Remote diagnosis of residential PV systems become important in reducing the Operation & Maintenance cost. In this study, we have developed Operating Performance Index Method (OPI method) which can remotely detect the output power reduction of the PV systems. This method can distinguish between the output reduction due to a failure and a shading by using the configuration data and power output of PV systems, ambient temperature, solar radiation, and wind speed. A failure detection experiment was also conducted by using the 4kW system. This system consists of 24 modules (8 series connected modules in the strings and 3 parallel strings) and has output reduction due to the shading during winter morning and evening. One of the modules in the experimental system was bypassed in September 2016 and output reduction about 7% was successfully detected in October 2016.
