Page 41 - Geothermal Energy Renewable Energy and The Environment

24 Geothermal Energy: Renewable Energy and the Environment

clear, generating power from geothermal energy has consistently been pursued in regions where
volcanic activity is present. As a result, power production has been restricted to 24 countries, with
an installed capacity of 9731 MW (see Table 9.1 in Chapter 9). However, global resources far exceed
that value. It is estimated by the International Energy Agency (2006) that global capacity exceeds
150 EJ/year, which is equivalent to more than 4.5 million MW. Global power production from all
sources was estimated at 14.7 million MW. Clearly, by this estimate, geothermal power production
could contribute more than a quarter of all power production in the world.
Figures 2.7 and 2.8 show in more detail the relationship between heat flow and power generation
for the continental United States and Europe, respectively. In the case of the United States, the
western half of the continent is a region that is rich with potential geothermal resource sites, with
2
heat flow values locally exceeding 150 mW/m , reflecting the rift tectonics occurring in this region.
However, it is also clear that even within this region the variability in heat flow is high. Although the
eastern half of the country generally has low heat flow (reflecting its geologically inactive character)
2
2
in the range of 25–60 mW/m , there are regions where heat flow values exceeding 70 mW/m occur.
Some of these regions, particularly in the Gulf Coast area where oil and gas production have
occurred, are being considered for power production using binary power generation technologies
that can exploit moderate temperature resources. We will discuss these in more detail in Chapter
14 on the future of geothermal energy. Similarly, new approaches that rely on deeper drilling and
reservoir engineering, collectively described as enhanced geothermal systems (EGS; also discussed
in Chapter 14), have the potential to access significant geothermal resources that occur at depths of
6 km to 10 km even in the stable continental regions with low or moderate heat flow.

Basin and Range
Province

Canby

The
Geysers

Imperial
Valley

Gulf Coast

2
Heat flow (mW/m )
25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 150

FIGUre 2.7 (See color insert following page 17.0..) Heat flow map of the United States. (From the
Geothermal Laboratory, Southern Methodist University. With permission.)