Geothermal power is electricity generated from heat extracted from the earth. Geothermal power is possible in locations with volcanoes, hot springs, or magma hot spots. This amounts to regions with tectonic activity, such as the Pacific rim, Africa's Great Rift Valley, and Iceland.
Geothermal power can also be used directly for heating. Hot springs and thermal vents have heated baths and homes since ancient times. For example, the springs at Bath, England, have been in use since Roman times. This is a conceptually simple process, possibly after drilling to gain access to hot water. Underground water is pumped out and used to heat steam pipes. These pipes run to spas, greenhouses, local residences, and the like.
Geothermal electrical generation, by contrast, is only about 50 years old. The power source is underground steam or hot water under pressure that expands to form steam. Steam turbines then run generators. The efficiency of this process depends on the temperature of the input. Because underground steam is at a much lower temperature than, say, burning coal in a coal power plant, geothermal power is much less efficient. The operating costs are much lower, however.
Advantages and Disadvantages
Geothermal power has the advantage of being consistent, unlike other alternative sources such as solar and wind. Operating costs are low, as mentioned, although the initial exploration and drilling may be expensive.
In the way of disadvantages, pollution considerations are small but not zero – underground water may contain sulfur and other undesirable trace elements. These elements must be scrubbed from the steam or hot water before it is disposed of. Extraction of underground water can cause land to settle and can trigger minor quakes.
Because of the limited geographic availability, low efficiency, and other factors, geothermal electrical generation accounts for less than 1% of the world's power use.