PV plant underperformance could be attributed to different reasons. Module’s underperformance stands out in this group. To maximize energy production and the long-term performance of PV systems it is crucial to identify underperformance issues as early as possible. The outcomes expose different sources of underperformance, such as advanced degradations rates, i.e., advance cell cracking, accelerated Potential Induced degradation (PID) rates, as well as lack of manufacturing quality issues. For the latter, stronger Light Induced Degradations (LID) rates, issues related to anti-reflective coating (ARC) and delamination are the main concerns.