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The earth’s crust contains a virtually limitless amount of thermal energy which is being continuously replenished from the mantle below it. As a result, the temperature increases at an average rate of about 25ºC for every 1,000m of depth.

In volcanic areas and at some tectonic plate boundaries the temperature gradient is much higher and, where this coincides with suitable geology, underground reservoirs of steam or hot water can develop. These can be tapped by drilling to bring the energy to surface where it can be used for electricity generation.


Lower temperature resources are used for direct heating and industrial or agricultural processes in 90 countries around the world and developers are now drilling deeper wells in non-volcanic areas to access the temperatures they need because they recognise the environmental benefits of the technology. It is a clean, sustainable, renewable, low carbon energy source that has a very small surface footprint and minimal environmental impact.

In the UK, shallow resources can be harnessed using Ground Source Heat Pumps almost everywhere. Moderate depth resources, between 500m and 2500m, can be found in many places, where rock temperatures between 30˚C and 100˚C make them suitable for direct heating applications.

Deep resources exist in some parts of the country, most notably in Cornwall and west Devon, where high geothermal gradients make it possible to generate electricity as well as supply heat.


Wherever there is a need for heat, geothermal can provide a solution.

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