WHAT IS SOLAR
ENERGY?
An immense
amount of energy from the sun strikes the surface of the earth every day. This energy from
the sun is called solar energy. This energy may be captured and used for thermal
applications, or it may be converted directly to electricity to power electrical devices
using photovoltaic cells.
The sun
is a sphere of high temperature gases about 1.4 million kilometers in diameter (about
870,000 miles). The temperature of the interior of the sun is 15 million degrees Kelvin
(about 27 million deg. F). This high temperature combined with a pressure that is 70
billion times higher than atmospheric pressure on earth creates ideal conditions for
fusion reactions. The fusion reaction in the sun is hydrogen atoms combining to form
helium atoms, releasing energy in the process. This energy is in the form of high-energy
radiation, mainly gamma rays. As this radiation migrates from the center to the outside of
the solar sphere, it reacts with various elements inside the sun and is transformed into
lower-energy radiation, primarily in the visible light and heat portions of the energy
spectrum. The sun has been producing energy in this manner for around five billion years,
and will continue to do so for several more billion.
How
Energy is transformed to the Earth?
The
earth orbits the sun at a distance of 150 million kilometers (93 million miles). Radiation
expands outward from the sun at 300,000 km per second (186,000 miles per second), the
speed of light or any other type of electromagnetic radiation. The amount of time it takes
solar radiation to reach the earth is about 8 minutes
How Much Radiation Reaches Earth?
The amount of
solar energy reaching a specific location on the surface of the earth at a specific time
is called insolation, and its value depends on several factors. If the sun is directly
overhead and the sky is clear, radiation on a horizontal surface is about 1000 watts per
square meter. This is the highest value insolation can have on the earth's surface except
by concentrating sunlight with devices such as mirrors or lenses. If the sun is not
directly overhead, the solar radiation received on the surface is less due to the presence
of more atmosphere between the sun and the surface. It should be noted that insolation
decreases when a surface is not oriented perpendicular to the sun's rays. This is because
the surface presents a smaller cross-sectional area to the sun.
WHAT
WAYS CAN POEPLE UTILIZE SOLAR ENERGY?
There are several methods through which solar energy are
harnessed and here are four of them:
Flat Plate Collectors: |
A flate plate collector basically consists of an
absorber plate, a glass or plastic plate, an array of pipes and insulation. The absorber
plate is basically a plate of black-coated metal (commonly steel, aluminum or copper) used
to trap the solar radiation and turn it into heat. The transparent plate, usually
constructed of glass or plastic, is put on top of the absorber plate to preserve the heat.
Then, a series of pipes are put between the plates with cold water passing through them.
The hot water is then used to provide heating. These collectors take less space than
focusing collectors and they are comparatively cheaper although they cannot provide as
much heat. Therefore, flat plate collectors can be used in households or schools in such
applications as swimming pool heating. |
Focusing Collectors: |
There are three basic components of a
focusing collector, namely heliostats, the moveable mirrors used to track the sun for the
greatest efficiency; a parabolic collector that collects and reflects the solar energy
from the heliostats to a single centre point; and a receiver that utilizes the
concentrated energy at that centre point. A focusing collector can provide a temperature
as high as 4000 o C. The high temperature is ideal for a solar furnace that
provides contaminant-free environments for research and industrial use. Focusing
collectors can also be used to generate solar electricity. The heliostats can focus the
energy to a boiler (also known as a central receiver) that turns water into steam that
then moves a generator. |
Solar Distillation: |
The concept of solar distillation is simple.
Seawater is put in shallow ditches or tanks with two slanted transparent plates placed on
top of the roof of a house, and this water is heated and evaporated by solar energy. The
transparent plates, made of glass or plastic, collect and turn the water vapor into liquid
water as the vapor condenses. The ducts along the sides of the unit then collect the fresh
water to a main reservoir. Solar distillation is actually very similar to flat plate
collectors except that, instead of heat, distilled water is the end product. Salt is also
produced during this process, as it is the by-product of distilled seawater. |
Solar Electricity: |
There are two ways of generating electricity from
solar energy. One of them uses focusing collectors as mentioned above. The other method
uses photovoltaic cells. These cells are made up of thin pieces of semiconductors, such as
crystalline silicon and gallium arsenide. These semiconductors convert solar radiation
directly into electricity. |
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