A novel procedure for identifying the parameters of the single-diode model and the operating conditions of a photovoltaic module from measured current–voltage curves

Photovoltaic (PV) module measured current–voltage curves together with the mathematical single-diode model are potential tools for PV system condition monitoring. Changes in model parameters can reveal module degradation and aging. However, all the parameter values change with varying operating irradiance and temperature, so they should also be identified. Unfortunately, useful operating condition measurements are rarely available in PV power plants. Thus, it is necessary to identify both operating conditions and model parameters directly from measured current–voltage curves. Only one such method has been reported in literature, however, using approximate explicit equations. The present work proposes a novel fitting procedure that identifies both single-diode model parameters and PV module temperature and irradiance utilizing an iterative method instead of approximate equations, which guarantees accurate results. The procedure enables degradation and aging analyses using only the internal electrical current–voltage curve measurements of the inverter. The results showed that the identified irradiance and temperature accurately reproduced the measured ones in all outdoor conditions. The stable identification of other single-diode model parameters, of which series resistance is especially suitable for detecting aging, confirmed the functionality of the procedure for condition monitoring.