1. The impact of photovoltaic ribbon on modules
PV ribbon is an important part of every mainstream solar panel, used to interconnect solar cells and provide connection with junction boxes. PV soldering tape is tinned copper tape, width 1-6mm, thickness 0.08-0.5mm, with 10-30μm thick flux coating.
There are two forms of PV ribbons applied to photovoltaic modules: interconnection ribbons or bus bars and PV bus bars. Both are required in a typical silicon solar cell. The interconnection tape is directly welded to the silicon crystal to connect the solar cells in the solar panel to each other. The interconnection strip brings the current generated by the solar cell to the PV busbar. The PV bus is a hot-dip tinned copper conductor installed around the periphery of the solar panel. The PV bus bar connects the interconnection tape to the junction box. Thin-film solar panels generally only need bus bars.
The PV ribbon in the solar panel is a key component and an important factor to improve the efficiency and durability of the solar panel. The high efficiency and durability of solar panels can only be achieved with high-quality PV ribbons properly installed in the solar panels. High-quality PV ribbons can also improve the production efficiency of solar panels and reduce the scrap rate. The quality of PV ribbon and its welding to solar cells are important factors to ensure the efficiency and durability of solar panels.
1. The solder ribbons currently on the market are mainly divided into silver-containing and silver-free solder ribbons. Among them, the silver ribbon has its own advantages besides the high price:
1) Increase the degree of metallurgical bonding between the solder and the welded metal. The mechanical strength and conductivity will be better after welding.
2) After adding silver, the melting point of the ternary alloy is lower than that of the binary alloy, and its solderability and fluidity are improved
3) The resistivity will be reduced and the high temperature resistance will be improved.
2. The resistance of the soldering strip is mainly determined by the size of the soldering strip and the material of the copper base material. The composition of the tin-coated layer on the surface will not significantly affect the resistance of the soldering strip. Increasing the width or thickness of the ribbon can reduce the resistance of the ribbon. This improvement can have the same effect whether it is for traditional soldering methods, or for low-temperature connection methods such as new conductive silver glue or conductive tape connection. However, a solder ribbon wider than the width of the front electrode will block the incident light and cause current loss. We recommend using thicker ribbons without affecting the fragmentation rate.
3. The part of the solar cell covered by the welding tape cannot absorb sunlight. Some welding tape companies have introduced reflective welding tape. The front side of the welding tape is silver-plated and rolled into a longitudinal groove-like structure, which can be incident on the welding tape. The light reflected at a certain angle to the inner surface of the glass layer of the module, is totally reflected at the glass-air interface and then projected back to the battery surface. The captured light allows the module to generate additional power, which can theoretically increase the efficiency of the module by about 2%.
4. The key quality parameters of PV ribbon
The performance indexes of PV ribbon are important in themselves. The type of copper and its purity determine the conductivity of the material and the maximum softness that the ribbon can achieve. The composition of the flux, the thickness of the covering layer and the covering composition affect the quality of the solder joints and thus the durability of the solar panel.
The high extensibility of the PV ribbon is very important to prevent the solder joint failure between the bus bar and the interconnect ribbon. This failure may occur due to the extension/tension caused by the temperature oscillation changes during the operation of the solar panel. The continuous and sometimes extremely intense temperature oscillations during the service life of solar panels make the solder joints withstand the test during the service life of the solar panels (25 years on average).
Two parameters that are critical to most PV ribbon manufacturers are camber and yield strength. Many PV ribbon manufacturers find it difficult to obtain a high level of ribbon flexibility while ensuring its straightness. Obtaining sufficient softness and low camber may mean the difference between winning and losing supply contracts. Manufacturers must therefore strive to improve their rolling, annealing, tinning, and material processing technologies to meet the ever-increasing product performance requirements.
Therefore, the influence of the welding ribbon on the power generation of the components is not only the design material of the welding ribbon itself, but also the selection of the welding ribbon, the lamination process, and the quality control of the welding ribbon production. We need to understand the solder ribbon from all aspects, although the industry may focus more on packaging materials and solar cells.
2. Common welding ribbon specifications
Automatic spool mounted tin-coated copper tape
◆Copper base: imported refined ductile oxygen-free copper/T2 copper, copper content ≥99.99%, conductivity ≥98%
◆Cu base resistivity: oxygen-free copper≤0.0165Ωmm2/mT2 copper≤0.0172Ωmm2/m
◆Coating composition: 62%Sn36%Pb2%Ag (optional)
◆Coating thickness: 0.01～0.05mm single-sided coating, uniform coating, bright and smooth surface.
◆Coating melting point: 179℃
◆Tensile strength: soft state≥25kgf/m㎡ semi-soft state≥30kgf/m㎡
◆Welding ribbon elongation: soft state≥35%3/4 soft state≥25%1/2 soft state≥15%
◆Width error: ±0.1mm
◆Thickness tolerance: Interconnect belt ±0.01mm, busbar ±0.015mm
Lead and silver tin coated copper strip
◆Coating composition: 63%Sn36%P2%Ag (optional)
Lead-containing tin coated copper strip
◆Coating composition: 63%Sn37%Pb, 603%Sn40%Pb (optional)
◆Coating thickness: 0.01～0.05mm single-sided coating, uniform coating, bright and smooth surface.
◆Coating melting point: 183℃, 190℃
Lead-free environmentally friendly tin-coated copper strip
◆Coating composition: 96.5%Sn3.0Ag0.5%Cu, 96.5%Sn3.5Ag (optional)
◆Coating thickness: 0.01～0.05mm single-sided coating, uniform coating, bright and smooth surface.
◆Coating melting point: 217℃, 221℃
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