Can abandoned mines heat our future?

A guest post from Charlotte Adams, Assistant Professor at Durham University, who is currently leading work at Durham on the potential of abandoned mines to provide energy storage and a low carbon source of heat and cooling for the UK. She is also a Fellow of the Durham Energy Institute and a member of the University’s Carbon Management Team. She will be speaking on the topic at the Society’s upcoming Bryan Lovell Meeting, ‘The Role of Geological Science in the Decarbonisation of the UK’ which takes place on 22-24 January – find out more here.

The term “geothermal energy” conjures up images of geysers and volcanoes and it is true that the most productive geothermal sites are located in areas that are tectonically active, close to the Earth’s plate margins. Yet most of the global landmass is not near a plate margin, so what are the geothermal opportunities for intraplate settings? In the UK, we have a range of geothermal resources located within deep sedimentary basins, granites, hydrocarbon wells and more cryptically in our abandoned mining infrastructure. We have focused on the latter for its potential to de-risk geothermal. Although temperatures here are lower than for deep geothermal systems, we are more certain of water flow which is crucial for energy transfer.

An abandoned mine close to Port Mulgrave, North Yorkshire. (c. philld via http://www.geograph.org.uk)

A political decision during the 1980s to rapidly abandon UK collieries and switch off water pumps led to high levels of unemployment and social deprivation in mining areas. These communities were further affected by rising water levels underground which threatened surface and groundwater. Over the past couple of decades, extensive measures have been taken to maintain pumping in strategic locations to control rising water levels and intercept and treat any potentially problematic discharges from abandoned mines which has a cost to the UK taxpayer. At Durham University, we are exploring the opportunity to use the water within flooded abandoned mines to provide a source of geothermal heat for the future. This could also deliver economic opportunities to former mining areas.

The Maankwartier, Heerlen, Netherlands which is part of a network of buildings heated and cooled by minewater in the Netherlands. More information at www.mijnwater.com

Over half of UK energy demand is used to produce heat, most of this comes from burning gas and most is consumed by the domestic sector. The UK has been a net importer of gas for over a decade meaning that we now rely on gas supplies from other nations. This brings our long-term energy security into question. In addition to improving our energy security, we also need to decarbonise our energy supplies to meet carbon reduction targets and combat climate change. Over the past decade, around half of our electricity demand has been decarbonised using renewables and nuclear, yet around three quarters of our heat demand is still derived from fossil fuels.

Over 15 billion tonnes of coal were extracted from the UK subsurface over the past century. Spread over the entire UK land surface, this would create a layer of coal 5cm deep. Allowing for some post abandonment subsidence, it is estimated that there are around 2 billion cubic metres of water within flooded mines that contain around 2.2 million GWh of heat. There is also good overlap between coalfield areas and areas of heat demand. This is not surprising as many of our towns and cities were developed as a direct result of their coal reserves. Around one quarter of UK homes are located in coalfield areas meaning there is good potential to access this energy source.

The water within the mines is tepid, at temperatures of 12-20°C. Clearly this is not hot enough to take a bath in or heat a room but by using a heat pump, temperatures can be increased to a more comfortable 40-50°C. Although the heat pump requires an electrical input, it is an energy efficient device because you can expect to get 3-4 kW of heat output from the heat pump for every 1 kW of electrical input. This research has shown that we don’t need access to volcanoes to develop geothermal energy and that our abandoned mines can augment the UK’s geothermal resources which could in their entirety meet our heat demands for a century or more.

I was delighted to have the opportunity to present this research as part of the Geological Society’s Public Lecture Series in December 2018. My presentation can be viewed here: