In this study, a novel approach is proposed to determine the maximum amount of exergy from the sun when applied to a conventional photovoltaic (PV) system in order to formulate its exergy efficiency. The variations of exergy efficiency are investigated for two cases using actual experimental data obtained from an installed PV system in Turkey. A new computer program is written in the Matlab-Simulink software environment for data analysis. Subsequently, all the results are provided for the purpose of comparison. The results provided in the study are expected to be beneficial for researchers, designers and engineers working on PV energy systems and their performance assessment. (C) 2012 Elsevier Ltd. All rights reserved.