Study of the Twelve Busbar Technology and the Stress-Induced Degradation within the Solar Modules

Abstract

To achieve cost reduction and efficiency increase of module products, the multi-busbar technology has recently been applied in photovoltaic crystalline silicon modules. Compared with the current five busbar modules, the multi-busbar modules use round ribbons to reduce the resistance loss and increase the secondary utilization of the light on the surface of the ribbon, thereby increasing the power output of modules. However, the use of multi-busbar technology requires redesign of the cell pattern, and thicker solder ribbons may probably lead to more degradation due to inner stress. This stress-induced degradation of the twelve busbar modules was investigated by thermal cycling test and electroluminescence test. The test results demonstrate that by increasing the thickness of EVA, the cracking of the cells caused by the stress during the thermal cycle can be effectively reduced. Our twelve busbar modules exhibited good reliability in the damp heat and UV sequence tests. Introduction Multi-busbar technology is an effective means to increase the output power of the module due to the reduction of the silver paste consumption during cell fabrication[1], decrease of the current loss [2-3] as well as increase of the secondary utilization of light. In recent years, it has received widespread attention in the PV industry [4-6]. Unlike conventional flat ribbons, the MBB technology typically uses round ribbons that are typically thicker than conventional flat ones, which requires adjustment and optimization of the corresponding material and process. To ensure the amount of power generated by the module throughout its lifetime, special attention needs to be paid to the power degradation and reliability of the module during outdoor applications. The modules are affected by the complex environment during outdoor use, and the degradation inducements are also diverse [7-11]. At present, most of the large domestic power stations are distributed in the northwestern region, with large temperature difference between day and night and strong ultraviolet radiations. Therefore, modules should also be designed and verified for this environment. In this paper, to improve the output power of our products, we studied the power gain of the twelve busbar (12BB) technology compared with the conventional five busbar one. We also evaluated the reliability of the welding between the interconnecting ribbon and the cell. The thermal cycle and electroluminescence (EL) tests were used to study the stress-induced degradation of the 12BB module. The effect of thicker EVA encapsulant film on reducing the stress-induced degradation was investigated. The EL results are consistent with the output power degradation of the module. The damp heat and ultraviolet sequence tests demonstrate that the 12BB modules possess good weathering resistance. Experimental Section The 12BB and 5BB cells were fabricated using silicon wafers of the same quality. The silicon wafers were all made of the same processing materials and parameters for texturing, diffusion, etching and 2nd International Conference on Electrical and Electronic Engineering (EEE 2019) Copyright © 2019, the Authors. Published by Atlantis Press. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). Advances in Engineering Research, volume 185