Page 595 - Environment: The Science Behind the Stories

Intake Direction of Hydropower’s expansion
river flow
Penstock is limited
Today the world is witnessing some gar-
gantuan hydroelectric projects. China’s
recently completed Three Gorges Dam (pp.
421–422) is the world’s largest. Its reser-
voir displaced 1.3 million people, and the
dam is now generating as much electricity
as dozens of coal-fired or nuclear plants.
However, hydropower has less poten-
tial for expansion than some other renewa-
ble energy sources. The main reason is that,
as in Sweden, most of the world’s large riv-
ers that offer excellent opportunities for
hydropower are already dammed. In addi-
Powerhouse tion, as people have grown more aware of
Generator the ecological impacts of dams, residents
Turbine in some regions are resisting dam construc-
Tailrace tion. Indeed, in Sweden, hydropower’s
contribution to the national energy budget
has remained virtually unchanged for 40
years. In the United States, 98% of rivers
FIGURE 20.25 Run-of-river systems divert a portion of a appropriate for dam construction already are dammed, many
river’s water. Water may be piped downhill through a powerhouse
and released downriver, as shown. Other designs use water as it of the remaining 2% are protected under the Wild and Scenic
flows over shallow dams. Rivers Act, and many people now want to dismantle some dams
and restore river habitats (p. 422).
Overall, hydropower will likely continue to increase in
The great age of dam building for hydroelectric power (as developing nations that have yet to dam their rivers, but in
well as for flood control and irrigation) began in the 1930s in the developed nations hydropower growth may slow down. The
United States, when the federal government constructed dams International Energy Agency forecasts that hydropower’s
as public projects, partly to employ people and help end the share of electricity generation will decline very slightly
economic depression of the time. U.S. dam construction peaked between now and 2035, whereas the share of other renewable
in 1960, when 3123 dams were completed in a single year. energy sources will nearly triple. Newer renewable energy
American engineers subsequently exported their dam-building sources have potential for rapid growth (Chapter 21).
technologies, notably to nations of the developing world. In
India, Prime Minister Jawaharlal Nehru commented in 1963 that
“dams are the temples of modern India,” referring to their central
importance in the development of energy capacity in that nation. Conclusion
Given limited supplies of fossil fuels and their considerable
TABLE 20.4 Top Producers of Hydropower environmental impacts, many nations have sought to diversify
HYDROPOWER PERCENTAGE OF their energy portfolios with alternative energy sources. The
PRODUCED NATION’S ELECTRIC- three most developed and widely used alternatives so far are
(Percentage of ITY GENERATION nuclear power, bioenergy, and hydropower.
NATION world total) FROM HYDROPOWER Nuclear power showed promise at the outset to be
China 20.5 17.2 a pollution-free and highly efficient form of energy. But
escalating costs and public fears over safety in the wake
Brazil 11.5 78.2
of accidents at Three Mile Island, Chernobyl, and Fuku-
Canada 10.0 57.8
shima stalled its growth, and a few nations are attempting
United States 8.1 6.5 to phase it out completely. Bioenergy sources are diverse
Russia 4.8 16.2 and range from traditional fuelwood to newer biofuels and
Norway 3.4 94.7 various means of generating biopower. These sources can
India 3.3 11.9 be carbon-neutral but are not all strictly renewable. Hydro-
power is a renewable, pollution-free alternative, but it can
Japan 2.6 8.1
expand only so much further and also involves substantial
Venezuela 2.2 64.9
ecological impacts. Some nations, such as Sweden, already
France 1.9 11.7 rely heavily on these three conventional alternatives, but it
Rest of world 31.7 15.4 appears that our global society will need further renewable
594 Data from the International Energy Agency. sources of energy as well.

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