Crystalline Photovoltaic Modules
Solar cells are rarely used individually. Because the amount of power produced by a single cell is relatively small, designers group solar cells together to form electrical modules that supply a more useful level of voltage, current and power (Figure on the left). Modules are the basic building blocks of a photovoltaic system.
Modules contain a number of PV cells connected in series or parallel to obtain desired voltage and current and are encapsulated to protect them from the environment. Solar modules are most often used in harsh and remote environments, where it is not feasible to supply power by the grid or fuel dependent systems. Hence modules must be capable of extended, maintenance free operation for 30 or more years. Encapsulation is the major contributor to solar cell life expectancy. The module must be able to withstand such environmental conditions as dust, salt, sand, wind, snow, humidity and hail, as well as maintaining performance under prolonged exposure to UV light. In a standard PV module solar cells are embedded in a laminate (usually with a heat strengthen glass front plate) on the top, a waterproof Ethylene Vinyl Acetate (EVA) encapsulant and a soft pliable polymer backing material such as Tedlar®.
Figure on the right shows the structure of a typical PV module. The top low iron cover glass must have, and maintain, high transmission in the waveband 350 to 1200 nm. An aluminium frame may be added to provide rigidity and a means for mounting the module. Positive and negative terminals are inside a junction box mounted on the back of the module.
Some specialized PV modules use glass on both the front and back of the module. Known as laminates, the photovoltaic cells are encapsulated with special multi-component PVB based resin between two pieces of special low iron tempered glass. Glass-on-glass solar modules without an aluminum frame are mostly used for custom building integrated applications, due to the fact that standard PV modules can not be utilized in building envelope applications.