Solar technologies use the sun's energy
to provide heat, light, hot water, electricity, and even cooling,
for homes, businesses, and industry. Despite sunlight's
significant potential for supplying energy, solar power provides
less than 1% of U.S. energy needs.
This percentage is expected
to increase with the development of new and more efficient solar
technologies.
Different types of solar collectors are used to meet different
energy needs. Passive solar building designs capture the
sun's heat to provide space heating and light. Photovoltaic
cells convert sunlight directly to electricity. Concentrating
solar power systems focus sunlight with mirrors to create a high-intensity
heat source, which then produces steam or mechanical power to run
a generator that creates electricity. Flat-plate collectors
absorb the sun's heat directly into water or other fluids
to provide hot water or space heating. And solar process
heating and cooling systems use specialized solar collectors and
chemical processes to meet large-scale hot water and heating and
cooling needs.
Solar technologies produce few negative environmental impacts
during collector operation. However, there are environmental
concerns associated with the production of collectors and storage
devices. In addition, cost is a great drawback to solar
power. Although sunlight is free, solar cells and the equipment
needed to convert their direct-current output to alternating current
for use in a house is expensive. Electricity generated by
solar cells is still more than twice as expensive as electricity
from fossil fuels. Part of the problem with cost is that
solar cells can
only operate during daylight hours. In contrast,
a coal or natural gas plant can run around the clock, which means
the cost for building the plant can be spread over many more hours
of use.
Around the United States, available sunlight varies considerably
as a result of differences in cloud cover and latitude, and also
varies with the seasons. In the summer, longer daylight hours and
a higher sun angle provide more solar power, compared to the winter
when the sun is up for fewer hours and at a lower position in the
sky. These variations must be taken into consideration when planning
solar collection
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