This paper aims at providing a performance analysis of a grid connected photovoltaic power plant in Sardinia by investigating on the effective performance ratio of PV installations, with a critical analysis of the whole energetic transformation chain, starting from the incident solar energy, to the DC energy output from the modules and AC energy output from the inverter and transformer. The parameters that can influence the energy production are analyzed in order to find out the critical points in the optimization of the PV system design process. One year measurement and performance analysis of two real-life grid connected PV power plants are presented in the paper, providing up-to-date measurement data, useful to compare the effective energy production of PV plants positioned in different areas of the world. Monthly variability of the performance ratio and its correlation with ambient temperature is also discussed in the paper. (C) 2013 Elsevier Ltd. All rights reserved.