Adhesion requirements for photovoltaic modules of polymeric encapsulation

Adhesion requirements for PV are often discussed but a detailed quantification based on scientific principles is outstanding. A test for the realistic assessment of requirements is presented. The difference between this test and the conventional peel test is that the test is conducted in-situ during ageing experiments in the climatic cabinet at realistic operating temperatures. Weights are attached to the backsheet of tested PV mini-modules to test stability of adhesion as devices being aged. This test is designed to identify the weakest interface of the multilayer encapsulation system and investigate the difference between field tests and failures (not) observed in certification testing. A series of samples was prepared under a wide range of lamination conditions. Different failure modes and ageing characteristics were observed. Some samples suffered quick failure of the adhesive bonds in the encapsulation system while others withstood forces of 20g/cm for 1000 hours. The test allows a clear discrimination between different samples and links closely to operational requirements.