Assessing the suitability of I-V curve translation at varying irradiance and temperature range

Abstract

Discrepancies in operating conditions while measuring I-V characteristics for a photovoltaic (PV) module produces inadequacies in further analysis and modelling. IEC 60891 presents a straightforward approach for translating I-V curves from measured to reference data points. The complexity arises while extracting parameters such as series resistance (RS), the diode thermal voltage (a) and curve correction factor (k), when the requirements of IEC 60891 are not adequately met. Accuracy of extracting unknown parameters through a modified IEC 60891 procedure 2, presented in literature for curve translation, is investigated for varying ranges of irradiance and temperature in this research work. Optimization tool is employed to determine optimal value of RS and k, deviating from the predefined incremental step change methodology. Experimentally measured I-V curves for a bifacial module were utilized for curve translation and subsequent error estimation. The errors in translated values for VOC, ISC, VMP, IMP and PMAX were estimated to validate the applicability of the modified IEC 60891–2 procedure. Results showed that least error was obtained for PMAX as well as VOC values (∼0%) for all ranges of irradiation, however, the errors increased for ISC, IMP and VMP (1%-9%) for large variations in irradiance and temperature conditions (>300 W/m2).