A solar cell (also called a photovoltaic cell) is an electrical device that converts theenergy of light directly into electricity by the photovoltaic effect. It is a formof photoelectric cell (in that its electrical characteristics—e.g. current, voltage, orresistance—vary when light is incident upon it) which, when exposed to light, cangenerate and support an electric current without being attached to any external voltagesource.The term "photovoltaic" comes from the Greek φ ς (ῶ phōs) meaning "light", and from"Volt", the unit of electro-motive force, the volt, which in turn comes from the last nameof the Italian physicist Alessandro Volta, inventor of the battery (electrochemical cell).The term "photo-voltaic" has been in use in English since 1849.Photovoltaics is the field of technology and research related to the practical applicationof photovoltaic cells in producing electricity from light, though it is often usedspecifically to refer to the generation of electricity from sunlight. Cells can be describedas photovoltaic even when the light source is not necessarily sunlight (lamplight, artificiallight, etc.). In such cases the cell is sometimes used as a photodetector (forexample infrared detectors), detecting light or other electromagnetic radiation near thevisible range, or measuring light intensity.The operation of a photovoltaic (PV) cell requires 3 basic attributes:The absorption of light, generating either electron-hole pairs or excitons.The separation of charge carriers of opposite types.The separate extraction of those carriers to an external circuit.In contrast, a solar thermal collector collects heat by absorbing sunlight, for the purposeof either direct heating or indirect electrical power generation. "Photoelectrolytic cell"(photoelectrochemical cell), on the other hand, refers either a type of photovoltaic cell(like that developed by A.E. Becquerel and modern dye-sensitized solar cells) or a devicethat splits water directly into hydrogen and oxygen using only solar illumination.
A solar panel (also solar module, photovoltaicmodule or photovoltaic panel) is a packaged, connectedassembly of photovoltaic cells. The solar panel can beused as a component of a larger photovoltaic system togenerate and supply electricity in commercial andresidential applications. Each panel is rated by its DCoutput power under standard test conditions, andtypically ranges from 100 to 320 watts.The efficiency of a panel determines the area of a panelgiven the same rated output - an 8% efficient 230 wattpanel will have twice the area of a 16% efficient 230watt panel. Because a single solar panel can produce onlya limited amount of power, most installations containmultiple panels. A photovoltaic system typically includesan array of solar panels, an inverter, and sometimesa battery and or solar tracker and interconnection wiring.
Rigid thin-filmmodulesIn rigid thin film modules, the cell and the moduleare manufactured in the same production line.The cell is created on a glass substrateor superstrate, and the electrical connections arecreated in situ, a so-called "monolithic integration".The substrate or superstrate is laminated with anencapsulant to a front or back sheet, usually anothersheet of glass.The main cell technologies in this category are CdTe,or a-Si, or a-Si+uc-Si tandem, or CIGS (orvariant). Amorphous silicon has a sunlight conversionrate of 6-12%.
Flexible thin-filmmodulesFlexible thin film cells and modules are created on the sameproduction line by depositing the photoactive layer and othernecessary layers on a flexible substrate.If the substrate is an insulator (e.g. polyester or polyimide film)then monolithic integration can be used.If it is a conductor then another technique for electricalconnection must be used.The cells are assembled into modules by laminating them to atransparent colorless fluoropolymer on the front side(typically ETFE or FEP) and a polymer suitable for bonding to thefinal substrate on the other side. The only commercially available(in MW quantities) flexible module uses amorphous silicon triplejunction (from Unisolar).
Solar micro-inverterSeveral companies have begun embedding electronicsinto PV modules. This enables performing maximumpower point tracking (MPPT) for each moduleindividually, and the measurement of performance datafor monitoring and fault detection at module level. Someof these solutions make use of power optimizers, a DC-to-DC converter technology developed to maximize thepower harvest from solar photovoltaic systems. As ofabout 2010, such electronics can also compensate forshading effects, wherein a shadow falling across asection of a panel causes the electrical output of one ormore strings of cells in the panel to fall to zero, but nothaving the output of the entire panel fall to zero.