Standardizable Test Procedure for PV Module Backsheets

How can current solar modules be further improved? Until now, the service life of a photovoltaic module has been estimated at 25 years. However, recent field studies have already revealed obvious changes in material properties after just a few years (4-8), such as cracks in the backsheets of PV modules or delamination of individual layers of the backsheets. Since these backsheets protect the solar cell from environmental influences such as moisture and other pollutants and serve to provide electrical insulation and mechanical stability, such defects are associated with safety risks and yield losses.

Back sheets are made from various materials such as polyamides, polypropylene, polyvinylidene fluoride, or polyethylene terephthalate and are exposed to a combination of stress factors. They must withstand temperature cycles, moisture, light (especially the UV component of sunlight), and other influences such as salt, dust, or high electrical system voltages. The current testing standards do not adequately cover these environmental stresses.

In the joint project “PolymAERA,” a consortium of research institutes, including Fraunhofer CSP in Halle (Saale), is working to gain a better understanding of the operating conditions, their interactions with the module, and the physical-chemical degradation processes. The aim of the project is to develop a standardizable and internationally accepted test that makes it possible to check the suitability of backsheets and modules, including processing, for a service life of more than 20 years under real operating conditions in the field. The tests developed and the evaluation of fault patterns will then be validated in a ring test between the partners and possibly other external partners, which should also provide information on reproducibility and variation between laboratories. Finally, the findings will be presented to national and international committees for the improvement of existing standards.

"Our primary goal at Fraunhofer CSP is to create a test matrix for analyzing the influence of test conditions and material changes. In addition to the classic environmental conditions of humidity, temperature, and UV light, we want to investigate the influence of increasing system voltages, 1,500 volts and possibly higher, on the backsheets. Against the backdrop of the growing market share of bifacial PV modules, we are also paying special attention to the optical properties and dielectric strength as a function of aging, as well as the influence of the backsheet on, for example, potential-induced degradation (PID) when using bifacial cells," says Dr.-Ing. Bengt Jäckel, group manager for “PV Modules, Components, and Manufacturing” at Fraunhofer CSP.

See also: Research project Anomalous