This paper presents an assessment of the reliability of neutral point clamped (NPC) based photovoltaic (PV) systems using a mission profile. The study focuses on the two types of fragile components in these systems, namely the insulated-gate bipolar transistors (IGBTs) and the DC Al electrolytic capacitors. Additionally, the effects of power degradation due to the aging of PV panel and the over-temperature derating characteristics of the NPC inverter are considered to make the lifetime evaluation more realistic. The evaluation is demonstrated using a study case of a 225 kW PV system based on actual mission profile and commercial components. The study results indicate that careful consideration of these factors is crucial to improve the design and operation of NPC inveter-based PV systems. This paper provides valuable insights into the evaluation of the reliability of NPC inverter-based PV systems.