The alleged reliability has led the longest warranty period for Photovoltaic (PV) modules up to 20–25 years; it becomes possible after understanding the failure mode and degradation analysis of PV module. Failure mode decreases the performance of the PV module throughout the long-term outdoor exposure. The main objective of the present study is to identify the failure mechanism and failure mode of solar PV modules and their impact on degradation in operating conditions. Assessment of previous studies on rate indicates the highest performance losses at initial stage of outdoor exposure and a degradation drop-off of 0.014% per year. In this context, risk priority number (RPN) analysis is carried out to identify the severity of the failure mode, which affect the system performance for c-Si technologies. However, hot spot and de-lamination are degradation modes related to safety issue with lower value of RPN <50. •Failure mechanism and failure mode of solar PV modules in real outdoor conditions.•Studies on the mono-crystalline PV modules over a period of 25 years are considered to identify defects and failure modes.•Impact of PV module defects and failure modes on its degradation is presented.•Risk priority number (RPN) analysis for identifying the severity of the PV failure mode.