Energy and Human Ambitions on a Finite Planet, 2021a

16 Small Players 279
The most common scheme—labeled “hydrothermal”—is to drill two
holes into the ground near each other, injecting water into one <strong>and</strong>
collecting pressurized steam from the other. Fractures in the rock permit
water <strong>and</strong>/or steam to flow between the two holes. Alternatively, but
far less common, a fluid 13 can be run through a closed loop that passes
through the hot medium. By either direct use of the steam in the
hydrothermal case, or generating steam from the hot fluid in the closedloop
case, the resulting steam can be used to run a turbine <strong>and</strong> generator
in the usual way.
13: ...notnecessarily water now
A newer form, called “binary” geothermal uses two fluids: water in the
ground as in other schemes, but a second fluid having a much lower
boiling point to make a steam analog at lower temperatures. This opens
additional power generation possibilities at temperatures below 100 ◦ C,
but of course will suffer the inevitable efficiency hit when T h is lower,
according to Eq. 16.1.
Globally, roughly 10 GW of electricity is produced from geothermal
energy [107], <strong>and</strong> an estimated additional 28 GW of direct heating is
obtained from this source [108]. Together, these account for 0.4% of the
18 TW global energy budget, after a thermal equivalent adjustment.
Country GW installed GW produced % elec.
U.S. 3.5 1.9 0.4
Philippines 1.9 1.3 27
Indonesia 1.5 1.2 4
New Zeal<strong>and</strong> 1.0 0.85 15
Mexico 1.0 0.7 3
Italy 0.9 0.7 1.5
Icel<strong>and</strong> 0.7 0.6 30
World Total 12.6 9.4 0.4
[107]: Intern’l Renewable <strong>Energy</strong> Agency
(2018), Renewable <strong>Energy</strong> Statistics 2018
[108]: (2020), Geothermal Heating
Table 16.2: Global geothermal electricity
production in 2016 [85, 107, 109]. Note that
the percentage is the fraction of electricity,
not total energy, contributed by geothermal.
The capacity factor tends to be relatively
high for this non-intermittent resource (see
Problem 6).
Table 16.2 lists the top 7 producers of geothermal electricity, capturing
72% of the global total. Note that many are on the Pacific Rim, sometimes
called the “ring of fire” for its volcanic activity. Icel<strong>and</strong> gets 30% of its
electricity 14 from geothermal sources. But in absolute terms, it is a small
amount of energy. Considering that a single nuclear plant puts out about
1 GW, the countries in Table 16.2 have the equivalent of 1–2 nuclear
plants in the form of geothermal (compare to Table 15.8; p. 256).
14: And electricity is only about one third
of Icel<strong>and</strong>’s energy dem<strong>and</strong>.
The U.S. gets an average of 1.9 GW of electrical production 15 from geothermal
sources [85]. 72% of this is produced in California—almost all at a [85]: U.S. <strong>Energy</strong> Inform. Admin. (2020),
15: . . . ∼0.4% of total electricity
site called The Geysers in the northern part of the state—accounting for Electric power monthly
∼6% of the state’s electricity. Another 22% of U.S. geothermal electricity
is produced in in Nevada. The rest is in Utah, Hawaii, Oregon, Idaho,
<strong>and</strong> New Mexico, in that order (7 states total).
Geothermal is just a small player. The fact that a country like Icel<strong>and</strong>
can produce a large fraction of its electricity this way mostly tells us that
Icel<strong>and</strong> is on a geological hot-spot <strong>and</strong> is not very populated. We should
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.