Page 277 - Geothermal Energy Renewable Energy and The Environment

268 Geothermal Energy: Renewable Energy and the Environment

Temperatures at 6 km depth

Temp.°C

200

150
100
0

FIGUre 14.5 (See color insert following page 17.0..) Subsurface temperatures at a depth of 6 km in the
continental United States. (Courtesy of U.S. Department of Energy, Energy Efficiency and Renewable
Energy Office, Geothermal Technologies Program, Information Resources: http://www1.eere.energy.gov/
geothermal/geomap.html.)

10 8

Total annual United States energy
consumption is ~ 100 exajoules

Exajoules ( = 10 18 Joules) 10 6
7

10

10 5
0 20 40 60 80 100
Percentage of EGS resource

FIGUre 14.6 The amount of energy that would be recovered from the EGS resource base of the continental
United States, as a function of the percentage of the EGS resource that is extracted. The shaded box encloses
the region that represents 1% to 20% recovery. For reference, the amount of energy consumed by the United
States is about 100 exajoules.

also been estimated that about 1.5% of that resource could be extracted using technology that is
either currently available or is in development (Tester et al. 2006). Although that amount of extracted
energy (about 200,000 exajoules) is a small fraction of what is available, it represents more than
2000 times the amount of energy consumed by the United States in 2005.
Figure 14.6 shows the amount of energy that could be extracted, as a function of the percentage
of the total thermal resource that is available within 10 km of the surface. The shaded box rep-
resents that portion of the resource for which there is reasonable expectation that the technology
may be developed to extract that energy. Clearly, the available resource is more than sufficient to
satisfy the energy needs of the United States for centuries. A similar case can be made for the rest
of the world.