Annual degradation rates of recent crystalline silicon photovoltaic modules

Long-term reliability and durability of recently installed photovoltaic (PV) systems are currently unclear because they have so far only been operated for short periods. Here, we investigated the quality of six types of recent crystalline silicon PV modules to study the viability of PV systems as dispersed power generation systems under operating conditions connected to an electric power grid. Three indicators were used to estimate the annual degradation rates of the various crystalline silicon PV modules: energy yield, performance ratio, and indoor power. Module performance was assessed both with indoor and outdoor measurements using electric measurements taken over a 3-year period. The trends in the results of the three indicators were almost consistent with each other. Although the performance of the newly installed PV modules decreased by over 2% owing to initial light-induced degradation immediately after installation, little to no degradation was observed in all the PV modules composed of p-type solar cells over a 3-year operation period. However, the PV modules composed of n-type solar cells clearly displayed performance degradation originating from the reduction of open-circuit voltage or potential-induced degradation. The results indicate that a more continuous and detailed outdoor actual investigation is important to study the quality of new, high-efficiency solar cells, such as heterojunction, interdigitated back contact solar cells, and passivated emitter rear cells, which are set to dominate the PV markets in the future. (C) 2017 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.