A comprehensive mathematical model for the planar solid oxide fuel cell (SOFC) stack is presented. The model couples the intricate interdependency among the ionic conduction, electronic conduction, gas transport and the electrochemical reaction and takes into account the contact resistance between the electrode and interconnect rib and the dependence of the effective electrode properties on the microstructure parameters of the porous electrode. The validity of the mathematical model is demonstrated by the excellent agreement between the numerical and experimental I-V curves. Based on a standard set of model parameters, the cell performance is examined by systematically varying the rib width, contact resistance, fuel composition electrode properties and the pitch width. The results show conclusively that the cell output depends strongly on the rib width and a suitable choice of the rib width is important for realizing the potential of a SOFC stack. The optimal rib width is only sensitive to the contact resistance and the pitch width, but the optimal results for the anode and cathode ribs are quite different. Both the optimal anode and cathode rib widths depend linearly on the contact resistance and the pitch width and the parameters for the linearity are given. (C) 2012 Elsevier B.V. All rights reserved.