PV welding tape is an important part of every mainstream solar panel, which is used to interconnect solar cells and provide connection with junction boxes. PV welding strip is tinned copper strip, with width of 1-6mm, thickness of 0.08-0.5mm and 10-30 μ M thick flux coating.
There are two types of PV strips used on PV modules: interconnection strips or bus bars and PV bus bars. Both are needed in typical silicon solar cells. The interconnection tape is directly welded on the silicon crystal to connect the solar cells in the solar panel with each other. The interconnection belt carries the current generated by the solar cell to the PV bus bar. PV bus bar is a hot-dip tinned copper conductor installed around the periphery of the solar panel. PV bus bar connects the interconnection strip to the junction box. Thin film solar panels generally only need bus bars.
PV welding strip is a key component of solar panel, which is an important factor to improve the efficiency and durability of solar panel. The high efficiency and durability of the solar panel can only be achieved by using high-quality PV welding strips properly installed in the solar panel. High quality PV welding strip can also improve the production efficiency of solar panels and reduce the scrap rate. The quality of PV welding strip and its welding to solar cells are important factors to ensure the efficiency and durability of solar panels.
1. At present, the welding strips in the market are mainly divided into silver containing and silver free welding strips. In addition to the high price, silver containing welding strips have their own advantages:
1) Increase the metallurgical bonding degree of soldering tin and the metal to be welded. The mechanical strength and conductivity will be better after welding.
2) After adding silver, the melting point of ternary alloy is lower than that of binary alloy, and its weldability and fluidity are improved
3) The resistivity will be reduced and the high temperature resistance will be improved.
2. The resistance of the strip is mainly determined by the size of the strip itself and the material of the copper substrate. The composition of the tin coating on the surface will not significantly affect the resistance of the strip. Increasing the width or thickness of the weld strip can reduce the resistance of the weld strip. This improvement can play the same role whether it is for the traditional welding method or the new type of conductive silver glue or conductive tape connection and other low-temperature connection methods. However, the strip wider than the width of the front electrode will block the incident light and cause current loss. We recommend using thicker weld strips without affecting the fragmentation rate.
3. The part of the solar cell covered by the welding strip cannot absorb sunlight. Some welding strip companies have introduced reflective welding strips. The front of the welding strip is silver plated and rolled into a longitudinal groove structure. This structure can reflect the light incident on the welding strip to the inner surface of the glass layer of the module at a certain angle, and then project it back to the battery surface after full reflection on the glass air interface. The captured light can make the module generate additional power, which can theoretically improve the module efficiency by about 2%.
4. Key quality parameters of PV welding strip
The performance index of PV weld strip is important in itself. The type and purity of copper determine the conductivity of the material and the maximum softness of the strip. The composition of flux, the thickness of its covering layer and the covering composition affect the quality of solder joints, thus affecting the durability of solar panels.
The high extensibility of the PV strip is very important to prevent solder joint failure between the bus bar and the interconnection strip. This failure may occur due to the extension/tension caused by the temperature oscillation during the operation of the solar panel. During the service life of the solar panel, the continuous, sometimes particularly intense temperature oscillation makes the solder joints undergo tests during the service life of the solar panel (25 years on average).
Two parameters that are critical to most PV strip manufacturers are bending and yield strength. Many PV strip manufacturers find it difficult to obtain a high level of strip flexibility while ensuring its straightness. Getting enough flexibility and low bending may mean the difference between winning and losing the supply contract. Therefore, manufacturers must strive to improve their rolling, annealing, tin plating and material treatment technologies to meet the increasing requirements of product performance indicators.
Therefore, the influence of the welding strip on the power generation of the module is not only the design material of the welding strip itself, but also the selection of the welding strip, the laminating process, and the quality control of the welding strip production. It is necessary to understand the welding strip from all aspects, although the industry may pay more attention to packaging materials and battery chips.