Technical dry goods The impact of photovoltaic ribbon on modules and common specifications!

release time:

2022-08-22

PV ribbons are an essential component of every mainstream solar panel, interconnecting solar cells and providing connections to junction boxes. PV ribbons are tinned copper ribbons with a width of 1-6mm, a thickness of 0.08-0.5mm, and a flux coating of 10-30μm thick.

1. The influence of photovoltaic ribbon on modules

There are two forms of PV ribbons used in photovoltaic modules: interconnection ribbons or bus bars and PV bus bars. Both are required in a typical silicon solar cell. Interconnect ribbons are soldered directly to the silicon crystals to interconnect the solar cells in the solar panel. The interconnecting strips bring the current generated by the solar cells to the PV busbars. PV busbars are hot-dip tinned copper conductors installed around the perimeter of the solar panel. PV busbars connect the interconnect strips to the junction boxes. Thin-film solar panels generally require only bus bars.

PV ribbon is a key component in solar panels, and it is an important factor to improve the efficiency and durability of solar panels. The efficiency and durability of solar panels can only be achieved with PV ribbons properly installed in the solar panel. PV ribbon can also improve solar panel production efficiency and reduce scrap rate. The quality of PV ribbons and their welding to solar cells is an important factor in ensuring 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. Among them, the silver-containing welding tape has its own advantages in addition to being expensive:

1) Increase the metallurgical bond between the solder and the metal to be welded. Mechanical strength and electrical 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 weldability and fluidity are improved.

3) The resistivity will be reduced, and the high temperature resistance performance will be improved.

2. The resistance of the ribbon is mainly determined by the size of the ribbon 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 ribbon. Increasing the width or thickness of the ribbon can reduce the resistance of the ribbon. This improvement can play the same role in traditional soldering methods or new low-temperature connection methods such as conductive silver glue or conductive tape connection. However, a ribbon wider than the width of the front electrode will block incident light and cause current loss. We recommend using thicker ribbons without compromising the chip rate.

3. The part of the solar cell covered by the ribbon cannot absorb sunlight. Some ribbon companies have introduced reflective ribbons. The front of the ribbon is silver-plated and rolled into a longitudinal groove-like structure. This structure can be incident on the ribbon. The light is reflected to the inner surface of the glass layer of the module at a certain angle, and is projected back to the surface of the cell after total reflection at the glass-air interface. The captured light allows the module to generate additional power, which could theoretically improve module efficiency by around 2%.

4. Key quality parameters of PV ribbon

The performance indicators of PV ribbons are important in themselves. The type of copper and its purity determine the conductivity of the material and the maximum softness the ribbon can achieve. The flux composition, its cover layer thickness and cover composition affect the quality of the solder joints and thus the durability of the solar panel.

The high elongation of PV ribbons is important to prevent solder joint failures between busbars and interconnecting ribbons, which can occur due to elongation/tension due to temperature oscillations during solar panel operation. The continuous, and sometimes particularly violent, temperature oscillations of the solar panel's lifetime put the solder joints to the test during the lifetime of the solar panel (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 achieve a high level of ribbon softness while maintaining straightness. Getting enough softness and low camber can mean the difference between winning and losing a supply contract. Manufacturers must therefore strive to improve their rolling, annealing, tinning and material handling techniques to meet ever-increasing product performance requirements.

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 lamination process, and the quality control of the welding strip production. We need to understand ribbons from all aspects, although the industry may focus more on packaging materials and battery chips.

2. Common Welding Ribbon Specifications

Automatic spool loading tinned copper tape

◆Copper base: imported refined ductile oxygen-free copper/T2 copper, copper content ≥99.99%, conductivity ≥98%

◆The resistivity of copper base: oxygen-free copper≤0.0165Ωmm2/mT2 copper≤0.0172Ωmm2/m

◆Coating composition: 62%Sn36%Pb2%Ag (optional)

◆Coating thickness: single-sided coating 0.01～0.05mm, the coating is uniform, and the surface is bright and smooth.

◆Coating melting point: 179℃

◆Tensile strength: soft state ≥ 25kgf/m㎡ semi-soft state ≥ 30kgf/m㎡

◆Welding strip elongation: soft state ≥ 35% 3/4 soft state ≥ 25% 1/2 soft state ≥ 15%

◆Width error: ±0.1mm

◆Thickness error: Interconnection strip ±0.01mm, Convergence strip ±0.015mm

Lead-containing silver-coated tin-coated copper tape