GEOTHERMAL

The Heat Beneath Your Feet Geothermal energy, the heat beneath your feet, is the most stable renewable energy source. Three feet below most of the eartth's surface, the ground temperature is always at least a mild 50 degrees F., and this temperature increases with depth to several hundred degrees.

This heat can be used in many ways. One of the easiest ways to take advantage of this warmth is to build earth-sheltered and underground buildings. Protected from exposure to cold air and winds, a well-designed earth-sheltered house can save much of the energy that standard houses use. The Underground Space Center office building in Minneapolis, Minnesota was constructed for less money than a normal building of the same size, yet most of the structure is below the ground.

Large scale applications of geothermal power are possible at sites with large reserves of underground hot water, hot rock, or steam. Eighty countries have such underground heat reservoirs. For example, most of the buildings in cold Reykjavik, Iceland are heated with geothermal water. Year-round gardening is possible, and the city is very clean due to the resulting minimal use of fossil fuels, like coal and oil. Similarly, Boise Idaho has used hot springs for home heating since the 1890's, and France, Hungary, and New Zealand use underground hot water for domestic and industrial purposes.

Currently, at least eight countries generate geothermal electricity. The Italians built the first such plant in 1904, with a power output of 350 million watts. The world's largest plant, at the Geysers in California, generates enough electricity to power San Francisco. A 1975 study by the US Geological Survey estimates that known geothermal resources in the US could produce 140,000 watts of electricity over the next 30 years, or about the same power as 140 nuclear plants.

Geothermal energy is a vast non-polluting source of heat and electricity. Much of the technology is already known and its further development will play an important role in the transition to a renewable energy future.