FMEA Based Degradation Rate Evaluation to Study Impact of Different Failure Modes as Function of Mission Profiles

Crystalline silicon modules were, are and will be the dominant solar cell technology. Associated with that different cell technologies (e.g. Al-BSF, PERC, TOPCon, HTJ, IBC) show different behaviors against outdoor stressors. Furthermore, the PV module encapsulation system (such as front cover, encapsulation material, rear cover, and edge seal) will additionally influence the long-term reliability of the PV system. Therefore, it is important to understand the most relevant factors and clarify expectations. Costs are the main driver to reduce material consumption and increase efficiency in all steps of the value chain, including cell efficiencies. Business case for a particular system is made from system designs (energy yield), assumed annual degradation rates, building cost (CAPEX), and operation costs over the project live time (OPEX). The work laid out in this contribution focuses on the technical risks associated with assumed degradation rates for financial modeling and how to address the risk with proper testing. A Failure Mode and Effects Analysis (FMEA) study was undertaken to identify, prioritize, and rate different major field observations with the aim to achieve a deeper understanding of the real impact on degradation rates. Different types of pillars are derived to further support testing development with respect to the relevant mission profile (MP) of the PV module/system. As pillars the following categories were used: Design & Quality issues, MP-linked degradation mode (hot desert, temperate climate, etc.), and safety aspects. The reference point for this study is the warranty given “allowed maximal” degradation rates by the manufacturers. If on a contract base other warranty terms are used is outside of the scope of this work but could be adjusted to it. The major and most relevant topics identified were related to cell metallization issues (e.g. finger interruptions on MBB-design cells), interconnection ribbon fatigue, including a detachment of ribbons from cross connectors, and change in polymeric materials (discolorations).