This work presents a novel analytical approximation of the effect of inter-row shading on large photovoltaic (PV) arrays. Computation time is reduced orders of magnitude relative to full numerical simulations, allowing this method to be used in annual production estimation software – for instance, it is currently implemented in the National Renewable Energy Laboratory’s System Advisor Model program. A further advantage of the analytical approach is that, unlike numerical simulations, computation time does not increase with the size of the PV installation. Comparisons with full I–V curve simulations indicate that this simplified approach has typical error of 1% over multiple module fill factor, shade extent and shade opacity assumptions. Maximum error of 2-6% was found for simulations of crystalline silicon modules. Comparisons with experimental results show good agreement between the experiment and the model over a range of operating conditions, and intercomparison with prior modeling methods indicates a spread of possible model results, depending on model assumptions.