The earth’s crust contains a virtually limitless amount of thermal energy which is being continuously replenished by heat conduction from the mantle and core below it. As a result, the temperature in the rocks beneath our feet increases with depth at an average rate of about 25ºC per km, which means very useful temperatures can be reached with conventional drilling technology.

In volcanic areas and at some tectonic plate boundaries the temperature gradient is much higher and temperatures of several hundred degrees can be found within 2km of the surface. Where these temperatures coincide 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 or the supply of heat.

Geothermal energy has been commercially harnessed in this way for decades and today 90 countries use it to generate electricity or supply renewable heat. It is a clean, sustainable, low carbon source of energy able to provide power, heat and cooling.

In recent years researchers and developers have been looking for ways to bring the benefits of geothermal energy to countries away from the established geothermal regions by exploring for deeper reservoirs and enhancing the natural conditions in so-called Engineered Geothermal Systems (EGS) and by improving the technology to allow efficient use of lower temperature resources.