Determination of the degradation modes and degradation rates of solar photo-voltaic (PV) modules in field exposure is of paramount importance in PV reliability studies. This contribution aims at the IV, IR, UV, and EL characterization of PV modules for determination of defects and correlation with the performance parameters (FF, Pmax, Isc) along with series resistance. 24 PV modules aged 18-19 years in hot desert conditions of Arizona, USA were subjected to various characterization techniques. First baseline light IV and dark IV was performed and the results were used to calculate the degradation in Pmax, Isc, FF, series resistances (Rs). The Pmax, FF, Isc, and Rs were degraded 1.36%/year, 0.53%/year, 0.88%/year, 3.026%/year respectively. After this IR, UV and EL imaging was performed on the modules. The IR thermography showed major temperature anomalies and hotspots causing overheating and reduced performance. The UV fluorescence imaging revealed encapsulant discoloration of moderate to severe levels that could cause a decline in the intensity of the radiation absorbed by the cells. The EL imaging showed substantial dark areas on all of modules.