The quality check of PV-plants under certain operating conditions by employing infrared-imaging has acquired significance during the last years. In order to prove the reliability of these techniques in terms of power loss, life time, critical temperatures and failure mechanisms, fifteen PV-plants were investigated in detail. In total, about 260 dismantled modules were analyzed by power measurements as well as electroluminescence and IR-thermography. Apart from revealing the reliability of this technique, the evaluated data manifest various failure mechanisms, like cell fracture, deficient solder joints, short-circuited cells and bypassed substrings. The impact of these frequently detected defects on the resulting temperature, the IV-curve and the power output is discussed. Finally, differing defects can be diagnosed by characteristic temperature differences. In conclusion, the reliability and usefulness of infrared-mapping of PV-plants were proved with the result, that all modules having cells with increased temperature show remarkably reduced power output. (C) 2012 Elsevier B.V. All rights reserved.