This paper presents a simple and successful method for evaluating the series resistance, the ideality factor, the saturation current and the shunt conductance in illuminated solar cells. The approach involves the use of an auxiliary function and a computer-fitting routine. The validity of this method has been confirmed by the way of current-voltage measurements of a commercial silicon solar cell, a module and a plastic solar cell. (c) 2006 Elsevier Ltd. All rights reserved.