Environmental Engineering Reference
In-Depth Information
7
CHAPTER
Renewable Energy
7.1
INTRODUCTION
Renewable energy systems draw energy from the ambient environment rather than from the con-
sumption of mineral fuels (coal, oil, gas, and nuclear). The ultimate source of most renewable
energy production is the sun, whose total radiant energy flux intercepted by the earth provides a
much greater source of power than can be captured by practical renewable energy schemes.
1
De-
spite the vast amounts of energy that are potentially available from renewable sources, collecting
and utilizing that energy in an economical and effective manner is far from an easy task.
There are many reasons for the growth of interest in renewable energy systems. Such systems
are independent of fuel supply and price variabilities and are thereby economically less risky.
Renewable energy resources are more uniformly distributed geographically than are fossil fuels,
providing indigenous energy resources for most fuel-poor nations. Some forms of renewable en-
ergy operate efficiently in small units and may be located close to consumers, reducing energy
transmission costs. In the United States in recent years, governmental regulation of the electric
utility system has provided some economic incentive for the construction of renewable energy
systems as a small part of the mix of electric power sources. Because renewable energy sources
have lesser environmental effects than conventional energy sources, especially in regard to the
emission of toxic and greenhouse gases to the atmosphere, they are expected to become an im-
portant source of energy in future years as environmental controls become more stringent. But
the major obstacle to greater use of renewable energy is its generally higher cost compared to
conventional sources.
The renewable technologies that currently are employed or show promise of becoming practical
are: (a) hydropower, (b) biomass power, (c) geothermal power, (d) wind power, (e) solar heating and
thermal electric power, (f ) photovoltaic power, (g) ocean tidal power, (h) ocean wave power, and (i)
ocean thermal electric power. As shown in Figures 2.2 and 2.4, renewable energy accounts for 4.4
% of total U.S. 1996 energy production and 8.2% of world energy production in 1997, almost all
of it in the form of hydropower, but the amount of non-hydro renewable power is growing rapidly.
Some renewable energy systems produce only electrical power, which has a higher economic
value than heat. Among these are hydro, wind, photovoltaic, tidal, and ocean wave power. Never-
theless, biomass, geothermal, and solar systems, which can deliver both electric power and heat, are
equally important renewable energy sources. Table 7.1 lists the 1997 U.S. renewable energy pro-
1
Exceptions are tidal power, which derives its energy from the gravitational energy of the earth-moon-sun
system, and geothermal power, whose source is nuclear reactions in the earth's interior.
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