This work represents the Photovoltaic section of the European Project PERSIL, which includes also the study of solar thermal plants. The activity is twofold: the results of 1-year monitoring and checking of thirteen PV systems; the consequent guidelines for the design, installation and maintenance of grid connected PV systems. For accurate estimation of the energy production a two-year analysis of solar radiation has been conducted on the basis of pyranometer measurements in all the Project locations. The checking of energy performance has been carried out by a suitable improvement of a conventional method, that includes the assessment of the energy availability. The corresponding results are excellent for three PV plants, whereas they are strongly negative for five old PV plants which exhibit poor availability (62-78%). The remaining plants behave with acceptable performance ratios (0.65-0.78). Within the guidelines for design, the optimum coupling array/inverter and the related protections have been discussed in detail. About the guidelines for installation, the PV module/inverter cooling, the electric cables and enclosures have been dealt with. Then, concerning the guidelines for maintenance, the main items are the energy production assessment, the glass dirt checking and the maintenance of motors in sun-trackers. Finally, all these guidelines help to maximize the energy availability. (C) 2013 Elsevier Ltd. All rights reserved.