This paper deals with the determination of optimum tilt angle and orientation for solar photovoltaic arrays in order to maximize incident solar irradiance exposed on the array, for a specific period of time. The method is extended, by introducing a second objective, i.e. minimization of variance of the produced power, in terms of hourly power generation throughout the given period of time. The proposed method uses both well-established models and data collected from the particular area where the photovoltaic panels will be installed and is built upon four steps. In the first step, the recorded data are used in order to select the most accurate, among several isotropic and anisotropic models that can be found in the literature, for predicting diffuse solar irradiance on inclined surfaces. In the second step, the recorded data and the selected model are used to construct a database that contains the averages and the variances of the hourly global solar irradiance on tilted surfaces over specific periods of time, for various tilt angles and orientations. In the third step, the database of the previous step is utilized to produce meta-models that correlate tilt angle and orientation with mean global irradiance and its variance on tilted surfaces. Finally, an optimization problem is formulated, aiming to determining the optimum values of tilt angle and orientation, taking into account the constraints and limitations of the system. (C) 2010 Elsevier Ltd. All rights reserved.