1、 The impact of photovoltaic ribbon on modules

PV ribbon is an important component of every mainstream solar panel, used to interconnect solar cells and provide connections to junction boxes. The PV solder strip is a tinned copper strip with a width of 1-6mm and a thickness of 0.08-0.5mm, with a thickness of 10-30 μ M-thick flux coating.

There are two forms of application of PV solder strips in photovoltaic modules: interconnect strips or busbars and PV busbars. Both are required in typical silicon solar cells. The interconnect strip is directly soldered onto the silicon crystal to connect the solar cells in the solar panel to each other. The interconnect belt carries the current generated by the solar cell to the PV busbar. The PV busbar is a hot-dip tinned copper conductor installed around the periphery of the solar panel. The PV busbar connects the interconnect strip to the junction box. Thin film solar panels generally only require a busbar.

PV ribbon is a key component in solar panels and an important factor in improving the efficiency and durability of solar panels. The high efficiency and durability of solar panels can only be achieved with high-quality PV solder strips installed appropriately in the solar panel. High quality PV solder strips can also improve the production efficiency of solar panels and reduce scrap rates. The quality of PV ribbon and its welding to solar cells are important factors 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, silver containing solder strips have their own advantages besides being expensive:

1) Increase the metallurgical bonding between solder and the welded metal. The mechanical strength and conductivity will be better after welding.

2) After adding silver, the melting point of ternary alloys is slightly lower than that of binary alloys, and their weldability and fluidity are improved

3) The electrical resistivity will decrease and the high-temperature resistance will improve.

2. The resistance of the solder strip is mainly determined by the size specifications of the solder strip itself and the material of the copper substrate. The composition of the surface tin coating will not significantly affect the resistance of the solder strip. Increasing the width or thickness of the solder strip can reduce its resistance. This improvement can have the same effect on both traditional welding methods and new low-temperature connection methods such as conductive silver adhesive or conductive tape connections. But welding strips wider than the width of the front electrode will block the incident light, causing current loss. We recommend using thicker solder strips without affecting the fragmentation rate.

3. The part of the solar cell covered by the solder strip cannot absorb sunlight. Some solder strip companies have introduced reflective solder strips. The front of the solder strip is silver plated and extruded into a longitudinal groove like structure, which can reflect the light incident on the solder strip at a certain angle to the inner surface of the glass layer of the component. After total reflection at the glass air interface, it is projected back onto the surface of the battery. The captured light energy generates additional power for the component, theoretically improving the efficiency of the component by about 2%.

4. Key quality parameters of PV welding strips

The performance indicators of PV solder strips are important in themselves. The type and purity of copper determine the conductivity of the material and the greater flexibility that the solder strip can achieve. The composition of the flux, its coverage layer thickness, and coverage components affect the quality of the solder joints, thus affecting the durability of solar panels.

The high extensibility of PV solder strips is important for preventing solder joint failures between busbars and interconnect solder strips, which may occur due to the extension/tension caused by temperature oscillation changes during the operation of solar panels. During the lifespan of solar panels, continuous and sometimes particularly intense temperature oscillations occur every day, causing solder joints to be tested during the lifespan of the solar panel (averaging 25 years).

The two crucial parameters for most PV ribbon manufacturers are curvature and yield strength. Many PV ribbon manufacturers find it difficult to achieve high levels of ribbon flexibility while ensuring its straightness. Obtaining sufficient flexibility and low curvature 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 increasing demands of product performance indicators.

So, the impact of welding strips on the power generation of components is not only limited to the design materials of the welding strips themselves, but also includes the selection of welding strips, the lamination process, and the quality control of welding strip production. It is necessary to understand solder strips from various aspects, although the industry may focus more on packaging materials and battery cells.

2、 Common welding strip specifications

Automatic spool assembly with tin coated copper strip

◆ Copper based: Made of imported refined toughness oxygen free copper/T2 purple copper, with a copper content of ≥ 99.99% and a conductivity of ≥ 98%

◆ Copper based resistivity: Oxygen free copper ≤ 0.0165 Ω mm2/mT2 Purple copper ≤ 0.0172 Ω mm2/m

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

◆ Coating thickness: Single sided coating of 0.01-0.05mm, uniform coating, bright and flat surface.

◆ Coating melting point: 179 ℃

◆ Tensile strength: Soft state ≥ 25kgf/m ㎡ Semi soft state ≥ 30kgf/m ㎡

◆ Elongation rate of solder strip: Soft state ≥ 35% 3/4 Soft state ≥ 25% 1/2 Soft state ≥ 15%

Width error: ± 0.1mm

◆ Thickness error: ± 0.01mm for interconnect strips and ± 0.015mm for busbars

Lead and silver coated tin copper strip

◆ Coating composition: 63% Sn36% P2% Ag (optional)

Lead coated tin copper strip

◆ Coating composition: 63% Sn37% Pb, 603% Sn40% Pb (optional)

◆ Coating thickness: Single sided coating of 0.01-0.05mm, uniform coating, bright and flat surface.

◆ Coating melting point: 183 ℃, 190 ℃

Lead free environmentally friendly tinned copper strip

◆ Coating composition: 96.5% Sn3.0Ag0.5% Cu, 96.5% Sn3.5Ag (optional)

◆ Coating thickness: Single sided coating of 0.01-0.05mm, uniform coating, bright and flat surface.

◆ Coating melting point: 217 ℃, 221 ℃