Environmental Engineering Reference
In-Depth Information
refrigerator. It can also be run in reverse to supply
cooling. These units are reliable and cost-effective. Their
contribution to reducing emissions is small today but is
growing rapidly.
.
Hydropower
The contribution of hydroelectric power systems in
to world renewable energy was over
gigawatts
averaged over the year (GWa), up by over
% from what
,
it was when the
first edition was written in
dwar
ng all but biomass. In the United States, hydro-
power amounted to over
% of the electricity from all
renewables. Worldwide, almost all of this comes from
large power dams like the Columbia River dams in the
United States, the Aswan dam on the Nile River in Egypt,
or the Three Gorges Dam on the Yangtze River in China.
Large power dams have potential environmental prob-
lems of their own, and a balance will have to be struck
between those concerns, concerns about global warming,
and the need for affordable energy. In the developing
world the need for energy is dominant.
Big power dams store water as well as generating elec-
tricity and more of that will be needed as temperatures
rise. For example, California gets much of its water in the
summer from melting snow in its mountains. As tempera-
tures rise, there will be less snow and more rain with more
runoff in the winter, meaning less water in the summer
River
flow varies over the year so hydropower is generally given as a
yearly average. The capacities of the plants are typically about twice the
average output.
