Modelling of conditions for accelerated lifetime testing of Humidity impact on PV-modules based on monitoring of climatic data

Water is considered as an important degradation factor for PV-modules by causing hydrolysis of polymeric components, corrosion of glass and of metallic components like grids and interconnectors. The type approval testing of PV-modules according to the IEC standards takes water into account by means of the so called Damp-Heat test and the Frost-Thaw test. The test-conditions were designed long time ago and initially meant to reflect the service life of a module, but the type approval testing is not applicable for prediction of long-term durability behaviour, but a qualification test for the assurance of a minimum quality level.Basically absorption and mass transport of water into and within the module has to be considered. These phenomena depend on the ambient climate of the PV-module in use, the design (back-sheet, glass-glass, all polymer, e.g.), the operation conditions (rack-mounted, on rooftop, building integrated) and the material composition. We try to evaluate test conditions that are primarily based on the stresses occurring during the operation at specific locations by using monitored climatic data and applying phenomenological models for the estimation of the moisture load at the surfaces of PV-modules as function of the module temperature. A simple time transformation function was used for the design of appropriate damp-heat tests as accelerated service life tests. The evaluated testing times differ up to an order of magnitude for different climatic locations, depending on the kinetics of the dominant degradation processes.

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► A phenomenological model for the evaluation of the effective surface humidity of PV-modules is proposed, which allows the estimation of the moisture load at the surfaces of PV-modules as function of the module temperature.
► A simple time transformation function was used for the design of appropriate damp-heat tests as accelerated service life tests.
► The evaluated testing times differ up to an order of magnitude for different climatic locations, depending on the kinetics of the dominant degradation processes and show the option of the definition of different stress categories and the design of adapted PV-modules.