Optical degradation of c-Si photovoltaic modules

The optical degradation produced on single-Si and multi-Si photovoltaic modules after 15 years of outdoor operation at the large-scale Delphos ENEA PV plant, located in Manfredonia (South of Italy), was investigated by making comparative optical reflectance measurements on the exposed modules, after their dismounting and cleaning, and on the original, unexposed counterparts. Four different module fabrication technologies were considered: Helios single-Si, Pragma single-Si, Pragma multi-Si and Ansaldo multi-Si. The corresponding PV generators had shown, on a 10-year outdoor operation period, an output power degradation of 11-22% and an output current degradation of 9-14%, depending on the fabrication technology. Siemens multi-Si modules, of recent technology and exposed for 5 years, were taken as reference. The ageing effects on the dismounted and cleaned modules appeared as the discoloration of ARC layer or the formation of stains over the cell surface. They were investigated by measurements of total reflectance under diffuse light and spectral reflectance under direct light in the 300-1100 nm interval, at /spl theta/=10/spl deg/ incidence. All the exposed modules showed an increase ot reflectance under diffuse light, higher for multi-S modules. Measurements under direct light showed a clear decrease of reflectance in the blue region (400-500 nm), due to ARC discoloration, and the consequent leveling of the spectral reflectance behavior.