Geothermal Energy Facts
The relatively constant temperature of the top 15 metres of the Earth's surface, however, is much cooler – for every 100 metres you go below ground, the temperature increases by about 3°C. This energy can be tapped and used to heat or cool buildings.
A heat pump uses a series of pipes to circulate fluid through the warm ground.
In the winter when the ground is warmer than the buildings above, the liquid absorbs heat from the ground, which is then concentrated by means of heat exchangers or collectors, and transferred to the buildings.
In the summer, when the ground is cooler, the pump transfers heat from the buildings back into the ground, or cools an air conditioning system.
Harnessing geothermal energy often requires digging boreholes to great depths.In volcanic regions, thermal groundwater is available that can be used directly through hydrothermal power plants, a mature technology, to generate electricity and heat.
Otherwise, where such hot water is not available, water can be pumped between hot layers of rock and then brought back to the surface at high temperature by means of a second borehole.
This new technology, called Enhanced Geothermal Systems or "hot rock"’ technology, uses high heat producing rocks typically found between 3-5km below the surface of the Earth.
A growing industry
With the exception of the Iceland, the US, the Philippines, Indonesia, New Zealand, Mexico and Italy, the use of deep geothermal energy in power plants is still at its infancy.
Further research and development are required to reduce costs and optimize technology.
WWF's Energy Report anticipates that by 2050 geothermal energy could account for around 58 million megawatt hours of electricity per year.
The IPCC projects 24 GW installed by 2020 and 140 GW by 2050.
The challenge will be to tap the huge electricity potentials that lie under the ground, for example in the African Rift Valley or around the geothermal Ring of Fire in Southeast Asia and the Pacific, as well as to systematically heat and cool buildings with shallow geothermal technology.
The electricity produced is also more available, as fossil-fuelled power plants produce electricity 65-75% of the time compared to 90% from geothermal power plants.
While geothermal resources are not spread uniformly, geothermal heat pumps can be used almost anywhere. When a heat pump is used to provide domestic heating, the savings on electricity alone can outweigh the cost of installing and running the system.
Where geothermal energy is used in agriculture, such as to heat greenhouses, heating costs can be cut by up to 80%.