For organic photovoltaics (OPVs) to contribute significantly to energy generation, they need to be scaled to large areas much like all organic electronics. So it is timely for the need and development of a specific model to describe the electrical behaviors related to the size effects and cell interconnections. We report here on the equivalent circuit models for a high-performance series-connected OPV module based on a polymer:fullerene bulkheterojunction formulation. We examine the validity of the effective single cell methodology in the conventional framework, and suggest a modified model that includes the net series resistance and additional parasitic leakage conductions. The photocurrent is found to follow the diffusionlimited voltage dependence, for which an empirical treatment enables an improved reproduction of the measurement near the short-circuit point.