ELECTRICITY FROM THE SUN
Almost like magic, solar cells convert sunlight directly into electricityour most versatile form of energy. Today solar-generated electricity serves people living in the most isolated spots on earth and in the center of our biggest cities. First used in the space program, PV systems are now generating electricity to pump water, light up the night, activate switches, charge batteries, supply the electric utility grid, and more. Whether you are a homeowner, planner, architect, or just someone who pays electric utility bills, photo- voltaics may already touch your life in some way.
A High-Tech Industry
Solar electric systems are simple to operate and have no moving parts; however, PV cells employ sophisticated semiconductor devices, many of which are similar to those developed in the integrated circuit industry over the last 35 years. PV cells operate on the physical principle that electric current will flow between two semiconductors with different electrical properties when they are put in contact with each other and exposed to light. A collection of these PV cells constitutes a PV panel, or module.
PV modules, because of their electrical properties, produce direct rather than alternating current (ac). Direct current (dc) is electric current that flows in a single direction. Many simple devices, such as those that run on batteries, use direct current. Alternating current, in contrast, is electric current that reverses its direction at regular intervals. This is the type of electricity provided by utilities and required to run most modern appliances and electronic devices.
In the simplest systems, dc current produced by PV modules is used directly. In applications where ac current is necessary, an inverter can be added to the system to convert the dc current to ac current.
PV research and development, supported by the U.S. Department of Energy (DOE), private industry, and universities, has improved the performance and substantially reduced the cost of PV. Researchers continue to experiment with various combinations of materials to increase the amount of electricity generated and reduce the cost of manufacturing.
The U.S. industrial partners in this PV research and development have built a domestic energy industry with sales totaling about $135 million in 1992. (U.S. companies account for about 37% of the worldwide market for PV.) About two-thirds of this production is exported. Both domestic and international market analysts, meanwhile, predict substantial growth for U.S.-manufactured PV products in the future.
PV Has Advantages
PV offers advantages over diesel generators, primary (one-time use) batteries, and conventional utility power.
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Written by: National Renewable Energy Laboratory
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