Energy from the Sun
Each day more solar energy hits the Earth than the total
energy that the 5.9 billion inhabitants of the planet would
consume in 27 years. Clean energy from the sun can replace
power sources that pollute the environment. The few
emissions of greenhouse gases or air pollutants generated by
solar energy technologies occur mostly during the
manufacturing process. A 100-megawatt solar thermal electric
power plant, over its 20-year life, will avoid more than
3 million tons of carbon dioxide (CO2) emissions when
compared with the cleanest conventional fossil fuel-powered
electric plants available today.
Solar energy technologies are divided into two major kinds:
photovoltaic (PV) cells and modules, which convert sunlight
directly into electricity; and solar thermal technologies, which
collect solar heat energy for direct heating of space and water
and indirect production of electricity. Photovoltaic devices,
first used in the space program, generate electricity to power
residences, satellites, highway signs, communication stations,
navigation buoys, streetlights, calculators, and more. Building-
integrated solar products such as solar roof shingles and
opaque glass PV façades also are now available on the market.
In the last seven years, worldwide photovoltaic sales have
nearly tripled.
Photovoltaic arrays can be combined to create large-scale
PV power plants. The Sacramento Municipal Utility District in
California operates a 1,600-module, 2 megawatt photovoltaic
power plant that produces enough electricity to serve 660
homes in the Sacramento area.
Solar thermal power is the least costly form of solar electricity
for grid-connected applications today. Concentrating solar power
technologies—parabolic troughs, power towers, and dish/engine
systems—convert sunlight into electricity efficiently and with
minimum effect on the environment.
Other uses of thermal energy from the sun include solar
water heating for buildings and swimming pools, and solar
space heating and cooling systems for buildings.
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