PV panels R s parasitic resistance degradation estimation by means of the MPPT controller modified operation: the M-factor calculation

This Letter describes a method to quantify online and in real-time, the level of degrading of the series parasitic resistance R s of a photovoltaic (PV) panel. This method aims to obtain the herein proposed M-factor, which results from the calculation of the slopes of the I–V curve in the boundaries of its maximum power-point. For this purpose, the slight modification of the maximum power-point tracker controller’ perturb and observe algorithm is required. This procedure can be easily integrated into its firmware with no additional costs. The M-factor calculation is performed instantaneously and since no disconnection is required, no significant power losses are produced.