Geothermal energy: a potential source for decarbonising the hospital estate

Geothermal energy occurs across the UK, mostly in deep, onshore sedimentary basins. Where groundwater circulation occurs within deeply buried rocks (1 to 3 km), it forms hydrothermal systems or deep geothermal aquifers, also called ‘hot sedimentary aquifers’.

Hydrothermal systems arise from a combination of three geological components: fluid, heat and permeable rocks. Temperatures within the basins are generally 40 to 60°C but could reach 100°C in the deepest parts of some of the basins (Busby, 2014), hence these systems are most suited to provide direct-use heating (without use of a heat pump) for district heating, horticulture or industrial process heat.

BGS has undertaken detailed mapping and investigation of this resource since the 1980s and estimates that the geothermal heat resource contained within these basins is one hundred to two hundred times the UK’s domestic heat demand (Busby, 2014). However, as heat cannot currently be transported over long distances because of high distribution losses along the way, opportunities for developing geothermal heat are limited to areas of high heat demand, such as cities. Many major population centres in the UK lie above or adjacent to sedimentary basins.

Exploitation of these deep geothermal systems requires the drilling of two or more deep wells (typically 1 to 3 km) to reach the higher-temperature heat resources. This heat can be used directly to supply heating to users with large heat demands, including hospitals, domestic or commercial space heating or industrial users.

Geothermal technologies are scalable and combinable across the spectrum of drillable depths and temperatures. In some cases, for example, heat pumps are being used in conjunction with moderately deep wells (500 to 1000 m) to boost temperatures and achieve the required operational temperatures for the heat network. Such hybrid systems benefit from higher temperatures at depth whilst avoiding the high capital costs and risks associated with even deeper drilling.

Where a good resource exists, geothermal can supply district heating at the city scale. For example, Paris receives geothermal heating from its deep geothermal aquifer for around 250 000 homes via 50 heat networks. Around 50 000 homes in Munich are supplied with geothermal heating, saving about 75 400 tonnes of carbon dioxide (CO₂) per year compared with natural gas (Abesser and Walker, 2022).

The image above shows the sedimentary basins (yellow, blue and green areas on the map) where deep geothermal prospects exist in England. Also shown on the map are locations of NHS hospitals that have been prioritised for decarbonisation because of their high heat demand. An initial assessment suggests that, out of the 210 sites, 109 overlie potential geothermal aquifers. The estimated drilling depths to reach a temperature of 50°C range between 1.2 and 3 km. Developing geothermal projects for these sites could save between 1.3 and 22.7 Kt CO₂ equivalent emissions per year for individual hospital sites.

It is important to note that image above only shows the extent of the geothermal basins and that there is great variability in terms of the reservoir properties and temperatures within individual basins. Further analyses, in form of a more detailed feasibility study followed by site-specific investigations, are required to assess the feasibility of geothermal exploitation at any particular site before any drilling takes place.

Further information
In the first instance see the White Paper that BGS have issued on Geothermal energy which is summarised on the BGS site.

To find out more about feasibility for using geothermal energy at your site, please contact enquiries@bgs.ac.uk. For further information about geothermal energy, see Abesser and Walker (2022).

Corinna also shared some links that might be of interest to see operational projects in Europe (some pages are in Dutch or Spanish but automatic translate in Microsoft Edge or Google Chrome works well):

Operational Projects in the Netherlands

Map and operational projects in Germany (mainly in Munich area)

In the Paris basin multiple projects have been operational for decades. A recent project put in operation including service to hospitals is in Esson

In Spain mine water has been used for years now for district heating (6 MWth), including a regional hospital, info is in Spanish but automatic translation pretty accurate

About the author
Dr Corinna Abesser is the head of geothermal energy research at BGS. She contributes to national and international research and acts as an expert advisor to the UK Government and Parliament. She has developed several briefing papers on the topic of geothermal energy for policymakers and parliamentary audiences.

References
Abesser, C, and Walker, A. 2022. Geothermal Energy. Parliamentary Office for Science and Technology Research Briefing, PostBrief 46. Available from https://post.parliament.uk/research-briefings/post-pb-0046/
Busby, J P. 2014. Geothermal energy in sedimentary basins in the UK. Hydrogeology Journal, Vol. 22, 129–141. DOI: https://doi.org/10.1007/s10040-013-1054-4