Dependence of Series Resistance on Ideality Factor and Shunt Resistance in Online Photovoltaic Module Parametric Identification

Ageing of photovoltaic (PV) modules can be comprehensively detected by investigating measured current–voltage curves. The curves can be subjected to fitting the single-diode model describing the operation of a PV cell. The model parameters provide numerical information of the condition of the PV cells. Especially, series resistance is a specific indicator for ageing, whence it should be reliably identified. As the parameters depend also on the selected identification procedure and the operating conditions, those effects should be distinguished. Therein, a problem is the strong interconnection of the parameters: variation in one parameter affects the others too. Particularly, values of the ideality factor and the series and shunt resistances depend on each other. This must be taken into account before drawing diagnostical conclusions. At practical PV applications, only such identification procedures that can reproduce the operating conditions are of interest. However, the effects of variations of ideality factor and shunt resistance on the series resistance when using such procedures are unclear. This article addresses this issue by investigating the effects of these parameters on the series resistance by using two identification procedures that identify also the operating conditions. The results provide guidance for online condition monitoring of PV systems.