Environmental Engineering Reference
Figure 2.4 Proportions (%) of U.S. energy consumption supplied by primary energy sources, 1996. (Data
from U.S. Department of Energy, Energy Information Agency, 1997. Monthly Energy Review, April 1997.)
and geothermal and other renewables 0.4%. These proportions are not greatly different from those
of the world as a whole. In 1996, about 50.5% of the U.S. petroleum and 12% of natural gas
consumption was supplied by foreign sources.
GLOBAL ELECTRICITY CONSUMPTION
Electricity is a secondary form of energy, because primary energy (fossil, nuclear, hydropower,
geothermal, and other renewable sources of energy) is necessary to generate it. The trend of the
world's electricity production from 1990 to 1997 and the prediction to 2020 is depicted in Figure 2.5.
In 1997, the world's total electricity production was close to 12 trillion kilowatt hours. By 2020,
the production is predicted to increase to over 21 trillion kWh.
Of the 1997 electricity production, 63% was from fossil energy, 19% was from hydroenergy,
17% was from nuclear energy, and less than 1% was from geothermal and other renewable sources
(see Figure 2.6). Because the worldwide thermal efficiency of power plants is about 33.3%, in 1997
these plants consumed about 32.6% of the world's primary energy and about 55.5% of the world's
fossil energy. The majority of the latter (over 80%) was in the form of coal. In the United States,
Europe, Japan, and some other countries, in the past decades, natural gas became a preferred fuel
for electricity generation, and many new power plants were built that employ the method of Gas
Turbine Combined Cycle (GTCC), which is described in Section 5.3.1.
The reliance on energy sources for electricity production varies from country to country. For
example, in the 1996, U.S. electricity production amounted to 3079 billion kWh. Of this, coal
contributed 56.4%, nuclear power plants 21.9%, hydroelectric power plants 10.7%, natural gas
8.6%, petroleum 2.2%, and geothermal and other sources less than 0.3% (see Figure 2.7).
Hydropower is a significant contributor to electricity generation in many countries. For exam-
ple, in Norway practically all electricity is produced by hydropower, in Brazil 93.5%, New Zealand
74%, Austria 70%, and Switzerland 61%. China and India produce about 19% of their electricity
from hydropower. While hydroelectricity is a relatively clean source of energy and there is still a
potential for its greater use worldwide, most of the accessible and high “head” hydrostatic dams
are already in place. Building dams in remote, inhospitable areas will be expensive and hazardous.
Furthermore, there is a growing public opposition to damming up more rivers and streams for