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Solar modules generally need to be placed in the natural environment, weathered various environments.  The backplane, as the "harem" guard of the component, must be somewhat defensible against various environments. 

 

Ⅰ. Foreword

At present, there are many kinds of backplanes in the market, but the premise must have reliable insulation, water resistance and aging resistance.  Different manufacturers and different structures have different naming methods, such as TPT, TPE, KPK, KPE, AAA, PET, PET-PET, PPPE.FPF, FPE and so on. 

Among them:  

T: DuPont's polyvinyl fluoride (PVF) film, marketed as Tedlar.  

K: refers to the PVDF patent trademark K (Kynar) produced by Arkema Company.  

P: Refers to PET film -- polyethylene terephthalate film (skeleton of backplane).  

E: EVA(low VA content), or polyolefin PO.  

A: Modified polyamide (PA,Nylon for short) Isovolta developed with AAA structure back.  

F: refers to fluorocarbon coating: PTFE(polytetrafluoroethylene) coating;  PVDF(polyvinylidene fluoride) coating;  Copolymer of FEVE fluoroethylene and vinyl ether.  Of course, many coating backplane manufacturers in order to emphasize the quality of their products, but also called F "T". 

Ⅱ. Common problems of backplanes

1、Yellow stain

In the process of solar photovoltaic module lamination, two layers of adhesive film are used to bond the solar cell, so that the solar cell is integrated with the glass and the backplane.  

Two layers of adhesive film will generally have a layer of shortwave uv cutoff.  The backplane itself has a certain resistance to UV intensity of 300nm-380nm, but part of the backplane still yellows under uv light, resulting in the destruction of the molecular components of the backplane, the overall performance of the backplane decreases, and the reflectivity of the backplane decreases, affecting the overall output of the component.  

Fluorine - containing materials have the ability to withstand ultraviolet light without other treatment.  If both layers fail to cut off the UVB rays, the uVB rays will directly cause the underlying backplane to turn yellow.  

Impact: First of all, the appearance of the component is not beautiful. In addition, the backplane after yellowing will reduce the reflection of sunlight, which will affect the solar cell's absorption effect of sunlight, and ultimately reduce the power output of the component. 

2、The back bulge

The position where the battery has hot spots and the position of invisible tape are prone to backplane bulge, especially when the two positions overlap, which is mainly caused by material gasification due to high temperature.  

In the application process of the component, part of the sunlight absorbed by the battery itself will be converted into heat energy, causing the internal temperature of the component to rise. The ULTRAVIOLET absorbent in EVA will convert the absorbed ultraviolet light into part of heat energy and send it out into the component.  

Generally speaking, the normal working temperature of the component is between 70℃ and 80℃. According to the test data, the temperature rise will affect the power output of the component. Every temperature rise of the component itself is 1℃, the output power of the component will be reduced by about 1W.  

The heat conduction coefficient is related to the substrate and composition of the backplane itself, and the heat is mainly conducted by the medium. 

 

Take measures: in the battery input, ensure that the input battery is qualified, in the standard battery, to avoid welding, virtual welding and other situations in the welding process, in accordance with the drawings to paste invisible tape. 

3、Bubbles under the backplane
Cause: The backplane strip causes a large gradient between the bus belt, and the laying staff does not put the EVA strip in place, resulting in the EVA is not well filled. 

Impact: In the later use of the component, the bubble will gradually expand and the material around the bubble will be oxidized and deteriorated, which will greatly affect the service life of the component. 

4、The back scratch

Cause: The raw material itself has its own problems, not found in the raw material inspection process, directly into the production workshop;  When the laminate after laying is transported on the transmission line, sharp objects on the transmission line cause a notch on the backplane;  Damage to the backplane caused by trimming personnel during trimming. 

Impact: The backplane provides the following functions for components: prevent moisture, dust, and insulation.  The moisture resistance of a component scratched on the backplane is greatly reduced, which accelerates the oxidation of the component and reduces the safety performance of the component.  Increasing the water permeability of the backplane will lead to more water vapor inside the component, which will directly lead to corrosion of the internal circuit. If used for a long time, the component will lose its power generation performance, and the internal circuit will also be damaged due to serious oxidation, thus ending the life of the component.

Preventive measures: strengthen inspection, timely find the raw material itself with backplane scratches and backplane defects;  Before the normal operation of each shift, check whether there are sharp objects on the transmission line;  Do not knock against the backplane when the component laminate is transported on the transmission line. 

5、Defect of bonding layer with EVA
Impact: The peel strength is not enough with EVA, and the adhesive force measured by universal tension machine is less than 40N/cm.  

Preventive measures: The backplane is treated with corona before use to increase adhesion delamination and reduce dust deposition on the backplane surface. 

 

Ⅲ、Evaluation index and inspection method of backplane

Ⅳ、Epilogue

The material and quality of the backplane determine the service life of components, and people begin to pay more and more attention to the service life of components.  How to ensure the quality of the backplane becomes more important.