Effect of Backsheet Properties on PV Encapsulant Degradation during Combined Accelerated Aging Tests

Abstract

Long-term photovoltaic (PV) module reliability is highly determined by the durability of the polymeric components (backsheet and encapsulation materials). This paper presents the result of experiments on encapsulant degradation influenced by the backsheet permeation properties. Towards this goal, one type of ethylene/vinyl acetate copolymer (EVA) was aged in glass/EVA/backsheet laminates in accelerated aging tests (up to 4000 h for Damp-Heat (DH) and up to 480 kWh/m2 for UV and UV-DH combined). The samples contained three backsheets with different permeation properties to examine their impact on EVA degradation. Thermal and chemical characterization shows that the EVA degradation is stronger with the glass–EVA–polyamide (PA)-based backsheet than with the polyethylene terephthalate (PET)-based backsheets. The higher oxygen transmission rate (OTR) of the PA-based backsheet may increase photo-oxidation and aggravating the degradation of EVA in the laminates. Furthermore, FTIR results were used to demonstrate the effect of damp heat exposure on the EVA interfaces, showing an accelerated degradation at the glass–EVA interface. The comparison of accelerated aging stress factors reveals that EVA suffers the strongest chemical and optical degradation when high UV, high temperature and high relative humidity are combined simultaneously.

Environmental Durability of an Optical Fiber Cable Intended for Distributed Strain Measurements in Concrete Structures

“…-An enthalpic jump is visible around −30 °C, which can be attributed to the glass transition of the amorphous phase of the EVA copolymer; -A large endothermic region is observed between −30 and 110 °C, from which three distinct peaks emerge at approximately 40, 50 and 90 °C. This domain corresponds to the melting temperature range generally reported for the crystalline phase of EVAs [42,43,46]. The presence of multiple peaks reveals the existence of several populations and sizes of crystalline lamellae.…”

“…Vinyl acetate groups, which are esters, are known to be very sensitive to various environmental factors such as temperature, ultraviolet (UV) radiation, or oxygen. They can easily decompose to generate free radicals, which can then form different carboxylic acids [ 42 , 43 ]. In the present case, FTIR analyses confirm that the thermal degradation of ester groups occurred for samples immersed in the alkaline solution at 40 and 60 °C.…”

Statistical analysis of 12 years of standardized accelerated aging in photovoltaic‐module certification tests

“…Wet leakage fail rates are below 4% for all test sequences, and out of these highest for DH1000 and Sequences B and B1. This is most likely due to degradation of encapsulant 19 or backsheet. 20 The dry insulation rates are very low (<1%) and were only ever recorded for DH1000 and TC200 over the complete time frame.…”

Advanced analysis of backsheet failures from 26 power plants

“…Furthermore, a degraded backsheet can initiate secondary moisturedependent degradation processes inside the module, e.g., corrosion, which additionally impair module performance in the long term [4]. An improved understanding of backsheet degradation mechanisms [5] is essential to determine cost-effective detection and mitigation procedures [3]. This knowledge can be utilized to develop alternative materials to avoid similar issues in the future.…”