Simplified Recovery Process for Resistive Solder Bond (RSB) Hotspots Caused by Poor Soldering of Crystalline Silicon Photovoltaic Modules Using Resin

Abstract

When the thickness of the solar cell wafer and the amount of Ag to be used decreases, it is the best method to recover the power of the module after use at a minimum cost and reuse the module itself. Economic recovery technology can be applied to the power degradation, caused by the resistive solder bond (RSB) hotspot by poor soldering, because the recovery process can be simplified compared to the power loss that is often greater than 30%. This study demonstrated a quick recovery of the RSB hotspot with on-site recovery technology applied with resin and verified the performance and long-term reliability of on-site recovery technology, compared to the factory recovery method, where the back sheet is removed and laminated to recover the module. Both the factory and field recovery methods confirmed recovery results closer to the initial rated power output of the samples. Each sample was degraded by the RSB hotspot to ~62–65% of the initial power output, and the recovery process successfully recovered it to ~96–99%. In on-site recovery, verification of the possible EVA solvothermal swelling, which is the effect of organic solvents contained in the resin on EVA, is essential for verifying the long-term reliability of the recovered module. In this study, the power degradations of the on-site recovered samples after a TC 200 cycle test are −2.14% and −0.95%, respectively, which are within the certification test standard of the new manufacturing module. Existing factory recovery costs not only in the recovery process, but also in a total of 22 stages, such as the transfer of the target module. The largest advantage is that the on-site recovery process can be restarted in the field after only eight stages.

Effect of Solder Flux on Resistive Solder Bond Hotspot Generation in Photovoltaic Module Circuit Process and Restoration of Hotspot Module

“…The module was repaired by first removing the junction box by making a hole in the hotspot from the back of the module using an iron, and then repairing the RSB hotspot by adding flux and additional solder. [ 13 ] There was no additional damage to the existing cells during the repair process, except that the first cells of the third and fourth strings from the left were partially damaged when the junction box was removed. The 370B sample was also repaired in the same way, and the EL image before and after repair is shown in Figure 16 .…”

“…[ 12 ] Hotspots due to the resistive solder bond (RSB) between the interconnect wire (ribbon) and the lower bus bar are the most serious cause of power reduction and failure in PV modules. [ 13 ] Figure 1 depicts actual photographs of RSB hotspots created from the module's front (Figure 1a) and back (Figure 1b). An electric discharge may be generated at high‐resistance intercontacts that carbonize organic materials like the EVA encapsulation and thus cause RBS hotspot formation, as shown in Figure 1.…”

“…Several cases of atypical electrical power degradation in a system‐connected photovoltaic power plant have been identified, resulting in a significant increase in investigations of RSB hotspots. [ 13,14 ] The string‐connection hotspot commonly damages the bypass diode, causing an electrical loss of approximately 30% of the module output power. [ 15,16 ] Inadequate soldering during module production can increase contact resistance, resulting in the formation of RSB hotspots with heated regions, causing damage to the bypass diodes.…”

“…The RSB hotspots have an impact on overall operation, and in extreme cases, cell encapsulation, joints, metal contact, or the glass cover might break, resulting in module degradation. [ 13–16 ] Therefore, the RSB hotspot formation should be investigated and addressed.…”