This work aims to study the impact of different models for the evaluation of the efficiency of a double axis PV tracking system on the monthly probability distribution function of the AC power. Two components of the global efficiency are analysed, that is: the effect of PV cells temperature on the module efficiency and the DC/AC converter efficiency. In particular, the temperature efficiency model combines basic parameters characterizing the array, with the local monthly average temperature and the monthly clearness index to yield a monthly average efficiency. The simulation results are compared with experimental data related to a 9.6 W-p PV plant installed in ENEA research centre located in Portici, Naples (Italy). The tuning of the model is performed by both system measurements and environmental data. (C) 2012 Elsevier Ltd. All rights reserved.