Life of module is one of the important factors to measure module quality. The working life of the modules and the packaging materials
The material and packaging process have a great relationship. Packaging materials play an important role in solar cells. For example, glass, EVA, glass fiber, and TPT also have an impact on the output power of the packaged module. The materials, parts and structures used in the modules are required to be consistent with each other in terms of service life, so as to avoid failure of the entire module due to one damage.
(1) Upper cover
The upper cover plate covers the front of the solar cell module and constitutes the outermost layer of the module. It must have a high light transmittance and be strong to protect the battery for a long time. The materials for the upper cover plate are: tempered glass, polyacrylic resin, fluorinated ethylene propylene, transparent polyester, polycarbonate, etc.
The encapsulation glass used in solar cells, the current mainstream product is low-iron tempered embossed glass, which is used in solar energy
In the wavelength range of the battery’s spectral response (320~1100nm), due to its extremely low iron content (less than 0.015%), its light transmittance is extremely high (about 91% in the 400~1100nm spectral range). Seen from its edge, it is white, so it is also called white glass. It has a high reflectivity for infrared rays greater than 1200nm.
In addition, tempering the glass not only maintains a high light transmittance, but also increases the strength of the glass to 3 to 4 times that of ordinary flat glass. The glass tempering process helps to improve the ability of solar cell modules to resist hail and accidental blows, and to ensure that the entire solar cell module has sufficiently high mechanical strength. In order to reduce the reflection of light, some anti-reflective treatments can be performed on the glass surface, which can be made into “anti-reflective glass”. The main measure is to coat a thin film layer on the glass surface to reduce the reflectivity of the glass.
Resins include room temperature curing silicone rubber, fluorinated ethylene propylene, polyvinyl butyral, transparent hydrogen peroxide resin, polyvinyl acetate and the like. The general requirements are as follows: 1 has high light transmittance in the visible light range; 2 has flexibility; 3 has good electrical insulation properties; 4 can be applied to automated module packaging. Resin encapsulation is a simple form of solar cell encapsulation, which adopts simple measures to encapsulate and protect the solar cell, and the cost of materials used is relatively low. With its flexibility and low price, it is widely used in small solar products, such as: solar lawn lights, solar chargers, solar teaching appliances, solar toys, solar road signs and solar signal lights.
(3) Organic silica gel
The basic structural unit of organic silicon products is composed of silicon-oxygen chain links, and the side chains are connected to various other organic groups through silicon atoms. Silicone is not only resistant to high temperature, but also resistant to low temperature, and can be used in a wide temperature range. Whether it is chemical properties or physical and mechanical properties, the change with temperature is very small. Organic silicon products have good electrical insulation properties, and their dielectric loss, voltage resistance, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best in insulating materials. Moreover, their electrical properties are little affected by temperature and frequency, and the cured silicone is colorless and highly transparent.
(4) EVA film
EVA is also called solar cell glue film, used to bond glass and solar cell array, solar cell array and TPT film, and its light transmittance is good. Standard solar cell modules generally need to add two layers of EVA film. The EVA film acts as a bond between the battery and the glass, and between the battery and the TPT. EVA is a copolymer of ethylene and vinyl acetate. The unmodified EVA has the characteristics of transparency, softness, hot melt adhesion, low melting temperature and good melt fluidity. These characteristics meet the requirements of solar cell sealing, but its heat resistance is poor, easy to extend, low elasticity, low cohesive strength, easy to produce thermal shrinkage and cause the solar cell to break and delaminate the adhesion. In addition, as solar cell modules are used outdoors for a long time, whether the EVA film can withstand outdoor ultraviolet aging and thermal aging is also a very important issue. The EVA solar cell film made by heating and extruding with EVA as raw material, adding suitable modifiers, etc., is convenient for cutting operation at room temperature; the solar cell module is laminated and sealed according to heating and curing conditions, and a permanent adhesive seal is formed after cooling. The glass fiber layer is woven with glass fiber to remove air bubbles that may be sealed in the battery panel during lamination.
(5) Back material
Generally tempered glass, aluminum alloy, plexiglass, TPT, etc. TPT is used to prevent water vapor from entering the solar cell module and reflect sunlight. Because of its high infrared reflectivity, it can reduce the working temperature of the module and also help improve the efficiency of the module. The thickness of the TPT film is 0.12mm, and the average reflectivity is 0.648 in the 400-1100nm spectral range.
At present, TPT composite film is mostly used, which has the following requirements: ①It has good weather resistance, can withstand outdoor temperature changes, ultraviolet aging and thermal aging, etc.; ②There is no change in the lamination temperature; ③It is firmly combined with the bonding material.
Flat panel modules must have a frame to protect the modules, and the framed modules form a square matrix. The frame uses an adhesive to form a seal to the edge of the module. The main materials are stainless steel, aluminum alloy, rubber, reinforced plastics, etc.