Abstract-- The paper presents a comparison between the operating parameters of grid connected photovoltaic systems with various sun–trackers at different latitudes. A 9.6 kWp double–axis tracking PV plant, installed at ENEA research Centre of Portici (Naples) and a 49 kWp single– axis sun tracking PV plant, sited close to Saluzzo (Cuneo), have been considered. Although the experimental results show a remarkable increment in the performance for the South Italy site ( 30%), due to both the location and the double axis tracker, the North Italy site almost counterbalances this drawback in the economic analysis, since both the installation cost ( 20%) and the operation & maintenance cost ( 30%) are significantly lower. Index Terms – Clear sky model, Mean sky model, PV energy assessment, NPV economic analysis. I. INTRODUCTION Nowadays, both the high amounts of the local feed- in tariff and the decreasing costs of installation boost the PhotoVoltaic (PV) market in Italy up to one thousand megawatt of installed power per year. The best trade-off between available surface, energy performance and cash flows represents a crucial point: it should be achieved by sun-tracking PV systems. This is the reason of the study presented in this paper, in which a comparison between one axis and two axes in the sun- trackers and among two different latitudes has been carried out. The solution with only one rotating axis does not allow to obtain the maximum gain with respect to the fixed installation, but permits the reduction of the Operation & Maintenance (O&M) costs, due to the only one motor instead of the two motors of the double axis tracker. The energy gains can be evaluated as an amount of 20-25% for one axis (vs. fixed installation) and 30- 35% for double axis arrangements in the Italian sites, according to the number of clear days per year. The astronomic coordinates, easily implemented in the control, can be adopted in substitution of the irradiance sensors which, on the other hand, allow to distinguish a clear day from a cloudy day. This paper has been developed within the project “PhotoVoltaic ENergy Assessment” - PVENAS co-funded by Politecnico di Torino and the Public Administration “Regione Piemonte” of Italy. From the radiation calculations the collection gain in sun-tracking systems can achieve, roughly, in Italian sites best figures of 35-40% on yearly basis, with peak values higher than 50% in summer. Furthermore, the installation cost of a sun-tracking system is, obviously, higher than the cost of a fixed system (at least 10%). Finally, the O&M costs per year in sun-tracking systems are within the 1.5-2% of the installation cost with respect to the typical value of 1% for the fixed installation. In the following sections, the clear sky and mean sky models are presented, a procedure for PV energy verification and the related economic analysis are exposed, before the introduction of the experimental results concerning the sun-tracking PV systems. II. CLEAR SKY AND MEAN SKY MODELS The Moon model provides the theoretical instantaneous values of the solar irradiance at clear sky on a surface orientated in any direction [1]. A reference system with the following set of characteristic angles is used: -  solar declination angle, between the Sun-Earth line and the equator plane (positive North); -  solar height, angle between the Sun-Earth line and the horizon plane; -  zenith angle between the Sun-Earth line and the zenith direction ) 2 (      ; -  s azimuth angle between the projection of the Sun- Earth line and the plane at the horizon with South direction (positive West); -  hour angle, between the meridian plane passing through the observer and the meridian plane passing through the Sun (positive East); -  latitude, with respect to the equator (positive North); -  longitude, referred to the Greenwich meridian (positive East). Two angles are needed for defining the plane of PV modules (PV plane) which collects the solar yield: -  is the tilt angle of the PV plane with reference to the horizontal plane; -  PV is the azimuth orientation of the PV plane. Comparison of Operating Parameters in Grid Connected Photovoltaic Systems with Single/Double Sun–Trackers at Different Latitudes A.V. Boicea*, P. Di Leo*, G. Graditi** and F. Spertino* * Politecnico di Torino, Dipartimento di Ingegneria Elettrica, Corso Duca degli Abruzzi 24, Turin, Italy email: filippo.spertino@polito.it **ENEA CR Portici, P.le E. Fermi, 1 - 80055 Portici (Napoli), Italy