There are three common technologies used in solar panels, all of which are based on the common element silicon, which makes up a large proportion of the earth.
Monocrystalline cells are made from a thin slice or wafer cut from a single large crystal of silicon. The cells are then doped and the fine current collecting wires printed on or in the surface of the cell.
Generally monocrystalline cells have the highest efficiency, but this comes at a price. This type of cell takes more energy to make than any other, and so has a greater energy payback period, though this is usually still within five years. A number of manufacturers make monocrystalline panels, including BP Solar and Sharp Solar.
Polycrystalline cells are made from thin wafers of silicon cut from a large cast billet. The billet is not a large single crystal, but many crystals clumped together, hence the name.
Polycrystalline cells are usually slightly less efficient than moncrystalline cells, but because they are square, can be fitted into the rectangular frame of a solar panel with high space efficiency, although polycrystalline panels are still slightly larger than monocrystalline panels of the same rating. Polycrystalline cells must also have current collecting grids printed onto them. Kyocera panels use this cell technology, as do many other panels.
Amorphous/thin film panels involve deposition of very thin films of silicon or other materials directly onto a substrate such as glass or stainless steel. This technique produces a cell with a lower efficiency than the cut wafer varieties, but has the advantage of eliminating the need for inter-cell connections.
Uni-Solar makes triple junction, nine-layer thin-film amorphous panels with a much higher efficiency than the older types. The layers of silicon are deposited directly onto a stainless steel substrate and are then coated in a flexible plastic protective layer. There are now a number of manufacturers of thin-film panels, including Uni- Solar, Kaneka and Schott Solar.
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