Geothermal energy is stored in the form of heat beneath the Earth’s surface.
There are 2 types of geothermal technology.
Deep geothermal for direct heat use
This is where the source of the heat tends to be hot water aquifers, which are rock strata containing groundwater at depths where temperatures are considerably hotter than the surface. This water can be extracted and will naturally replenish. At temperatures of over 60°C the heat can be used for local heat networks or for cooling through the use of absorption chillers.
Deep geothermal power
This is generally created when cold water is pumped down one borehole, heated up as it moves through fractures in hot rocks (at temperatures over 120°C) and returned to the surface via another borehole to drive an electricity-generating turbine.
One advantage of deep geothermal energy is that, aside from the initial drilling, geothermal plants have little visual, noise or air quality impact. They can also run almost continuously, providing baseload energy, and are not affected by changes in the weather.
The International Energy Agency predicts that by 2050 geothermal electricity generation could account for around 3.5% of global electricity production, with deep geothermal heat meeting 3.9% of projected final energy demand for heat.
In some locations (mainly in volcanic regions like Iceland and New Zealand) high temperatures are found at shallow depths or at the surface. It is these regions that have the vast majority of deep geothermal plants.
Deep geothermal potential in the UK
The UK does not have the resource potential of volcanic regions like those in New Zealand and Iceland, but in some locations underground temperatures have the potential for deep geothermal projects. These are at depths of:
- over 1km for heat only projects
- 4 to 5km for power projects
As depths increase so does the uncertainty, complexity and therefore risks (of failed boreholes) and the expense of projects.
Heat-only projects are generally considered to have the greatest potential in the UK because the resource is more widespread and shallower. This includes the hot aquifers (ie subterranean bodies of water) in the North East, Wessex, Cheshire, and Northern Ireland.
The UK’s only existing geothermal heat-generating station (heat only) is at Southampton, where an 1800 metre borehole taps into the edge of the aquifer under Wessex and provides heat to the Southampton district heat network. The borehole is being refurbished.
Find out about Southampton’s geothermal energy district heating scheme.
There is no deep geothermal power generation in the UK.
The granite regions of South West England, the Lake District and Weardale and the Eastern Highlands of Scotland are considered most likely to have the best prospects for power generation.
Our support for the geothermal industry
Renewables Obligation (RO)
Power generated from geothermal sources is eligible for support under the RO at a tariff of 2 Renewables Obligation Certificates (ROCs) per megawatt (MWh) generated.
Renewables Heat Incentive (RHI)
Deep geothermal heat for direct use also benefits under the RHI. The RHI also applies to geothermal cooling systems.
In September 2012 we published a consultation on proposed revisions to the non-domestic RHI. If approved in Parliament it will create a separate and higher tariff for deep geothermal heat. Previously the technology was grouped with ground source heat pumps at a lower tariff.
City Deals programme
In March 2011, the Department of Energy & Climate Change (DECC) published the Strategic Framework for Low Carbon Heat in the UK, which identified deep geothermal as an important source of renewable heat for urban networks.
Through the City Deals programme, certain cities are being helped to develop plans for heat networks.
We will provide around £1 million to these cities to undertake feasibility studies on new heat network projects. This includes Manchester and Newcastle, which have both identified deep geothermal energy as a possible heat source for their networks.
Regional Growth Fund
In 2010 the Department for Business Innovation & Skills (BIS) awarded the United Downs project in Cornwall a £6 million grant from the second round of the Regional Growth Fund.
For more information about the fund, see our policy on boosting private sector employment in England and our detailed guide on understanding the regional growth fund.
Deep Geothermal Challenge Fund
DECC has provided more than £4.5 million in grants to support the following projects through the Deep Geothermal Challenge Fund:
- United Downs near Redruth, Cornwall – £1.475m in 2009
- Eden Project near St Austell, Cornwall – £2.011m in 2009
- Southampton City Centre – £200,000 in 2010.
- Eastgate in Weardale, County Durham – £461,000 in 2009
- Science Central site, Newcastle City Centre – £400,000 in 2010
On 30 May 2011, we signed a Memorandum of Understanding with the Icelandic government on a number of energy issues, including supporting the development of deep geothermal energy in the UK.