An immense amount of energy from the sun strikes the surface of the earth every day. This energy may be captured and used in the form of heat in "solar thermal" applications, or it may be converted directly into electricity to power electrical devices using photovoltaic cells
Photovoltaic (PV) cells convert sunlight into electricity. New technologies are improving the energy conversion efficiency of PV cells and decreasing the manufacturing cost. PVs are used in many applications now and the market is expanding quickly.
A conventional solar cell consists of a wafer of silicon that is about 1/50th of an inch thick. Typical cells that are four inches in diameter produce about one watt of power, and are grouped into modules of dozens of cells. Modules are further grouped into panels and then arrays, which may produce several kilowatts of power.
Homes can use photovoltaic systems to replace or supplement electric power from the utility. A stand-alone residential system consists of solar panels (A), a battery to store power for use at night (B), and a device called an "inverter" to allow conventional appliances to be powered by solar electricity (C). Some systems use appliances specially designed to be powered by solar electricity and do not require an inverter.
B.
C.
This is actually the first step of a plan involving one million houses in during the next couple of years. In utility-connected systems, the electric company acts as a back-up power source. If the home needs power in excess of that produced by the solar panels, it uses utility power. If the solar panels produce power in excess of the energy requirements of the home, it is sold to the utility. In the United States, a 1978 law called the Public Utility Regulatory Power Act (PURPA) requires that utilities buy privately produced power.
For additional information see the Photovoltaic Theory page.
