An Energy That Never Run Out.

A source of energy more powerful than a million electric power plants. And imagine that this energy source will never run out, at least not for a few billion years. This energy source is not imaginary. It�s the Sun. Solar energy shines down on us every day.

Solar energy is produced inside the Sun. It is the source of nearly all energy on Earth. This energy is stored in the ground, the oceans, and the wind. Even fossil fuels, such as oil and natural gas, come from ancient plant life that once soaked up sunlight. Today we use solar energy to heat buildings and produce electricity.

You may have seen solar collecting plates on top of buildings. They are thin, flat boxes. The solar collectors capture the Sun�s energy. Sunlight heats air or water flowing through tubes in the boxes. The tubes carry the heat into the building.

Most of the Sun�s energy does not reach Earth�s surface. It is scattered and absorbed by the atmosphere, especially by clouds. That�s why you usually find solar-heated houses in areas that get lots of sunlight. Even in sunny places, it takes a lot of collecting plates to heat a house. Sometimes, not enough solar energy can be stored for use at night or on cloudy days. So the house needs an ordinary water heater and furnace, too.

There are different kinds of solar collectors. Concentrating collectors are much more powerful than flat-plate collectors. Concentrating collectors use curved mirrors to focus the Sun�s energy. They follow the Sun as it moves through the sky. They can produce temperatures high enough to boil water. They can be used to produce electricity.

We use small amounts of electricity from solar energy today. A photovoltaic cell is a kind of battery. It produces an electric current from solar energy. Tiny photovoltaic cells power watches and calculators. They provide electricity to satellites in space. Many photovoltaic cells linked together can produce enough electricity for an entire house.

It will become cheaper to produce electricity from solar energy as technology advances. Fossil fuels will become more expensive as they begin to run out. Solar-energy plants could become more common, once they can produce energy more cheaply than other types of power plants.

Photovoltaic cells can be used to power cars. Scientists have proposed building solar-energy stations in space. These stations would collect energy from sunlight almost 24 hours a day. Then the energy could be beamed to Earth for use.