in Cornwall to study the geotechnical problems influencing the creation of a sufficiently large heat transfer system. A three-well system reaching a depth of 2600 m has been in operation for over 10000 h with a maximum downhole temperature of 100°C. The system has been changing throughout the experiments, and the trends show that the necessary targets for viable operation should be attained in the near future. The results have been extrapolated to full commerical scale and show that generation costs of 3–4 p/k Wh are attainable with the current technology at favourable sites. Future developments to reduce costs substantially by reducing the number of wells needed for the operation, make hot-dry-rock worthy of serious attention as a potential source of power.