Kids Research Express

. For applications such as air conditioning, central power generation, and many industrial heat requirements, flat plate collectors cannot provide carrier fluids at high enough temperatures to be effective. They may be used as first-stage heat input devices; the temperature of the carrier fluid is then boosted by other conventional heating means. Alternatively, more complex and expensive concentrating collectors can be used. These devices reflect the Sun’s rays from a large area and focus it onto a small, blackened receiving area. The light intensity is concentrated to produce temperatures of several hundred or even several thousand degrees Celsius. The concentrators move to track the Sun using devices called heliostats. Concentrators use curved mirrors with aluminum or silver reflecting surfaces that coat the front or back surfaces of glass or plastic. Researchers are developing cheap polymer films to replace the more expensive glass. One new technique uses a pliable membrane stretche...

. People have devised two main types of artificial collectors to directly capture and utilize solar energy: flat plate collectors and concentrating collectors . Both require large surface areas exposed to the Sun since so little of the Sun’s energy reaches Earth’s surface. Even in areas of the United States that receive a lot of sunshine, a collector surface as big as a two-car garage floor is needed to gather the energy that one person typically uses during a single day. A. Flat Plate Collectors Flat plate collectors are typically flat, thin boxes with a transparent cover that are mounted on rooftops facing the Sun. The Sun heats a blackened metal plate inside the box, called an absorber plate, that in turn heats fluid (air or water) running through tubes within the collector. The energy transferred to the carrier fluid, divided by the total solar energy that falls on the collector, is called the collector efficiency. Flat plate collectors are typically capable of heating carrier flu...

. People can make indirect use of solar energy that has been naturally collected. Earth's atmosphere, oceans, and plant life, for example, collect solar energy that people later extract to power technology. The Sun's energy, acting on the oceans and atmosphere, produces winds that for centuries have turned windmills and driven sailing ships (see Wind Energy ). Modern windmills are strong, light, weather-resistant, aerodynamically designed machines that produce electricity when attached to generators. Approximately 30 percent of the solar power reaching Earth is consumed by the continuous circulation of water, a system called the water cycle or hydrologic cycle. The Sun’s heat evaporates water from the oceans. Winds transport some of the water vapor from the oceans over the land where it falls as rain. Rainwater seeps into the ground or collects into streams or lakes and eventually returns to the ocean. Thus, radiant energy from the Sun is transformed to potential energy of wa...

Solar Energy, radiation produced by nuclear fusion reactions deep in the Sun’s core (see Nuclear Energy ). The Sun provides almost all the heat and light Earth receives and therefore sustains every living being. Solar energy travels to Earth through space in discrete packets of energy called photons (see Electromagnetic Radiation ). On the side of Earth facing the Sun, a square kilometer at the outer edge of our atmosphere receives 1,400 megawatts of solar power every minute, which is about the capacity of the largest electric-generating plant in Nevada. Only half of that amount, however, reaches Earth’s surface. The atmosphere and clouds absorb or scatter the other half of the incoming sunlight. The amount of light that reaches any particular point on the ground depends on the time of day, the day of the year, the amount of cloud cover, and the latitude at that point. The solar intensity varies with the time of day, peaking at solar noon and declining to a minimum at sunset. The t...