Salvatore Guastella* 22nd European Photovoltaic Solar Energy Conference and Exhibition Milano 3-7 Settembre 2007 *CESI RICERCA The work deals with an evaluation of operational data of selected Italian PV plants, to investigate their performance through the lifetime. As the number of PV plant installations in Italy is quickly increasing, mainly due to the national Feed-in tariffs Programme, several new PV operators (designers, architects, investors, ..) are asking for the performance and lifetime of these plants, in order to evaluate their-own technical and economic interest in this technology. Moreover governmental decision makers and electric grid managers are demanding for the quality, through the years, of PV systems operating in connection to the grid. In this context, the evaluation of PV plant data can provide an incomparable possibility to increase the knowledge on the behaviour of PV plants trough the time, according to the installation site, the adopted components and the design. Performance evaluation of more than 40 PV plants installed in Italy and experience gained on tests and management of different PV plants resulted to demonstrate a good reliability of PV technology through the years and at different locations. Modules resulted the most reliable component of PV plants and their power degradation has been detect to be less than the value guaranteed by manufacturers. In the light of the above results, it can be assess that a well designed and maintained PV plant can result in a lifetime even longer than 30 years without remarkable performance degradation