Keeping warm: a review of deep geothermal potential of the UK

In 2015, the primary energy demand in the UK was 202.5 million tonnes of oil equivalent (mtoe = 848 EJ). Of this, about 58 mtoe (2.43 EJ) was used for space heating. Almost all of this heat was from burning fossil fuels either directly (50% of all gas used is for domestic purposes) or indirectly for power generation. Burning fossil fuels for heat released about 160 million tonnes of carbon dioxide in 2015. The UK must decarbonise heating for it to meet its commitments on emissions reduction. UK heat demand can be met from ultra-low-carbon, low enthalpy geothermal energy. Here we review the geothermal potential of the UK, comprising a combination of deep sedimentary basins, ancient warm granites and shallower flooded mines. A conservative calculation of the contained accessible heat in these resources is 200 EJ, about 100 years supply. Presently only one geothermal system is exploited in the UK. It has been supplying about 1.7MW(T) (heat) to Southampton by extracting water at a temperature of 76 degrees C from a depth of 1.7 km in the Wessex Basin. Like Southampton, most of the major population centres in the UK lie above or adjacent to major geothermal heat sources. The opportunity for using such heat within district heating schemes is considerable. The consequences of developing a substantial part of the UK's geothermal resource are profound. The baseload heating that could be supplied from low enthalpy geothermal energy would cause a dramatic fall in the UK's emissions of greenhouse gases, reduce the need for separate energy storage required by the intermittent renewables (wind and solar) and underpin a significant position of the nation's energy security for the foreseeable future, so lessening the UK's dependence on imported oil and gas. Investment in indigenous energy supplies would also mean retention of wealth in the UK.