Flat-Plate Photovoltaic Modules
Flat-plate photovoltaic (PV) modules are made of several components, including the front surface materials, encapsulant, rear surface, and frame.
Front Surface Materials
The front surface of a flat-plate PV module must have a high transmission in the wavelengths that can be used by the solar cells in the module. For example, for silicon solar cells, the top surface must have high transmission of light with wavelengths from 350 to 1200 nm.
Also, reflection from the front surface should be minimal. An antireflection coating added to the top surface can greatly reduce the reflection of sunlight, and texturing of the surface can cause light that strikes the surface to stay within the cells. Unfortunately, these textured modules are not "self-cleaning," and the advantage of reduced reflection is usually outweighed by losses because of dust sticking to the surface.
The top surface should also be impervious to water, be able to resist damage from hail, be stable under long-term exposure to ultraviolet radiation, and have low thermal resistivity. If water, as liquid or vapor, is able to get inside a PV module, it corrode the metal contacts and interconnects, which will greatly shorten the life span of the module.
A common front surface material is tempered, low-iron glass, which is low-cost, strong, stable, highly transparent, and impervious to water and gases. It also has self-cleaning properties.
An encapsulant helps hold together the top surface, PV cells, and rear surface of the PV module. The encapsulant must be stable at high temperatures and high levels of ultraviolet radiation. It must also be optically transparent and have a low thermal resistance. Ethyl vinyl acetate—or EVA—is the most commonly used encapsulant. Thin sheets of EVA are inserted between the solar cells and the top and rear surfaces. Heating this "sandwich" causes the EVA to polymerize, thus bonding the module into one piece.
The material used as the rear surface of the PV module must have low thermal resistance and prevent the ingress of water and gases. In many modules, the rear surface material is a thin polymer sheet, typically made of Tedlar.
The final structural component of the module is the frame, which is typically made of aluminum.
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