Degradation analysis of a-Si, (HIT) hetro-junction intrinsic thin layer silicon and m-C-Si solar photovoltaic technologies under outdoor conditions

Understanding degradation mechanism is of utmost importance for long term reliability of photovoltaic technology. In the present study, degradation analysis of three different photovoltaic technology modules namely a-Si (amorphous single junction silicon), HIT (hetro-junction intrinsic thin layer silicon) and m-C-Si (multi-crystalline silicon) is carried out after 28 months of outdoor exposure at Solar Energy Centre, India. A comprehensive test campaign is conducted by visual inspection, thermal imaging and current-voltage characteristic measurements. The soiling of glass is observed in all modules, wavy pattern in back sheet is seen only in a-Si array modules. 50% of m-C-Si modules showed oxidation of silver front grid metallization fingers and antireflective coating at multiple places. Degradation of modules is assessed by measuring characteristic parameters at standard test conditions, before and after outdoor exposure using sun-simulator. The average peak power decay per year is found to be 6.4%, 0.5%, 0.36% in a-Si, m-C-Si and HIT modules respectively. Degradation in each technology array is also calculated analytically and is found to be 5.7 ± 2.5%, 0.51 ± 0.017%, 0.31 ± 0.016% in a-Si, m-C-Si and HIT modules respectively which is in good agreement with experimentally measured results. The study will be useful in further understanding of degradation mechanism under Indian climatic conditions.