Geothermal Energy
One of the few energy sources that is not derived from solar energy is Geothermal power. This energy is stored as heat in the rocks within the earth. We sometimes see this heat in the form of molten lava from areas of volcanic activity.
Geothermal energy is not strictly a renewable energy source, but it can be classified as one because the underground rocks continue to heat up again once the heat has been extracted.
Extracting geothermal heat
The heat is usually extracted by pumping water down through the hot rock strata and using the hot water (or steam) that is returned to generate electricity or for district heating systems.
As of 2007, geothermal power was used to supply 10GW of electricity, approximately 0.3% of the global demand for electricity.
Krafla Geothermal Station
User: Asgegg
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Nesjavellir Geothermal Power Plant
User: Asgegg
image in public domain
Ohaaki geothermal power station
User: SmokySteve
image in public domain
Geothermal power world wide
The United States has the largest geothermal power plants in the world, in a site in California. Countries that generate a significant share of their electricity from geothermal sources include the Philippines and Iceland.
How a Geothermal Plant Works