Two- and three-diode models for solar cells: The impact of series resistance repositioning on performance and accuracy

Accurate modeling of solar cells remains challenging due to the strong nonlinearity of their current–voltage characteristics and the trade-off between structural complexity and numerical robustness. Although classical equivalent-circuit formulations such as the Single-Diode (SDM), Double-Diode (DDM), and Three-Diode Models (TDM) are widely used, increasing the number of diodes does not necessarily yield proportional improvements in accuracy. This study addresses this limitation by proposing structurally modified DDM and TDM configurations in which the series resistance is repositioned into a common diode branch, providing a physically consistent representation of collective resistive losses without increasing the number of parameters or computational burden. An iterative numerical procedure is additionally developed to ensure stable and efficient solution of the resulting nonlinear current–voltage equation over the full operating range. The proposed models are validated using benchmark datasets (RTC France solar cell and Photowatt-PWP 201 solar module) and experimentally verified under real outdoor conditions on a photovoltaic installation in Niš, Serbia. The results demonstrate consistent accuracy improvements over classical DDM/TDM structures, with Root Mean Square Error (RMSE) reductions of 21.18% (to 5.8267 × 10−4) for the RTC France solar cell and 34.06% (to 1.4496 × 10−3) for the Photowatt-PWP 201 module. Notably, the proposed configuration yields enhanced agreement in the high-current region and around the maximum power point, where resistive effects are dominant and modeling precision is critical for system-level applications. By combining physically motivated circuit restructuring with numerical robustness, the proposed approach advances equivalent-circuit PV modeling and provides a practically applicable framework for performance prediction, optimization, and control of photovoltaic systems. The MATLAB code for calculating the current of the modified DDM circuit, which was implemented, is also provided to enable reproducibility of the results.