Renewable Energy Summary

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					Several sustainable energy sources could reduce or eliminate our
dependence on fossil fuels and nuclear energy. Some of these sources have
been used for centuries but have been neglected since fossil fuel cam
into widespread use. Passive solar heat, fuel wood, windmills, and water
wheels, for instance, once supplied a major part of the external energy
for human activities. With increased concern about the dangers and costs
associated with conventional commercial energy, these ancient energy
sources are being reexamined as part of a more sustainable future for
humankind.Exciting new technologies have been invented to use renewable
energy sources. Active solar air, and water heating, for instance,
require less material and function more quickly than passive solar
collection. Wind is now the cheapest form of new energy in many places.
It has potential to supply one third or more of our energy requirement.
Parabolic mirrors can produce temperatures high enough to be used as
process heat in manufacturing.Fuel cells use catalysts and semi permeable
electrolytes to extract energy from fuels such as hydrogen or methanol at
high efficiency and with very low emissions. Ocean thermal electric
conversion, tidal and wave power stations, and geothermal steam sources
can produce useful amounts of energy in some localities. One of the most
promising technologies is direct electricity generation by photovoltaic
cells. Since solar energy is available everywhere, photovoltaic
collectors could provide clean, inexpensive, nonpolluting, renewable
energy independent of central power grid or fuel supply system.Biomass
also may have some modern application. In addition to direct combustion,
biomass can be converted into methane or ethanol, which are clean
burning, easily storable, and transportable fuels. These alternative uses
of biomass also allow nutrients to be returned to the soil and help
reduce our reliance on expensive, energy consuming artificial fertilizer.

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