Photovoltaic cells produce direct-current (DC) electricity. About 40 cells are joined together in enclosed, protective casings called modules. About ten of these modules are mounted in one PV panel. These flat-plate PV panels can be mounted facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. About ten to 20 PV panels can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single, large PV system.
Two primary types of PV technologies available commercially are crystalline silicon and thin film. In crystalline-silicon technologies, individual PV cells are cut from ingots of crystalline silicon. In thin-film PV technologies, the PV material is deposited on glass or thin metal that mechanically supports the module. Thin-film-based modules are produced in sheets that are sized for specified electrical outputs.
Several companies have started integrating PV products into building materials. For example, PV shingles look like traditional asphalt shingles and can be installed by roofers. Other similar technologies are standing-seam metal roofs incorporating PV and modules that look like slate roofing materials. Soon to be widely available is glass for windows and skylights that generates electricity. The benefit of these technologies is that they replace building materials that you would buy anyway.
The cost over 20 years will amount to between 20 and 40 cents per kilowatt-hour. However, costs will vary quite a bit depending on your location, solar resources, and available subsidies.
In addition to PV modules, the components needed to complete a PV system may include a battery charge controller, batteries, an inverter or power control unit (for alternating-current loads), safety disconnects and fuses, a grounding circuit, and wiring.
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