This paper presents a simple accurate model that allows calculating the shading power losses in photovoltaic generators in a fast, easy to implement way. Calculated losses for different generators and shading scenarios are compared to those obtained with a detailed model based on solving the whole current voltage curve of the generators. Results show a good agreement between the proposed model and the detailed model. The proposed model is useful for the calculation of the instantaneous power losses and also gives good results in the calculation of the energy yield, requiring less information as input than other detailed models and requiring low computational effort. (C) 2013 Elsevier Ltd. All rights reserved.