The first Italian BIPV project: Case study and long-term performance analysis

The estimation of long-term performances of PV systems is a crucial factor for properly assessing the energy and the cost of PV electricity and thus the cost effectiveness of different technologies. This type of prediction is often based on accelerated ageing and tests in indoor condition. However, the combination of different phenomena, such as the mean solar radiation available on the site, the presence of dust, the shadowing or UV radiation over long-outdoor exposure, affect in different ways the real performance of the PV systems.This paper presents a detailed assessment of the testing campaign on the pilot PV plant at the Politecnico di Milano, which underwent 13 years of continuous operation; such period is particularly representative because it can be considered as about half of the supposed lifetime cycle of a photovoltaic system which is usually taken into account for technical-economic evaluations.The results obtained show that the PV plant analyzed didn't present a significant decrease in long-term performance: the measured PR decay is equal to 0.37%/year. In addition, the visual inspection and IR analysis showed that no PV modules are affected by serious damage. This result is due to a good system design during the preliminary stage, high-quality components and also the back ventilation of the modules, which avoids overheating in the warmer periods of the year.Finally, an economic analysis was carried out - based on real historical data - which makes the economic evaluation more reliable.