Environmental Engineering Reference
In-Depth Information
Geothermal heat is inexhaustible and releases no greenhouse gases or
radiation. The many tens of thousands of holes drilled in the United
States in search of oil and natural gas have revealed the variation in depth
temperature over the United States (fi gure 7.3). The data show possibili-
ties for harnessing the earth's heat directly almost everywhere in the
country. In many places in the West, it is suitably hot at depths of only
a few hundred feet, but in mid-America, suffi ciently high geothermal
temperatures occur only at depths of 10,000 to 20,000 feet. In the East,
suitable temperatures are present only at even greater depths, and it is
not clear that this deep heat can be tapped into economically. However,
Google in 2008 invested $11 million in new deep drilling technology
that can drill through hard rock fi ve times faster than current methods.
If this development succeeds, geothermal power will be practical almost
anywhere.
Figure 7.3
Temperatures in the forty-eight contiguous states at a depth of 20,000 feet. In some western
areas, temperatures exceed 300°F. Although Hawaii and Alaska are not shown on the map,
Hawaii has active volcanoes, as does coastal Alaska, indicating both states have geothermal
resources at shallow depths. (Department of Energy) 2004
