Annual Degradation Rates of Five Types of Photovoltaic Technologies Over 12 Years

The purpose of this study was to investigate the long-term reliability of various photovoltaic technologies in Japan under humid subtropical climatic conditions. The five investigated technologies were p-type aluminum back surface field (Al-BSF) single-crystalline silicon (p-type Al-BSF sc-Si), p-type Al-BSF multi-crystalline silicon (p-type Al-BSF mc-Si), copper indium gallium (di)selenide (CIGS), hydrogenated amorphous silicon (a-Si:H), and a-Si:H and hydrogenated microcrystalline silicon tandem (a-Si:H/μc-Si:H) photovoltaic modules. The monthly performance ratio (PR) was calculated based on the power outputs of the photovoltaic arrays and global solar irradiance in the same plane as the photovoltaic arrays, which were measured at 10-min intervals over 12 years. The PR was corrected to 25°C (PR_T=25) as defined by the standard test conditions. Furthermore, the power outputs of all the photovoltaic modules were measured by a pulsed solar simulator (indoor flash testing) from 2012 to 2019. The PR and PR_T=25 values showed that the annual degradation rates of the p-type Al-BSF sc-Si, p-type Al-BSF mc-Si, CIGS, a-Si:H/μc-Si:H, and a-Si:H photovoltaic modules were approximately 0.0%/year, 0.2%/year, 1.1%/year, 0.6%/year, and 1.2%/year, respectively, which were consistent with the results of the indoor flash testing. These results indicate that p-type Al-BSF sc-Si and mc-Si photovoltaic modules can show little annual degradation and should retain high, stable power generation performance for over 20 years. In contrast, the higher annual degradation rates of the investigated thin-film photovoltaic technologies suggest that they did not maintain performance of over 90% of the nominal power outputs even for 12 years.