Feliks, Michael E.J.

McCay, Alistair

Roberts, Jennifer J.

English

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 1 
CARBON INTENSITY OF DEEP 
GEOTHERMAL HEAT IN SCOTLAND 
SCOTTISH UNIVERSITY POLICY BRIEFING: MAY 2020 
AUTHORS 
Dr. Alistair McCay 
University of Glasgow 
Infrastructure and Environment 
alistair.mccay@glasgow.ac.uk 
Dr. Jen Roberts  
University of Strathclyde 
Civil and Environmental Engineering 
jen.roberts@strath.ac.uk 
Dr. Michael Feliks 
Hotspur Geothermal 
SUMMARY 
We analysed the carbon emissions from deep 
geothermal heat using the Hill of Banchory feasibility 
study as a case study. Our analysis [1] found that: 
▪Deep geothermal systems in Scotland can produce 
very low carbon heat that is compatible with 
Scotland’s carbon emission reduction targets for 
2045 and beyond. Deep geothermal heat systems 
therefore offer a long-term low-carbon heat 
option at scale. 
▪The carbon intensity of deep geothermal heat is 
between 9.7 and 14.0 kg(CO2e)/MWhth; this is ~5% 
of the value for natural gas heating. 
▪The carbon intensity of deep geothermal heat could 
be reduced further as follows: 
(a) Direct emissions:  
Drilling: replace diesel fuelled drilling apparatus 
with natural gas or electricity powered hardware. 
(b) Indirect emissions:  
Pump operation: decarbonise the power grid more 
rapidly than forecast, or substitute mains power 
with local renewable electricity to power pumps.  
Infrastructure: source lower carbon steel and 
cement.  
Land use change: design projects to minimise land 
use change emissions. 
In Scotland, no commercial deep geothermal heat (or 
electricity) project has yet commenced production. 
Other countries with comparable geothermal 
resources such as the Netherlands and France now 
have well developed geothermal heat sectors based 
on long-term, stable, policy support. 
 
 
BACKGROUND 
The Climate Change (Emissions Reduction Targets) 
(Scotland) Act 2019 sets 2045 as the net-zero 
emissions target year for Scotland. Heat currently 
accounts for 47% of Scotland’s emissions [2]. While 
Scotland’s electricity network is rapidly 
decarbonising, the proportion of heat demand from 
renewable sources in Scotland was only 5.9% in 2017; 
which is the lowest in Europe [3]. 
Deep geothermal heat (DGH) has been proposed as a 
technology option that could provide a significant 
amount of low carbon heat, assisting in the transition 
away from fossil fuel heating in Scotland [2, 4]. 
DGH resources in Scotland can be accessed by drilling 
1.5-3 km below ground and pumping hot ground- 
water (70-90°C) to the surface to be used for space or 
industrial heating. DGH resources are found in the 
granites of North East Scotland [5] and the deep 
sedimentary aquifers of the Central Belt [6].  
In 2015 the Scottish Government’s Low Carbon 
Infrastructure Transition Programme funded three 
DGH feasibility studies: two to assess potential for a 
granite-based heat resource and another to assess a 
sandstone-based resource [7]. The studies found no 
technical barriers to DGH exploitation in Scotland. 
However, as yet no commercial large scale deep 
geothermal project has commenced drilling in 
Scotland; the risk that the first borehole may prove 
unproductive is the primary barrier to progress. The 
Netherlands, which has geothermal resources similar 
to Scotland’s Central Belt, have overcome this barrier 
by developing a long-term support and legal 
framework, including an insurance scheme, which is 
supporting growth of its DGH industry [8]. 
To determine the potential for DGH to contribute 
towards net-zero targets, then the carbon intensity of 
deep geothermal heat must be known. A recent 
collaborative project between the Universities of 
Glasgow and Strathclyde, in partnership with industry 
experts Hotspur Geothermal, aimed to address this 
gap by performing a life cycle analysis of a deep 
geothermal heat project in Scotland.  
  
 2 
PROJECT OUTLINE 
Our study aimed to quantify the life cycle greenhouse 
gas emissions associated with producing DGH in 
Scotland. The study used DGH project details from 
the Hill of Banchory Geothermal Project (which we 
refer to as the ‘Banchory DGH project’), which was 
one of the three DGH feasibility studies funded by the 
Scottish Government’s Low Carbon Infrastructure 
Transition Programme. The Banchory DGH project 
would source heat from granite rocks 1.5 to 3 km 
below ground, located 1 km to the North of the town 
of Banchory in Aberdeenshire. Heat would be 
transported between the DGH site and the town’s 
existing (biomass-heated) district heat network via 
buried insulated pipes. The feasibility study found 
that the Banchory DGH project could produce around 
400,000 MWhth of heat over a 30-year lifetime. 
In our work we considered the direct and indirect 
greenhouse gas (GHG) emissions (expressed as CO2 
equivalent emissions, CO2e) associated with the 
development and operation of the Banchory DGH 
project. Our calculations accounted for GHG 
emissions from: land use change resulting from 
building the DGH infrastructure; drilling the 
boreholes; and from generating the power required 
to operate the pumps that extract and circulate the 
thermal waters over a 30-year lifespan. We also 
accounted for the indirect GHG emissions embedded 
in the manufacture and transport of the DGH 
hardware such as steel and cement. We did not 
account for the carbon embedded in the town’s 
existing district heat infrastructure. 
RESULTS 
We found an upper estimate for CO2e released over 
the project lifetime of 5,506 tonnes (t) CO2e. The 
largest contributor to the upper estimate (1,678 
t(CO2e), 30% of the total) was the indirect GHG 
emissions from operating the pumps that extract and 
circulate the thermal waters. Our calculations 
assumed the pumps were powered by the UK 
electricity grid which was decarbonising over the 30-
year lifespan at rates equivalent to energy emissions 
targets for 2030.  
The remaining emissions primarily came from the 
building of the site, including: 
▪ Indirect GHG emissions embedded in the steel 
casing of the geothermal boreholes: 1,296 t(CO2e) 
▪ Direct GHG emissions from powering the drill rig 
using diesel fuel: 1,243 t(CO2e) 
▪ Change in land use (from building on heath rather 
than grass or arable land): 841 t(CO2e) 
▪ Indirect GHG emissions embedded in the cement 
used to seal the boreholes: 360 t(CO2e) 
Other smaller emission sources included the indirect 
emissions embedded in the pipes used to transport 
heat, transporting the drill rig to and from the DGH 
site, and the fluids used for drilling the well.  
The lower estimate for the CO2e released over the 
Banchory DGH project lifetime was 3,806 t(CO2e). 
The calculated carbon emissions intensity of heat 
produced from the Banchory DGH project is 9.7–14.0 
kg(CO2e) per MWhth which is 5-7% that of fossil fuel 
derived heat. Thus, DGH offers very low carbon heat. 
Hypothetically, if all of Scotland’s heat were delivered 
by DGH, heat provision would take up less than 5% of 
a net-zero national carbon budget as set out in the 
The Climate Change (Emissions Reduction Targets) 
(Scotland) Act 2019. However, the total DGH 
potential for Scotland is still unknown. 
Our findings show that DGH should be considered as 
a technology option for reaching net-zero in Scotland. 
REFERENCES 
1. McCay, A.T., Feliks, M.E. and Roberts, J.J. (2019). 
Life cycle assessment of the carbon intensity of 
deep geothermal heat systems: a case study from 
Scotland. Science of The Total Environment, 
685,p.208-219. 
https://doi.org/10.1016/j.scitotenv.2019.05.311 
2. Heat Policy Statement, Towards Decarbonising 
Heat: Maximising the Opportunities for Scotland. 
The Scottish Government 2015.  
3. Annual Compendium of Scottish Energy Statistics. 
May 2019. Scottish Government 
4. Younger, P.L., Gluyas, J.G. and Stephens, W.E., 
2012. Development of deep geothermal energy 
resources in the UK. Proceedings of the Institution 
of Civil Engineers-Energy, 165(1), pp.19-32.  
5. McCay, A.T. & Younger, P.L., 2017. Ranking the 
geothermal potential of radiothermal granites in 
Scotland: are any others as hot as the 
Cairngorms? Scottish Journal of Geology, 53(1), 
pp.1-11.  
6. Gillespie, M.R., Crane, E.J. and Barron, H.F., 2013. 
Deep geothermal energy potential in Scotland. 
British Geological Survey Commissioned Report, 
CR/12/131, 129. 
7. Brownsort, P. and Johnson, G. 2017. Geothermal 
Energy in Scotland: A synthesis report covering 
four feasibility studies. Scottish Carbon Capture 
and Storage.  
8. Van Heekeren, V. and Bakema, G., 2015. The 
Netherlands country update on geothermal 
energy. In Proceedings World Geothermal 
Congress 2015 (pp. 19-24). International 
Geothermal Association Melbourne. 


Carbon Intensity of Deep Geothermal Heat in Scotland. Scottish University Policy Briefing: May 2020

http://eprints.gla.ac.uk/215016/1/215016.pdf

Carbon Intensity of Deep Geothermal Heat in Scotland. Scottish University Policy Briefing: May 2020

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