Effect of errors in STC maximum power on reliability evaluation and power warranty period determination of photovoltaic modules

Maximum power under standard test conditions (STC) is the core criteria to judge whether photovoltaic (PV) module failure occurs or not. During STC maximum power determination process, errors are unavoidable and the error values are related with test methods. In this work, effect of errors in STC maximum power on module reliability evaluation and power warranty period determination was studied. The error values are set to -5%, -3%, -1%, 0, 1%, 3% and 5%, respectively. The results show that the smaller the error in STC maximum power, the more unreliability the modules. An interesting finding is that for negative errors and positive errors having the same absolute values, the effects of negative errors and positive errors on module reliability variation are different. Furthermore, negative errors have a more significant effect on module reliability variation than positive errors. In addition, relationship among module power warranty period, error in STC maximum power and acceptable module failure ratio is established. It is found that error in STC maximum power plays a major role in power warranty period determination compared with the acceptable module failure ratio. This work is helpful for module stakeholders to understand the importance of error control for module performance evaluation.