Subsurface heat, often referred to as geothermal heat, is the naturally occurring thermal energy stored beneath the Earth’s surface. It is created and sustained by the decay of radioactive elements in the Earth’s crust and the residual heat from planetary formation. In the UK, this resource offers a dependable, consistent source of low carbon heat that can support national efforts to decarbonise heating across residential, commercial, and public sector buildings.
Understanding Subsurface Heat
The temperature of the ground increases steadily with depth. This rate of increase is known as the geothermal gradient and in the UK typically ranges from 25°C to 35°C per kilometre. This gradient means that at realistically achievable depths (between 1,000 and 3,500 metres), the subsurface can provide a reliable heat source at useful temperatures for heating networks and industrial use.
Subsurface heat can be harnessed at different depths depending on the application. Shallow systems (less than 400 metres) typically support ground source heat pumps for individual buildings or small developments. Medium-depth systems (400–2,000 metres) are suited to district heating. Deep systems (over 2,000 metres) can supply higher temperatures and may be capable of supporting combined heat and power generation, depending on the geology and heat transfer conditions. The higher the temperature of the heat from the ground the less supplementary heat needs to be added to raise it to a useable temperature.
Why Subsurface Heat Matters
In the UK, approximately 44% of energy use goes towards heating, with the sector accounting for more than a third of greenhouse gas emissions. Most of this demand is met by burning natural gas. Meeting net zero targets by 2050 requires a fundamental shift in how heat is produced and delivered. Subsurface heat provides a scalable, secure and clean solution. It operates independently of weather and daylight hours, making it more predictable than solar or wind energy. Once installed, geothermal heating systems deliver consistent heat over many decades with very low operating emissions and minimal disruption. They are particularly well suited to applications where a constant heat supply is required, such as hospitals, schools, commercial estates, and residential districts.
Geological Potential Across the UK
Although not as volcanically active as other parts of the world, the UK still has considerable geothermal potential. According to a study by Durham University, there is enough geothermal energy stored underground to meet the UK’s heating demand for at least a century. Whilst shallow options are generally available across the UK, specific regions, such as the North East, North West, Midlands, Southern and South West England, present strong opportunities for commercial deep geothermal development.
Urban areas located above suitable rock formations with aquifer systems are particularly promising for medium and deep geothermal heat extraction. In these locations, geothermal energy can be used to serve district heating systems, reducing reliance on gas and improving long-term energy security.
How Geothermal Systems Work
Harnessing subsurface heat involves drilling into the Earth’s crust to access heat-bearing geological formations (a process that is well proven following decades of very similar oil and gas development in the UK). There are two main methods used for capturing heat: closed-loop and open-loop systems.
Closed-loop systems circulate a heat transfer fluid through a sealed network of pipes underground. As the fluid moves through the system, it absorbs heat from the surrounding rock and returns it to the surface for use in heating systems. This method is commonly used in areas without access to water-bearing rock formations.
Open-loop systems draw water from underground aquifers, pass it through heat exchangers at surface (to extract the heat), and return it to the ground. This approach is typically more efficient but depends on the presence of suitable groundwater flows and local environmental permissions.
Star Energy’s Role in Subsurface Heat Development
Star Energy has extensive experience in subsurface engineering through its history as a leading onshore oil and gas operator. The company manages over 90 sites across 28 fields, producing oil and gas from the East Midlands and the Weald Basin. This operational background provides a strong foundation for geothermal development, using similar drilling and resource management techniques.
In recent years, Star Energy has been developing commercial geothermal projects in the UK. This includes its acquisition of GT Energy in 2020 and a growing portfolio of feasibility studies and live developments.
Notable projects include a collaboration with Bring Energy to assess the potential for expanding geothermal heating in Southampton. Star Energy is also working with Veolia to develop large-scale systems for campuses, hospitals and commercial networks. These partnerships highlight the company’s shift towards delivering low carbon heat through practical, site-specific geothermal installations.
Long-Term Benefits of Subsurface Heat
One of the major advantages of geothermal systems is their low lifecycle carbon footprint. Once operational, emissions are limited to the power required for pumping the geothermal fluid to surface, often powered by low carbon electricity. As a result, subsurface heat is highly attractive to public and private sector organisations seeking to meet sustainability targets without compromising reliability.
The systems also require relatively low maintenance and provide stable energy prices over the long term. Because they are not dependent on imported fuels, they help insulate end-users from volatility in global energy markets.
For towns and cities with ageing gas infrastructure or grid limitations, geothermal heating offers a future-proof alternative. It reduces the strain on electricity grids, supports local resilience, and complements other renewable energy technologies.
Subsurface heat represents a critical opportunity for the UK to decarbonise its heating sector. With sufficient geothermal energy resources to meet national demand for decades, and with established technologies available today, there is a clear case for accelerating the development of subsurface heat infrastructure.
Star Energy is uniquely positioned to lead this transition. Drawing on its long-standing expertise in subsurface operations, the company is investing in projects that deliver low carbon heat across the UK. Through strategic partnerships and ongoing innovation, Star Energy aims to make geothermal energy a cornerstone of Britain’s energy future.