Long-term Degradation Rate of Photovoltaic Modules: A Meta-analysis

A critical factor in determining the ecological and economic benefits of photovoltaic investments is the projected lifespan of the installed photovoltaic modules. Therefore, a well-founded estimate of the decline in power output over an extended period is essential in assessing whether an installation under a specific set of conditions can meet performance expectations. This power decline, commonly referred to as degradation rate, is dependent on multiple factors that result in a large heterogeneity of contingency factors determining the degradation rate. To derive the summarized effect of all reported degradation rates of outdoor exposed photovoltaic modules across the academic literature and explain the large differences observed, we conducted a meta-regression analysis of 85 primary studies reporting 699 observations for the degradation rate. Using a wide set of moderator variables, including geographical characteristics, installation differences, methodological differences, and publication characteristics, the analysis revealed a median degradation rate of 0.94 %/year, with the cell technology, mounting location, and methodological differences being the main drivers of heterogeneity in reported degradation rate observations. Interestingly, technological advances have not been found to systematically reduce reported degradation rates. Finally, we use the meta-regression results to derive an implied degradation rate under best practice conditions and found the widely employed crystalline silicon modules degrade at rates of 0.39 % to 1.44 %/year. In contrast, thin-film modules exhibit degradation rates twice as high at around 2 %/year. Consequently, the empirical literature suggests a projected lifespan of 51 years under the most favorable conditions, i.e., a well-ventilated installation of crystalline silicon modules mounted in cold climate conditions. The results of this study can guide future research as we summarize the status quo of the academic evidence on photovoltaic degradation. Moreover, the aggregated degradations can serve as a benchmark for future photovoltaic investment decisions.