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Geothermal energy is the energy stored in the form of heat beneath the Earth’s surface that can be used either for heating or to generate electricity. Geothermal energy plants are normally located in regions where there is volcanic activity, such as in Iceland where geothermal energy provides around two-thirds of the country’s primary energy demand. Geothermal resources can either be used for heating, or for the generation of electricity, or both.
Geothermal resources in the UK
Ground source heat pumps
In the UK, there is a resource of geothermal energy at shallow depths which can be exploited with ground source heat pumps (GSHPs). GSHPs use pipes which are buried to extract heat from the ground. The upper 10–15 m of the ground is heated by solar radiation and acts a heat store.
This heat can then be used to heat radiators, underfloor or warm air heating systems and hot water in homes. Ground source heat pumps are supported by the Government Renewable Heat Incentive (RHI) scheme which provides payments for consumers who install and use renewable heating technologies. At the end of April 2018, a total of 9,107 applications for domestic ground source heat pumps had been accredited under either the RHI or its predecessor scheme. In addition, 887 non-domestic water or ground source heat pumps had been accredited to April 2018.
Deep geothermal plants
With increasing depth, the ground temperatures are no longer affected by the sun and are instead warmed by heat from the Earth’s core. The UK has no active volcanoes, but it does have several geological features that have potential for geothermal energy.
The British Geological Society’s (BGS) page on Geothermal Energy – what is it? contains further information and a heat flow map of the UK (heat flow is the movement of heat in the Earth and is higher in areas with greater geothermal potential).
There are some geothermal projects planned in the UK, for the generation of heat, electricity, or both. There is also a commercial plant in Southampton which in 1986, began delivering heat from a borehole to a district heating network, and is now operated by the energy firm ENGIE. ThinkGeoEnergy, a news and blogging website focusing on the Geothermal industry in the UK, has a list of projects.
Both ground source heat pumps and deep geothermal plants can be connected to heat networks: a distribution system of insulated pipes that carry hot water to homes or businesses. These networks can also use heat from other sources such as industry and combined heat and power plants. The Government offers funding to support heat networks.
Total resources estimates
A number of studies have been undertaken on the geothermal potential of the UK, some examples are listed below. The estimates vary due to the areas of the UK being considered, the depth of drilling considered, and the extent to which the resource is deemed technically and economically recoverable.
- The geothermal potential of the UK was investigated by a program funded by the UK government and the European Commission that ran from 1977-1994 and identified the key heat flow areas of potential in the UK (see BGS website for details).
- In May 2012, a paper by consultants SKM in association with the Renewable Energy Association (an industry trade body) argued that geothermal power could provide 20% of the UK’s electricity and all of the UK’s heat demand.
- In 2013, a Government commissioned Deep Geothermal Review Study by the consultancy Atkins concluded a lower figure of 4% of annual electricity requirements (in 2013 figures).
- In 2017, a study estimated that the UK had enough resource that was ‘theoretically available’ to easily surpass all UK energy demand (in 2015) but the amount that was ‘technically available’ was much smaller than the ‘theoretical’ resource and recovery would depend on depths drilled and areas targeted.
Government views on geothermal power
On 4 June 2018, during an adjournment debate on Geothermal Energy: Clackmannanshire, the Minister for Clean Growth Claire Perry set out the Government’s view on Geothermal energy:
That brings me to the role of geothermal energy, which is a critical part of the renewable energy resource. It can be used in several ways, for example heat networks. The UK Government have set aside over £300 million to invest in district heat networks over the next few years. They are a really important way of bringing it forward. Deep geothermal power is another opportunity to create heat and generate power […]
This is not about finding new resource. The mining legacy has created a lot of holes in the ground beneath our feet, which have filled up with water. The water has become heated and is now available without drilling deep wells. This is relatively easy to set up. I am proud to be working with the Coal Authority and others to consider how we might manage this mining legacy. Across the UK, it has recently been assessed that there are over 2 million GW hours of low carbon energy stored in mine workings across the UK. I feel strongly that we should be looking at how to extract it.
As I said, there are several ways to use this very valuable resource. We can use it as heat to supply homes and businesses. It can help to deliver the clean growth aspects of our industrial strategy, because it can be used to provide heat to certain business sectors. It can also provide opportunities for energy through regeneration and storage. There is a lot of work being done on storage capability. The problem with renewables is that they can be very intermittent. How do we store energy in a liquid state? Deep networks could be a way to help us to lead the world on this going forward. We are looking across the UK to see how we might exploit this great resource.
The Scottish Government have information on their support for geothermal power on their webpage on Geothermal Energy.
Geothermal power is eligible for support under the Contracts for Difference subsidy scheme auctions, though no projects have yet been successful. The Government also have previously supported Geothermal through funding, such as the Deep Geothermal Challenge Fund.
 Jon Busby and Ricky Terrington, Assessment of the resource base for engineered geothermal systems in Great Britain, Geothermal Energy, vol 5, 24 February 2017