Behavior of Interconnect-Failed PV Modules Under Standard Test Conditions and Actual Operation Conditions

Comparisons of indoor measurements under standard test conditions (STC) and outdoor measurements under actual operation conditions of ten-year-used interconnect-failed PV modules were described. In the indoor measurements under STC, no sample modules showed the output power degradation of more than 20% from the rated power. In the outdoor measurements of the sample modules, the open-circuit voltage decreased in a discrete value with a half volt of the rated open-circuit voltage when the module temperature is elevated. The discrete voltage change is due to the interconnect disconnections, and the disconnection failures have module-temperature-dependent characteristics. Even though the output of the failed module drastically degraded under actual operation conditions, the performance evaluation under STC did not show the degradation judged as the failed module. It means the possibility that the failed modules pass the module performance warranty criteria if only use the STC measurements. To avoid the oversights of the module performance, it is important to develop the certified on-site diagnosis methods, which can properly evaluate the performance under the actual operation conditions.