Commodity watch by senior policy officer, Chris Osborne
There are many small thermal, hot mineral springs in the UK, the best examples in Bath, Buxton and Harrogate. Thermal springs are a natural phenomenon which occur where hot water from great depths in the earth, rise to the surface. In the UK, groundwater normally has a temperature around 10-12°C.
As you go deeper underground, the temperature increases due to heat stored in the earth, originating from when the earth was formed and from radioactive decay of minerals. This is known as the geothermal gradient. Subsurface temperature generally increases by 26° C for every km increase in depth, but this varies locally depending on the thermal conductivity of the rock. As the temperature of the earth increases with depth, so too does the temperature of the groundwater.
Here, Department for the Economy (DfE) in their ‘Energy Strategy: The Path to Net Zero’, has recognised the role of geothermal energy in the renewable heating and cooling of buildings in Northern Ireland.
What is geothermal energy?
Geothermal energy is available 24 hours a day, providing ‘always on’ renewable energy. Different technologies are available to harness the heat, including drilling into the ground. Water is brought to the surface with the energy from the heat transferred and sometimes warmed to the optimum temperature, using a heat pump. The heat exchange processes can also operate in reverse and transfer excess heat back to the subsurface to cool buildings.
Crucially, it can also be used in electricity generation.
Shallow v deep geothermal systems
Shallow geothermal energy is the low-grade heat (10-25°C) which is stored in the shallow subsurface at depths of up to 500m, and can be accessed in most locations using a ground source heat pump.
Deep geothermal energy is the heat stored at depths greater than 500m. Temperatures within the earth increase with depth in line with the local geothermal gradient. Average UK subsurface temperatures at 1000m are around 40°C, which is high enough to provide heat directly for space and hot water heating, without requiring a heat pump.
Geology of NI
A recent study by Geological Survey Northern Ireland (GSNI) has identified areas with the greatest potential for geothermal in the country. Sandstones present around Belfast rank highly in terms of geothermal potential. The same rocks are present elsewhere and buried to greater depths in parts of NI where the waters within the sandstones will have potential to be a deep geothermal resource. The area around Antrim is one such region with deeply buried sandstones.
In 2022, DfE set out a commitment to developing and commencing delivery of a geothermal demonstrator project as part of its pathway to reaching key decarbonisation targets by 2050. On 9 September, the UFU rural enterprise committee visited the GeoEnergy NI Project and Discovery Centre on the Stormont Estate, home to one of two geothermal test sites in NI.
GeoEnergy NI demonstrator project
DfE along with the GSNI are overseeing this project alongside a specialist contractor at two key locations in NI, chosen as they directly cover what is known to be one of NI’s most widespread and productive areas.
- Stormont Estate site – This aquifer is present at shallow depths under the Stormont Estate, and should be able to support a ground source heat pump system. It is hoped the project will result in a future geothermal heat network that will replace the current fossil fuel heating systems at some of the Estate buildings.
- CAFRE Greenmount Campus site – Greenmount was chosen because it lies above deeply buried porous sandstones, which are likely to contain naturally occurring hot water at deeper levels, c.70 °C. This deep aquifer is an exciting geothermal energy source and presents an opportunity to explore the future development of a geothermal district heating network or, potentially, and significantly for agriculture, the decarbonisation of horticulture. Greenmount Campus is home to the horticulture centre, with a glasshouse which covers an area of 2000m2 and a geothermal link could be a perfect fit.
Conclusion
NI could benefit from a more diverse range of renewable energy sources and this includes geothermal. This demonstrator project if successful, could potentially lead to the development of a policy/regulatory framework that supports and promotes opportunities to unearth NI’s geothermal potential, leading to economic development with job creation and establishing an knowledge base through academic and engineering excellence.
