Multi-pronged degradation analysis of a photovoltaic power plant after 9.5 years of operation under hot desert climatic conditions

Long-term reliability assessment of photovoltaic (PV) modules is key to ensuring the economic viability of PV systems. This paper presents a multi-pronged performance degradation analysis of a 62.1 kWp solar PV power plant after 9.5 years of operation. For this purpose, various diagnosis techniques, namely, visual inspection, infrared thermography (IR), ultraviolet fluorescence (UVFL) and current-voltage (I-V) characterization, have been performed to evaluate the performance and degradation of the solar PV power plant. The visual characterization results show that the PV strings are affected by different mechanisms with different degrees of occurrences. The degradation mechanisms observed and the level of occurrence among the modules were found to be, encapsulant discolouration (100%), degraded frame adhesive (57%), degraded junction box adhesive (39%), snail trails (30%), burn marks (3%), cell cracks (2%) and delamination (0.4%). Although discolouration of the encapsulant was the most common possible degradation mechanism observed, the main causes of the power loss were snail trails and cracks in the PV cells. Furthermore, the IR thermography and UVFL analysis provided better understanding on snail trails phenomenon and crack mechanism on the affected PV modules. Besides imaging techniques, to assess the electrical performance of the system, we performed current-voltage (I-V) and power-voltage (P-V) characterization of the entire PV plant from which the degradation rates of the electrical parameters were determined. Our results show that the degradation rates for the maximum power and the fill factor are 0.84%/year and 0.66%/year, respectively, over the operating period of the installation. The estimated maximum power degradation rate for this installation could be considered as a realistic degradation rate for PV modules installed in harsh and hot desert climatic conditions. Additionally, our work has raised doubts about the validity of the warranties proposed by the manufacturers.