Skip to main content
Durham Energy Institute
Walney Sunset Hero Crop 2000 x 800

What is Geothermal Energy?

Geothermal energy comes from heat produced at the Earth’s core. It is normally associated with volcanic regions e.g. Iceland or New Zealand.

Volcanoes are not essential for geothermal energy.

Away from volcanic regions, most countries can access geothermal albeit at lower temperatures. Temperature increases by 25-30°C with each km depth. This means that a well drilled to 2km would reach a temperature of 50-60°.

The key thing is finding water at depth that is essential for bringing heat to the surface heat to the surface. Durham University is researching the UK potential for geothermal energy to decarbonise heat.

Why is heat important?

Over half of UK energy demand is used to produce heat. Most of this is produced using gas. We currently import more than half of the gas we use. This raises concerns about climate change and future energy security. We need to find alternative sources of low carbon heat.

Where is the heat located?

The UK has a range of geothermal settings:

Deeper than 1km, temperature 35°C or more

  • Sedimentary basins
  • Radiothermal granites
  • Buried cave (karst) formations
  • Onshore and offshore hydrocarbon wells

Shallower than 1km

  • Flooded abandoned mines 12-20°C

Heat from abandoned mines

Abandoned mines across the UK are flooded with water that can be used to heat homes.

Abandoned mines are shallower and cooler than deep geothermal systems. This means that development risks are significantly reduced because we know former mining infrastructure can flow water through existing tunnels and shafts.

The UK has 23,000 flooded abandoned coal mines and 25% of the built environment lies above abandoned coal mines.

In addition to providing low carbon, secure energy this can bring economic and social improvements to regions that suffered following the abandonment of deep mining in the UK.

We are working with local authorities, local communities, Parliament, the Coal Authority and industry to explore options for geothermal energy in the North East of England.

 

How much heat is down there?

The UK's geothermal resources could meet the UK heat demand for over a century. Using it will need changes to how we supply and use energy.

Existing buildings would change their heating systems to use geothermal energy. The UK has one proven deep geothermal energy system in Southampton.

Why aren't there more geothermal systems?

Risk is the biggest barrier to geothermal development. The technology exists to drill wells but it is difficult to predict how much water is present at depths of over 1km.

Abandoned mines are lower risk. Although they are shallower and cooler we know water can flow through tunnels and shafts. Abandoned mines are a good opportunity for UK geothermal because risk is reduced. Also, it uses existing infrastructure that people worked hard to create.

 

Further information and resources