Geoscience Reference
In-Depth Information
(a)
(b)
Figure 13.5.
(a) Steam from geothermal hot water in a natural river, Hveragerdi, Iceland, May 1, 2010.
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Svobodapavel/Dreamstime.com. (b) Geothermal power station in Iceland, October 6, 2007.
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Steve Allen/Dreamstime.com.
up a borehole is kept in an enclosed pipe and heats a low-
boiling-point organic fluid, such as isobutene or isopen-
tane, through a heat exchanger. The evaporated organic
turns a turbine that powers a generator, producing elec-
tricity. Because the water from the reservoir stays in an
enclosed pipe when it passes through the power plant
and is reinjected to the reservoir, binary systems pro-
duce virtually no emissions of CO
2
(g), NO(g), SO
2
(g),
or H
2
S(g). About 15 percent of geothermal plants today
are binary plants.
13.2.4. Hydroelectric
Water can generate electricity when it drops gravita-
tionally, driving a turbine and generator. Although most
hydroelectric power
is produced by water falling from
areservoir behind a large dam (
large hydroelectric-
ity
;Figure 13.6a), some is produced by water flowing
from a river directly through a pipe or tunnel, past a
turbine, and back to the river (Figure 13.6b). The lat-
ter is referred to as
run-of-the-river hydroelectricity
.
(a)
(b)
Figure 13.6.
(a) Three Gorges Dam, China, on July 31, 2010, with air pollution in the background. Construction
began in 1994 and was completed in 2009. It is 2.335 km long, 185 m high, 18 m wide at the top, and 130 m
wide at the bottom.
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Jjspring/Dreamstime.com. (b) Run-of-the-river hydroelectric plant, January 30, 2011.
Paura/Dreamstime.com.
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