What is geothermal electricity?

Geo, meaning earth, and thermal, meaning heat, is a naturally occurring energy in the form of heat under the surface of the earth.  This energy source can be only a few hundred metres below the surface in water that comes to the surface of the ground or in hot rocks thousands of metres below the surface. This energy originates deep within the earth's crust.

Normally, the temperature increases approximately 3^oC per 100 metres as we go down beneath the Earth's surface.  This is called a "natural geothermal gradient".  Close to volcanoes or where the Earth's crust is thin (for example, in New Zealand's North Island), the geothermal gradient can be much higher.

Geothermal energy is a clean, renewable resource that has a huge potential to meet the world's energy requirements. Geothermal power capacity is estimated to be 50,000 times the energy of all known petroleum reserves. It is considered a renewable resource because the heat emanating from the interior of the Earth is essentially limitless.

Geothermal energy is used for:

• Electricity production (9,000 MW installed worldwide);
• Direct use purposes such as district heating in France, Germany and Iceland; and
• Home heating on a smaller scale through geothermal heat pumps.

The USA, Philippines, New Zealand and Iceland are amongst the world's largest generators of geothermal energy.

Over the past five years, there has been rapidly increasing global interest in geothermal generation as a source of clean electricity.  Geothermal generation emits from zero to 10% of the CO² emissions of a coal fired power station.

The world readily embraces new clean energy sources.  For example, we have seen rapid growth in wind generation and coal seam gas production over the past decade.  Geothermal electricity generation is now poised to grow rapidly too. 

Hot Rock is targeting sedimentary geothermal and volcanic geothermal systems for development.