Back cover (back panel) The back cover is also called the solar battery backplane.
The solar backsheet products are shown in Figure. The solar back sheet is composed of a solar battery back sheet film, a photovoltaic back sheet, and a photovoltaic back sheet film. The solar back sheet is located on the back of the solar panel and generally has a three-layer structure: the outer protective layer is PVDF, which has good resistance to environmental erosion; the middle layer is PET polyester film, which has good insulation properties; the inner layer is PVDF or EVA has good bonding properties.
The battery back plate is located on the back of the module (the outermost layer), which protects the solar cell module from water vapor in the outdoor environment, blocks oxygen, prevents oxidation, and has high and low temperature resistance, good insulation, aging resistance, and corrosion resistance. , Can reflect sunlight, improve the conversion efficiency of the module, and at the same time have a higher infrared emissivity, can reduce the temperature of the module.
There are two types of backplane films: one is a glue-coated composite backplane film, which is compounded with fluorine film or EVA film on both sides of the PET polyester film. The common three-layer structure is TPT, TPE, KPK, etc.; the other is Coating the backplane film, coating fluorine resin on both sides of the PET polyester film, drying and curing to form a film. The solar battery backplane is directly made of high-quality F4F3 fluororesin at high temperature through the crosslinking agent to form a film of fluororesin on the surface of the base film, which can ensure the normal operation of the module under bad weather.
Solar battery backplane materials include PET, EVA, TPT and TPE composite films.
PET is the abbreviation for polyethylene terephthalate. It has excellent physical and mechanical properties, long-term use temperature can reach 120 ℃, short-term use can withstand high temperature of 150 ℃, can withstand a low temperature of 70 ℃. High and low temperature have little effect on its mechanical properties. Excellent electrical insulation, even at high temperature and high frequency, its electrical properties are still good, creep resistance, fatigue resistance, friction resistance, and dimensional stability are all good. The gas and water vapor permeability is low, and it has excellent gas and water barrier properties. The backsheet generally uses PET film as a support. Backplanes made of multiple layers of PET also have certain market applications.
EVA is also known as fluororesin. The backplane must rely on EVA film to interact with solar energy.
The cells are glued together. In the backplane, the unmodified fluororesin and PET have poor bonding fastness to EVA. Therefore, the contact surface of the backplane and the battery sheet needs to have an adhesive layer material, which can meet the requirements of the bonding strength with EVA. The EVA adhesive layer in the backsheet usually uses polyolefin materials.
③ TPT, TPE composite membrane
TPT and TPE composite film is the most ideal protective structural material used to encapsulate solar cell modules. At present, solar cell manufacturers at home and abroad basically use TPT and TPE composite films as substrate materials for solar cells. This is because TPT and TPE composite membranes combine the “Plastic King” fluoroplastics with high-quality aging resistance, corrosion resistance, solvent resistance, pollution resistance and other properties, and polyester excellent mechanical properties, barrier properties and low water absorption, which effectively prevent Some media, especially water, oxygen, corrosive gas and liquid (such as acid rain), etc., will corrode EVA and affect solar cells. The combination of the elasticity of EVA and the toughness of TPT and TPE gives the battery a strong shock resistance.
However, if the backplane material breaks, although the battery part has not been damaged, it seems that there is no problem in the short term. However, if the backplane breaks, it will begin to be corroded by water, oxygen, acid rain and other media, and the EVA will age, crack or detach. Then it corrodes the battery part, which eventually leads to short-circuit failure of the component.
Structure of tempered glass laminated battery module.You can learn more.