What are the best energy sources? "Best" depends
on many factors - how the energy is being used, where
it is being used, what energy sources are available,
which sources are most convenient and reliable, which
5 are easiest to use, what each costs, and the effects on
public safety, health, and the environment. Making smart
energy choices means understanding resources and their
relative costs and benefits.
Some energy sources have advantages for specific
10 uses or locations. For example, fuels from petroleum
are well suited for transportation because they pack a
lot of energy in a small space and are easily transported
and stored. Small hydroelectric installations are a good
solution for supplying power or mechanical energy close
15 to where it is used. Coal is widely used for power
generation in many fast-developing countries - including
China, India, and many others - because domestic
supplies are readily available.
Efficiency is an important factor in energy costs.
20 How efficiently can the energy be produced, delivered,
and used? How much energy value is lost in that process,
and how much ends up being transformed into useful
work? Industries that produce or use energy continually
look for ways to improve efficiency, since this is a key to
25 making their products morecompetitive.
The ideal energy source - cheap, plentiful, and
pollution-free - may prove unattainable in our lifetime,
but that is the ultimate goal. The energy industry is
continuing to improve its technologies and practices, to
30 produce and use energy more efficiently and cleanly.
Energy resources are often categorized as
renewable or nonrenewable.
Renewable energy resources are those that can be
replenished quickly - examples are solar power,
35 biomass, geothermal, hydroelectric, wind power, and
fast-reaction nuclear power. They supply about seven
percent of energy needs in the United States; theother
93 percent comes from nonrenewables. The two largest
categories of renewable energy now in use in the U.S.
40 are biomass - primarily wood wastes that are used by
the forest products industry to generate electricity and
heat - and hydroelectricity.
Nonrenewable energy resources include coal, oil,
natural gas, and uranium-235, which is used to fuel
45 slow-reaction nuclear power. Projections of how long a
nonrenewable energy resource will last depend on many
changeable factors. These include the growth rate of
consumption, and estimates of how much of the remaining
resources can be economically recovered. New exploration
50 and production technologies often increase theability of
producers to locate and recover resources. World
reserves of fossil energy are projected to last for many
more decades - and, in the case of coal, for centuries.
In: http://www.classroom-energy.org/teachers/energy_tour/pg5.html
Gabarite Concurso