Panels on a rooftop collect energy from sunlight and convert it directly into electricity. The solar panels contain semiconducting materials. When light strikes the material, electrons move from one layer of the material to another, forming an electric current.
Solar Energy
Solar Energy,radiationproducedby nuclear fusion reactions deep in the Sun's core. The Sun provides almost all the heat and light Earth receives and therefore sustains every living being.
Solarenergytravelsto 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 total radiation power (1.4 kilowatts per square meter, called the solar constant) varies only slightly, about 0.2 percent every 30 years. Any substantial change would alter or end life on Earth.
Solar Energy Storage Devices
Becauseoftheintermittent nature of solar radiation as an energy source, excess solar energy produced during sunny periods must be stored. Insulated tanks commonly store this energy in hot water. Batteries often store excess electric energy produced from wind or photovoltaic devices. One possibility for the future is the use of excess solar-generated electric energy as a supplemental source for existing power networks. Uncertain economics and reliability, however, make this plan difficult to implement.
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