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Characteristics of Several Major Encapsulation Materials for Solar Panels First, tempered glass

Source:Bluesolaria    Time:2019-08-12
1. Processing principle   
Tempered glass is a secondary processing product of flat glass. The processing of tempered glass can be divided into physical tempering method and chemical tempering method. The solar photovoltaic module has a high transmittance for tempered glass, which is greater than 91.6%, and has a higher reflectance for infrared light greater than 1200 nm. The thickness is 3.2mm.
1) Physical tempered glass is also called quenched tempered glass (heating the metal workpiece to a suitable temperature for a period of time, then immersing it in a quenching medium for rapid cooling). This kind of glass is under internal tension and externally stressed. Once local damage occurs, stress is released and the glass is broken into numerous small pieces. These small pieces have no sharp edges and are not easy to injure people.
2) Chemically tempered glass increases the strength of the glass by changing the chemical composition of the surface of the glass, and is generally tempered by ion exchange. The effect is similar to physical tempered glass
2. The main advantages of tempered glass:
The first is that the strength is several times higher than that of ordinary glass, the bending strength is 3 to 5 times that of ordinary glass, and the impact strength is 5 to 10 times that of ordinary glass, which improves the strength and improves the safety.
The second is safe use, and its load-bearing capacity is improved to improve the fragile nature. Even if the tempered glass breaks down, it will show small fragments without sharp angles, and the damage to the human body is greatly reduced. The tempered glass has better resistance to quenching and rapid heat than ordinary glass. It has a 2~3 times improvement and can generally withstand temperature changes above 150LC, which has obvious effects on preventing thermal cracking. Tempered glass has good thermal stability and can withstand a temperature difference of three times that of ordinary glass, and can withstand a temperature difference of 200 °C.
3. Disadvantages of tempered glass:
First, the tempered glass can no longer be cut and processed, and the glass can only be processed to the required shape before tempering, and then tempered.
Second, although the strength of tempered glass is stronger than that of ordinary glass, tempered glass has the possibility of self-explosion (self-rupture) when the temperature difference changes greatly, and ordinary glass does not have the possibility of self-explosion. The automatic explosion of tempered glass under the action of no direct mechanical external force is called self-explosion of tempered glass.
4. The role of tempered glass
Enhance the impact resistance of the solar panel, good light transmission can improve the efficiency of the solar panel and seal the solar panel.
5. Storage conditions of tempered glass
The glass should be protected from light and moisture, and stacked flat. Cover the glass with a dust cloth.
The best storage conditions for glass: in a constant temperature, dry warehouse, the temperature is 25 ° C, the relative humidity is less than 45%, the glass should be clean and free of steam, and must not touch the glass and EVA contact surface with bare hands.
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Second, EVA
1. The principle of EVA
1) The performance of EVA depends mainly on the molecular weight (expressed by the melt index MI) and the content of vinyl acetate (expressed as VA). When MI is constant, the elasticity, flexibility, cohesiveness, compatibility and transparency of VA are improved, and the content of VA is lowered, which is close to the performance of polyethylene. When the VA content is constant, the MI decreases, the softening point decreases, and the workability and surface gloss are improved, but the strength is lowered, the molecular weight is increased, and the impact resistance and stress cracking resistance are improved.
2) Different temperatures have a greater impact on the degree of cross-linking of EVA. The degree of cross-linking of EVA directly affects the performance and service life of the solar panels. In the molten state, EVA is bonded to the crystalline silicon solar cell sheet, glass, and TPT, and there are both physical and chemical bonding in the process. The unmodified EVA is transparent, soft, has hot melt adhesion, has a low melting temperature, and has good melt flowability. However, its heat resistance is poor, easy to extend and low in elasticity, low in cohesive strength and poor in creep resistance, and it is easy to cause thermal expansion and contraction, which causes chip fragmentation and delamination of the bond. EVA cross-linking is generally between 70% and 85%, with glass peel strength of 35N, and TPT20N.
3) Modifying EVA by chemical cross-linking by adding an organic peroxide cross-linking agent to EVA. When EVA is heated to a certain temperature, the cross-linking agent decomposes to generate free radicals, which triggers EVA molecules. The combination of the three-dimensional network structure results in the cross-linking and solidification of the EVA adhesive layer. When the degree of crosslinking reaches 60% or more, it can withstand the change of the atmosphere, and no thermal expansion and contraction occurs.
2. The role of EVA
1) Encapsulate the solar cell to prevent the external environment from affecting the electrical performance of the solar cell.
2) Enhance the light transmission of the solar panel.
3) Bond the solar cell piece, tempered glass and TPT together to have a certain bonding strength.
Note: Although EVA can function as encapsulating solar panel, EVA has water absorption.
3. EVA storage environment
EVA film should be protected from light, heat, and moisture, and stacked. The best storage conditions for EVA film: placed in a constant temperature, constant humidity warehouse, the temperature is between 0-30 ° C, the relative humidity is less than 60%. Avoid direct sunlight and should not be near places with heating equipment or dust, and should pay attention to fire prevention. The warranty period is half a year.
Third, TPT (backsheet)
TPT is used on the back side of the solar panel assembly and is one of the main encapsulation materials.
1. Structure of TPT (backsheet)
The backing film consisting of PVF (polyvinyl fluoride film)-PET (polyester film)-PVF three-layer film, referred to as TPT for short; TPT has three-layer structure: outer protective layer PVF, with good resistance to environmental erosion, the middle layer is the polyester film (PET) which has good insulation properties, and the inner layer PVF has good adhesion to the surface treatment and EVA. The TPT must be kept clean and free of dirt or moisture, especially if the inner layer is not in direct contact with your fingers to avoid affecting the bonding strength with EVA.
2. Characteristics of TPT (backsheet)
It has good weather resistance, excellent mechanical properties, ductility, aging resistance, corrosion resistance, air resistance, and resistance to many chemicals, solvents and colorants. Excellent anti-aging properties and maintains toughness and flexibility over a wide temperature range.
3. The role of TPT (backsheet)
The white TPT reflects the sunlight and increases the energy absorption rate of the solar panel. Therefore, the efficiency of the solar panel is slightly improved, and because of its high infrared emissivity, the operating temperature of the solar panel can also be lowered, and the efficiency of the solar panel is also improved.
Enhances the water resistance of the solar panels.
Provides a good seal protection for the back of the solar panel assembly, extending the life of the assembly
Improve the insulation properties of the solar panels.
4.TPT (backsheet) storage environment
The backing film should be protected from light, heat, and moisture, and stacked. The best storage conditions for the backing film: in a constant temperature, constant humidity warehouse, the temperature is between 0-40 ° C, the relative humidity is less than

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