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photovoltaic cells used to convert sunlight into electricity, consumes silicon
and produces some waste products. In addition, large solar thermal farms can
also harm desert ecosystems if not properly managed.
Hydropower Generates Electricity
Of the renewable energy sources that generate electricity, hydropower is
the most often used. It is one of the oldest sources of energy and was used
thousands of years ago to turn a paddle wheel for purposes such as grinding
grain. Because the source of hydropower is water, hydroelectric power plants
must be located on a water source. Therefore, it wasn’t until the technology
to transmit electricity over long distances was developed that hydropower be-
came widely used.
Some people regard hydropower as the ideal fuel for electricity genera-
tion because, unlike the nonrenewable fuels used to generate electricity, it is
almost free, there are no waste products, and hydropower does not pollute the
water or the air. However, it is criticized because it does change the environ-
ment by affecting natural habitats.
Energy From Wind
Wind is simple air in motion. It is caused by the uneven heating of the
earth’s surface by the sun. Today, wind energy is mainly used to generate
electricity.
Like old fashioned windmills, today’s wind machines use blades to col-
lect the wind’s kinetic energy. With the new wind machines, there is still the
problem of what to do when the wind isn’t blowing. At those times, other
types of power plants must be used to make electricity.
Wind is a clean fuel; wind farms produce no air or water pollution be-
cause no fuel is burned.
The most serious environmental drawbacks to wind machines may be
their negative effect on wild bird populations and the visual impact on the
landscape.
Geothermal Energy
Geothermal energy is heat from within the earth. We can use the steam
and hot water produced inside the earth to heat buildings or generate electric-
ity. Geothermal power plants do not burn fuel to generate electricity, so their
emission levels are very low. They release less than 1 percent of the carbon
dioxide emissions of a fossil fuel plant. Geothermal plants use scrubber sys-
tems to clean the air of hydrogen sulfide that is naturally found in the steam
and hot water. Geothermal plants emit 97 percent less acid rain - causing sul-
fur compounds than are emitted by fossil fuel plants. After the steam and wa-
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