Thursday, 1 December 2011

Source of Energy- Solar Energy

Picture of sun
Plants use the sun's light to make food. 
Animals eat plants for food. Decaying plants hundreds of millions of years ago produced the coal, oil and natural gas that we use today. So, fossil fuels is actually sunlight stored millions and millions of years ago.
Indirectly, the sun or other stars are responsible for ALL our energy. Even nuclear energy comes from a star because the uranium atoms used in nuclear energy were created in the fury of a nova – a star exploding.
Let's look at ways in which we can use the sun's energy.

Solar Hot Water
Today, solar water heaters are making a comeback. They heat water for use inside homes and businesses. They also heat swimming pools like in the picture.
Panels on the roof of a building, like this one on the right, contain water pipes. When the sun hits the panels and the pipes, the sunlight warms them.
That warmed water can then be used in a swimming pool.

Solar Thermal Electricity
Solar energy can also be used to make electricity.
Some solar power plants, like the one in the picture to the right in California's Mojave Desert, use a highly curved mirror called a parabolic trough to focus the sunlight on a pipe running down a central point above the curve of the mirror. The mirror focuses the sunlight to strike the pipe, and it gets so hot that it can boil water into steam. That steam can then be used to turn a turbine to make electricity.

Solar Cell
graphic depicting simple PV cell
We can also change the sunlight directly to electricity using solar cells.
Solar cells are also called photovoltaic cells – or PV cells for short – and can be found on many small appliances, like calculators, and even on spacecraft. They were first developed in the 1950s for use on U.S. space satellites. They are made of silicon, a special type of melted sand.
When sunlight strikes the solar cell, electrons (red circles) are knocked loose.They move toward the treated front surface (dark blue color). An electron imbalance is created between the front and back. When the two surfaces are joined by a connector, like a wire, a current of electricity occurs between the negative and positive sides.

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