Impact factors in intra-laboratory measurement reproducibility for photovoltaic modules

Xin Huang1, Yuanpang Hao1, Hongmin Han2, Chenhui Nan1, Haixing Tian1, Hong Yang1, He Wang1 1Xi’an Jiaotong University, Xi’an, China /2Center for Metrology and Detection of Luoyang, Luoyang, China

Photovoltaic (PV) module is the core component in PV system. With exposure time increasing, performance of PV module gradually decreases due to aging under composite stress in the field. The residual maximum power output under standard test conditions is one of the most important performance indicators for PV module, which is always estimated using solar simulator in certified or mobile test lab or using portable I-V tracer for on-site measurement followed by a I-V data correction procedure according to IEC 60891. In this regard, measurement uncertainty and measurement reproducibility are two aspects that cannot be ignored in order to ensure residual power estimation being effective. Generally, measurement uncertainty in certified lab is the smallest among the aforementioned three approaches. Moreover, regarding in-field measurement, the determination of uncertainty for solar module and its variation effect on module power estimation have been well documented. However, only few studies are available in terms of measurement reproducibility for PV modules, especially for impact factors of measurement reproducibility. In the present work, measurement reproducibility for PV modules was studied both theoretically and experimentally. Measurement reproducibility for PV modules was estimated with the extreme value method for the first time. This method can be well applied even if the number of I-V measurement is very limited. In addition, the effect of irradiance and temperature on measurement reproducibility was also studied. It is found that reproducibility of ISC is the smallest, followed by that of Imp, FF, VOC and Pmax, and reproducibility with respect to Vmp is the largest. The size order is basically the same under different irradiance and temperature conditions. Moreover, reproducibility of VOC and Pmax increase when irradiance and temperature increase. This work can shed some light on intra-laboratory measurement reproducibility determination and power output decay estimation for PV modules.