In this paper a computationally efficient approach to the modeling of a photovoltaic array is presented. It is especially suited for simulating mismatched operating conditions, in which the different modules of the array work at different irradiation levels and temperatures. The model used allows to keep into account parametric tolerances and drifts among the modules. The proposed technique is based on the use of the Lambert W-function, which allows to obtain an explicit relationship between the voltage and the current of any photovoltaic module. The non linear system of equations describing the photovoltaic array is easily solved thanks to the explicit symbolic calculation of the inverse of the Jacobian matrix. The performances of the proposed numerical approach are discussed especially in cases where a deep mismatch affects the photovoltaic array. (C) 2013 Elsevier Ltd. All rights reserved.