Analysis of the outdoor performance and efficiency of two grid connected photovoltaic systems in northern Italy

This paper analyzes and compares the actual performance of two grid connected photovoltaic plants, which are of similar size but based on different modules technologies. The facilities are located on the roofs of two buildings of Area Science Park in the site of synchrotron ELETTRA in Basovizza (Trieste). The first system is equipped with modules of mono crystalline silicon wafer surrounded by ultra-thin amorphous silicon layers (hetero-junction with intrinsic thin layer), facing south and tilted at 30°, the second is equipped with mono crystalline silicon modules oriented 35° west and inclined at 10°. The set of data analyzed in this paper has been systematically acquired from October 15th 2011 to October 14th 2012 by means of a dedicated monitoring system. The aim of this study is to analyze the actual performances of the plants and their yearlong evolution, separating the effects of the variability of environmental conditions from those due to the variability of the performance of panels and electrical components. Particular attention is given to the influence that irradiance and temperature have on the efficiency of the system. An analysis methodology was applied to appropriately filter, classify and normalize the data in order to identify the modules temperature coefficients as a function of irradiance and to compare their actual efficiency with those declared by the manufacturer. Acquired data and mathematical correlations will allow the development of accurate simulation models, useful for assessing the actual profitability of similar installations. The latter can be obtained through the main performance indices of the systems that are calculated and reported in this paper for the period of observation.