Backsheet degradation is a known reliability issue affecting field-exposed photovoltaic (PV) modules power plants. In this work, we present lessons learned during the last three years, examining modules from 26 power plants in the TestLab PV Modules at Fraunhofer ISE. The basis is a description of the currently observed backsheets and associated degradation features as for example backsheet chalking, cracks in different layers and chemical changes in composition. Furthermore, we lay out analytical methods for initial and more detailed analysis of the failures and module materials. For example, a method designated as “flashlight test” has been found to provide a quick and straightforward method to identify damaged polypropylene (PP) layers within backsheets. Furthermore, scanning acoustic microscopy (SAM) and a comparison of different variants of FTIR spectroscopy are presented.