Light (particularly sunlight) can be used to create heat or generate electrical power. This is referred to as solar energy.

It is a clean form of energy production, which doesn't pollute the environment as some other forms of energy production do.

There are two forms of solar energy. The first is solar thermal conversion, which uses sunlight to create heat and then electrical power. The second is photovoltaic conversion, which uses sheets of special materials to create electricity from the sun. Photo- means "light," and voltaic means "producing electricity."

Solar Thermal Conversion

Solar thermal conversion systems use reflectors or mirrors to concentrate sunlight to extremely intense levels of heat. (Solar means "of the sun," thermal means "of heat" and conversion means "changing something from one form to another.")

You can understand this better if you consider the example of using a magnifying glass to start a fire. You may have heard of this or even tried it before. You can hold a magnifying glass under the sun, and concentrate the light on a small pile of flammable materials. The magnifying glass will make the sun's heat much stronger, and will light the materials on fire. It has been said that a magnifying glass one meter in diameter, held under the sun, will create a ray hot enough to melt stone.

If you want to experiment, hold a magnifying glass flat under the sun and put your hand under it. Very soon you will need to move your hand away - don't burn yourself.

Solar thermal conversion systems use mirrors or reflectors to concentrate sunlight onto containers full of liquid. Sometimes water is used. Sometimes other liquids are used, which retain heat better than water.

The liquids are heated up to high temperatures, and this produces steam. The steam is used to turn a turbine. The turning motion of the turbine is used to create electricity.

How does a rotating motion create electricity? When you set up a coiled wire or similar device to rotate between two magnets, it generates an electric current. This is how electric generators work, as well as windmills, nuclear power plants, and other energy plants which use such things as coal, gas, or petroleum.

Windmills use the wind to create the turning motion. Nuclear power or fossil fuels are used to heat water up, thus creating steam to turn the turbines.

Solar heating is another form of solar thermal conversion. In solar heating, an absorber is used to take in sunlight and convert it to heat. The absorber could be something simple, like black paint, or it could be a special ceramic material. A heat absorber is considered to a be good one when it collects at least 95 percent of the sun's radiation.

The absorbers are then used to heat a fluid, which is then circulated to warm up buildings or to create hot-water supplies.

Photovoltaic Conversion

As covered above, photo means "light." It comes from the Greek word phos, which means "light."

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