There is a delightful irony that the legacy of the dirtiest of fuels, coal, now has the potential to deliver a low carbon energy future.
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| (Wikipedia Commons) |
Abandoned coal mines seem incredibly promising due to their networks of flooded galleries and shafts lying at depths of up to several hundred metres below the surface. One can be almost certain that the water flow necessary for deep geothermal wells will be found in these flooded underground voids. The risk of not finding flowing water underground can inhibit deep geothermal developments elsewhere.
The volume of coal extracted compares to an equivalent void volume underground. On this basis (once allowing for subsidence), we estimate that the abandoned mines of the UK contain around two billion cubic metres of water at temperatures which are constantly around 12-16°C, and in some instances higher still. If heat corresponding to a 4°C temperature drop was removed from this volume, around 38,500TJ of heat could be liberated. This conservative estimate could provide enough heat for around 650,000 homes nationally.