As the UK’s demand for clean, sustainable energy increases, it is crucial to diversify energy sources to meet varying needs and reduce reliance on fossil fuels. Geothermal energy, in particular, stands out for its reliability, low emissions, and ability to provide consistent power. The science behind geothermal energy relies on the constant, reliable heat within the Earth’s crust. The Earth’s internal heat is generated by both the residual warmth from the its formation and the ongoing radioactive decay of elements within the crust. This provides a stable and continuous source of energy, making it an ideal option for addressing energy demands.
The general process used to generate geothermal energy involves several key steps:
- Wells are drilled into the earth to access underground reservoirs of hot liquid (usually water) or steam.
- This heated fluid is pumped up to the surface.
- This steam or hot liquid will be used to rotate a turbine.
- The turbine’s motion will activate a generator, which produces electricity.
- The liquid/steam will then be reinjected into the reservoir.
By capturing this heat efficiently and reinjecting the cooled water back underground, geothermal energy provides a sustainable and low-emission source of power.
Different types of power plants are used to convert geothermal heat into energy. The type of geothermal plant in use depends on the state of the subsurface fluid and its temperature. Each of these relies on this process, but utilises slightly different mechanisms. The most common is a flash steam plant, where hot water above 180°C is brought to the surface, causing a pressure drop that turns it into steam. Another common type of plant is a dry steam plant, where the underground steam can be accessed directly. Binary cycle plants, where the heat from geothermal water vaporises a secondary fluid with a lower boiling point. This means geothermal energy can be generated in areas with moderate geothermal gradients.
Geothermal power plants are typically located in regions with a high geothermal gradient, where the rate of increase in temperature per unit depth in the Earth is unusually high. Areas where this might occur include tectonic plate boundaries, volcanic zones, or hot springs and geysers. However, away from these regions, geothermal energy can still be accessed by utilising deep geothermal at lower temperatures, and by shallow geothermal. Here, the shallow, upper crust of the ground is heated by the sun and acts as a heat store. Ground source heat pumps can then extract this. One of the most high potential uses of this in the UK is through mine water geothermal systems, which repurpose abandoned mines. These flooded mine shafts contain water naturally warmed by the surrounding rock. At depths of around 1km, temperatures can reach 40°C, providing a viable source for energy production. This approach is especially relevant in regions like Durham, where a legacy of coal mining provides unique opportunities to tap into this renewable resource. By leveraging existing infrastructure, mine water geothermal offers a sustainable solution that reduces environmental impact and contributes to regional energy independence.
Geothermal energy in the UK remains an underutilised resource, currently meeting just 0.3% of the national heat demand as of 2021. Currently, the most common use in the UK is to regulate the temperature of individual properties through heat pumps.
The Durham Energy Institute has identified 45 sites in the UK with deep geothermal potential, and it is estimated that the UK’s geothermal resources could meet the UK’s heat demand for over a century. Despite this, there are no clear national targets for developing deep geothermal technologies, partly due to a lack of clear regulations and unclear ownership rights over geothermal heat. Currently, geothermal heat is not classified as a “natural resource” like oil and gas, leaving no clear answer as to who owns the heat. There is also no regulatory system in the UK to manage the resource, and while general regulations such as environmental licensing and local planning apply, these do not manage the resource of heat itself. Without clear regulation, the UK risks missing out on a sustainable and reliable energy source that could play a key role in meeting its future energy and decarbonisation goals.
As the UK seeks clean, dependable energy sources, geothermal energy holds significant potential for the future. The advancements in technology, especially approaches like mine water geothermal, showcase how this renewable resource can be adapted to meet diverse regional needs. While still developing in comparison to other renewable technologies such as solar and wind, geothermal energy’s unique ability to provide a constant power supply positions it as an essential component of a sustainable energy mix.