Influence of degradation in units of PV modules on electric power output of PV system

The time variations and daily integrated amounts of electric power output of a photovoltaic (PV) system for domestic use were calculated for various degradation cases and diurnal insolation patterns. As a result, the electric power output of the PV system was reduced by the degradation of the PV modules in the system. Especially, it was revealed that the existence of only one highly degraded PV module in the PV system, which corresponds to the most extremely imbalanced degradation situation, leads to the serious decrease in the daily integrated amount of the electric power output. Since the specific only one degraded PV module should be found out at an early degradation stage to avoid this large power reduction of the system, the daily integrated amount of electric power output is insufficient as the diagnostic criterion. From the simulation results, it can be concluded that some degradation diagnosis method that can find out a specific degraded single PV module among many sound PV modules is essential to maximize the installation merit of PV systems because this method minimizes the number of PV modules requiring replacement to recover the power reduction caused by the degradation.