Learning from the word itself, the prefix “photo” means “produced by light,” and the suffix “voltaic” refers to “electricity produced by a chemical reaction.” PV technology produces electricity directly from the electrons freed by the interaction of sunlight with certain semiconductor materials, such as silicon, in the PV module. The electrons are collected to form a direct current (DC) of electricity. Photovoltaic or Solar Electric or PV System converts light (not heat) energy of the sun into electrical energy (Direct Current DC) electricity. This DC current is converted to AC current with an Inverter. The AC electricity can be used to power electric loads or deposit with utility grid to be pulled back later for consumption. The electrical energy produced by PV system can also be used for charging (storage) batteries.
These cells are made from very pure monocrystalline silicon. The silicon has a single and continuous crystal lattice structure with almost no defects or impurities. The principle advantage of monocrystalline cells are their high efficiencies, typically around 15%, although the manufacturing process required to produce monocrystalline silicon is complicated, resulting in slightly higher costs than other technologies. Monocrystalline cells loose high output efficiencies under low sunlight and high heat conditions.
Polycrystalline Silicon Cells:
Polycrystalline cells are produced using numerous grains of monocrystalline silicon. In the manufacturing process, molten polycrystalline silicon is cast into ingots; these ingots are then cut into very thin wafers and assembled into complete cells. Multicrystalline cells are cheaper to produce than monocrystalline ones, due to the simpler manufacturing process. However, they tend to be slightly less efficient but perform relatively better under high heat conditions.
Amorphous Silicon:
Amorphous silicon cells are composed of silicon atoms in a thin homogenous layer rather than a crystal structure. Amorphous silicon absorbs light more effectively than crystalline silicon, so the cells can be thinner. For this reason, amorphous silicon is also known as a "thin film" PV technology. Amorphous silicon can be deposited on a wide range of substrates, both rigid and flexible, which makes it ideal for curved surfaces and "roll-away" modules. Amorphous cells are, however, less efficient than crystalline based cells, but they perform better under low sunlight and high heat conditions.
Other Thin Films:
A number of other promising materials such as cadmium telluride (CdTe) and Copper indium gallium (di)selenide (CIGS) are now being used for PV modules. The attraction of these technologies is that they can be manufactured by relatively inexpensive industrial processes, certainly in comparison to crystalline silicon technologies, yet they typically offer higher module efficiencies than amorphous silicon but lower efficiencies than mono or poly crystalline cells.