Measurement Repeatability of Crystalline Silicon Photovoltaic Modules in the Field

Obtaining high-quality repeatability data is the basis for improving measurement precision. Due to the inherent instantaneous fluctuation nature of field test conditions, obtaining high quality repeatability measurement results of photovoltaic (PV) modules in the field is still challenging. In this paper, firstly, we defined repeatability of PV modules measurement in the field, including repeatability and relative repeatability of measured and standard test conditions (STC)-corrected electrical parameters for fielded PV modules. Because STC is quite difficult to directly obtain outdoors, the correction procedure 4 in IEC 60891:2021 is used to obtain module STC characteristics. Then, the effect of the correction procedure on repeatability of electrical parameters of PV modules in the field was studied. The results show that repeatability of electrical parameters is changed before and after correction process. The variation reason was revealed by the established repeatability error propagation model. It is remarkable that there exist module maximum power point offsets before and after module characteristics correction. Moreover, the covariance terms contribute significantly to repeatability variation for fielded PV modules. Finally, the effect of field test conditions variation on repeatability of electrical parameters of PV modules was studied. The relative repeatability precision of module STC maximum power between field and indoor measurements was also compared. It is found that there is a greater probability to obtain indoor-level repeatability results within 0.7-1.0 kW/m2 irradiance ranges (3.29%-5.04%) than that within 0.3-0.7 kW/m2 irradiance ranges (0.47%-2.90%) for PV measurements in the field. The obtained results in this paper can provide new insights into precise performance measurement of PV modules under dynamic outdoor environmental conditions.