Comparative Performance analysis of different PV plants in Italy

Photovoltaic (PV) systems energy yield is heavily affected by several factors such as: weather conditions, soiling, ageing, modules cooling, and many others. Performance Ratio (PR) is a relevant performance metric for PV systems and its value changes on a daily and seasonal basis, especially because of the modules temperature variation. In this framework, different PR formulations are known in literature aimed at applying a temperature correction to mitigate seasonal variations. However, different formulas of PR might lead to unfair PV plants performance comparison. In this paper, three different PR formulas from standards are considered and compared on two different cases study with the aim of investigating the peculiarities of 22 PV plants in Italy, evaluating both their geographical and installation typology effects on the computed PR. Besides, performance of a test plant located at Politecnico di Milano, from 2017 to 2020 has been monitored and assessed. The comparison of different PR calculations aims at evaluating weather effect across the years. Neglecting anomalies and missing data, in the 4 years observed, the standard PR goes from 0.70 to 0.88; the Temperature Corrected PR goes from 0.76 to 0.90 and the Weather Corrected PR goes from 0.78 to 0.92.