Challenges in photovoltaic parameter identification under mismatching conditions

When connecting a few solar cells in series to create a photovoltaic (PV) module, even the smallest discrepancies between them are enough to create mismatch losses. Sometimes this mismatch is mainly due to the non–uniformity of the operating conditions associated with variations in irradiance or cell temperature. However, even under uniform conditions, the unavoidable dispersion of the intrinsic parameters of the cells, due to degradation and aging effects, could be a cause of mismatch because each cell, sharing the same value of current, will be polarized at a slightly different voltage. For accounting for the presence of mismatch in a series of PV cells a Double - Single Diode Model (D-SDM) is introduced in this paper. The parameters between the resulting two SDMs circuits were related to obtaining reliable and coherent characterization for different operating conditions. A robust procedure is developed for estimating its parameters and evolutionary algorithms are employed to solve the optimization problem. The proposed methodology was also validated using experimental data from a single cell of the same type as the module.