HARNESSING THE POWER OF THE SUN
TO PRODUCE POWER THROUGH SOLAR ENERGY
Solar power describes a number of
methods of harnessing energy from the light of the sun. It is already
in widespread use where other supplies of power are absent such as in
remote locations and in space. As the earth orbits the sun, it
receives approximately 1,020 W/m2 at sea level.
Solar power may be classified as direct
and indirect. Direct solar power involves only one transformation
into a usable form, for example, sunlight hits a photovoltaic cell to
create electricity and warms the surface or heats the water when the
light is converted to heat by interacting with matter.
Indirect solar power involves more than
one transformation to reach a usable form. Many other types of power
generation are indirectly solar-powered, for example,
(i) vegetation use photosynthesis to
convert solar energy to chemical energy, which can later be burned as
fuel to generate electricity;
(ii) energy obtained from oil, coal,
and peat originated as solar energy captured by vegetation in the
remote geological past and fossilised;
(iii) hydroelectric dams and wind
turbines are indirectly powered by solar energy through its
interaction with the earth’s atmosphere and the resulting weather
phenomena;
(iv) energy obtained from methane
(natural gas) may be derived from solar energy either as a biofuel or
fossil fuel; (v) ocean thermal energy production uses the thermal and
gradients that are present across ocean depths to generate power.
Solar power can also be classified as
passive or active. Passive solar systems are systems that do not
involve the input of any other forms of energy apart from the
incoming sunlight. Active solar systems are those that use additional
mechanisms such as circulation pumps, air blowers, or automatic
systems that aim collectors at the sun.
Effective use of solar radiation often
requires the radiation (light) to be focused to give a higher
intensity beam, that is, parabolic dish, parabolic trough, etc., are
used to concentrate light at a point or a line. At the focus,
high-concentration photovoltaic cells (solar cells) or a thermal
energy “receiver” may be placed.
Most of the solar energy used today is
harnessed as heat or electricity. Solar design aims the use of
architectural features to replace the use of grid electricity and
fossil fuels with the use of solar energy and decrease the energy
needed in a home or building with insulation and efficient lighting
and appliances.
Following are the main applications of
solar energy:
Photovoltaic systems: Solar
cells, also known as photovoltaic cells, use the photovoltaic effect
of semiconductors to generate electricity directly from the sunlight.
Because of high manufacturing costs, their use has been in limited
until recently.
One cost-effective use has been in very
low power devices such as calculators with LCDs. Another use has been
in remote applications such as roadside emergency telephones, remote
sensing, cathodic protection of pipelines, and limited to isolated
home power applications.
A third use has been to power orbiting
satellites and other spacecraft. However, the continual decline of
manufacturing costs (dropping at 3% to 5% a year in recent years) is
expanding the range of cost effective uses.
Solar heating: Solar hot water
systems are quite common in some countries where a small flat panel
collector is mounted on the roof and is able to meet most of a
household’s hot water needs. Cheaper flat panel collectors are also
often used to heat swimming pools, thereby extending the swimming
season. There are some new applications of thermal hot water, like
air cooling, currently under development.
Solar cooker: Taps the sun’s
power in an insulated box, which has been successfully used for
cooking. Solar cooking is helping many developing countries both by
reducing the demands for local firewood and maintaining a cleaner
environment for the cooks.
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