What is geothermal energy?
In the global push to end reliance on fossil fuels, green energy sources like solar and wind power have gotten lots of attention. But geothermal energy is another environmentally friendly energy source. It’s the underground heat left over from the molten rocks that formed Earth billions of years ago, and it can be tapped to heat buildings and generate electricity.
“The Earth is a heat engine,” says William Glassley, an earth scientist at the University of California, Davis, and an expert in geothermal energy. “At depths of 20 miles or more, anywhere on the planet, there is enough heat constantly available to generate sufficient power to supply the entire world.”
Glassley says geothermal power will grow in importance in coming years, as new techniques for finding, tapping and exploiting geothermal energy are developed.
Geothermal energy is present even below the coldest parts of Earth’s surface — if you dig deep enough. In most places, Earth’s heat is trapped at depths of more than 20 miles. But in so-called geological hotspots, geothermal energy is near the surface — and is apparent in geysers, hot springs and volcanic eruptions.
People have exploited geothermal energy for tens of thousands of years, using it to cook and bathe, for example. During the Roman Empire, about 2,000 years ago, hot springs were used for public baths and underfloor heating — as in the famous spa town of Bath, England.
Today, geothermal energy tapped via holes drilled in the ground is used to heat and cool houses and other buildings. The underground environment functions as a sort of heat reservoir, with heat being drawn up into a building during cold weather and excess heat being dumped underground to lower indoor temperatures during hot weather.
The cost of a geothermal heat pump system varies according to the climate and other factors. A typical residential system might be twice that of a conventional heating and cooling system, but geothermal heating and cooling systems can cut utility costs by up to 60 percent.
Geothermal heat is also used in certain industrial and agricultural processes — for example, to dry lumber and crops.