What is Geothermal Energy?

Ask any gardener and they’ll tell you the ground contains heat.

The UK's average ground temperature is around 8-13 degrees Celsius all year round. This low level geothermal energy, built up in the ground during the summer months, is now being tapped into by ground source heat pumps as a source of renewable power.

To access geothermal energy, coils or loops of special grade pipe are buried in the ground either in horizontal trenches or vertical boreholes, usually in a garden or field. The heat pump, which looks a bit like a conventional boiler, actually works a bit like a refrigerator. It cools the water from the outside loop, and in doing so obtains heat for an internal heating loop, which feeds an underfloor heating system. The cold water is then circulated through the outside loop, where the ground warms it back up again. Therefore, the system concentrates the heat from the ground to provide heat for the building. Heat pumps typically provide four units of energy from one unit of electricity, making them a very efficient way of using electricity for heating.

Ground source heating pumps are used for space heating and, occasionally, pre-heating domestic hot water. More recently manufacturers have developed air source heat pumps, which use the heat energy of the air and are more suitable for those without access to a garden or field. There is another very different type of geothermal energy, which uses hot rocks in certain locations to produce hot water or steam for electricity. Although there is very limited potential for this form of geothermal energy in the UK, it is widely used in places like Iceland and the Phillipines.

Use of geothermal energy across the Highlands and Islands has been largely confined to the use of ground source heat pumps for underfloor heating in individual homes and community buildings.

Examples of this type of renewable energy system can be found at the Glenelg and Arnisdale Hall in Lochalsh, the Newvalley Housing Association and Shawbost Community Centre on the Isle of Lewis, and Orkney Housing Association’s new housing development in Kirkwall. These projects are important champions of geothermal energy, providing tangible evidence of how geothermal energy works.

Learn more about geothermal energy using our Key Links panel.

back to top >>