A novel test method for quantifying cracking propensity of photovoltaic backsheets after ultraviolet exposure

Abstract

Surface cracking in multilayered backsheets is one of the common failure modes for field photovoltaic (PV) modules, leading to safety concerns. However, the current IEC qualification tests such as IEC 61215 cannot adequately predict the backsheet cracking in fielded modules. Moreover, little is known about effect of key environmental factors on the cracking behaviors of backsheets. In this study, a novel test method combining accelerated weathering with in situ surface cracking monitoring during tensile deformation is developed to quantify cracking propensity of backsheets after aging. A polyester‐based backsheet was selected, and 4 environmental conditions (UV/85°C/5% relative humidity (RH), UV/85°C/60% RH, 85°C/5% RH, 85°C/60% RH) were used for backsheet aging. The relationship between material degradation and crack formation of the backsheet under different environmental conditions is discussed. The channel cracks (fragmentation) perpendicular to the loading direction were only observed on the UV‐aged samples, not on those unaged or aged without UV irradiation. Moisture played a synergistic role with UV in the formation of surface cracking. Mode I fracture toughness (KIC) of the embrittled surface layer obtained from this test dropped by 98% relative to fresh samples, indicating a much higher cracking propensity of this backsheet after UV exposure. The proposed method was further validated by fragmentation tests of outdoor‐exposed backsheet samples. This method can serve as a quantitative tool to evaluate the cracking propensity of backsheets for a better material selection and lifetime prediction of PV modules.

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

“…Indoors tests or outdoors aging factors (e.g., ultraviolet (UV), temperature, relative humidity (RH) and their combinations) will set in motion a series of processes that leads to degradation. It has been reported that several PV degradation processes are associated with polymer degradation: Discoloration of encapsulants [1,2] and backsheets [3], backsheet cracking and chalking [4,5], and delamination [6][7][8]. It is therefore critical to understand which aging factor(s) influence the polymer degradation and to what extent.…”

Advanced analysis of backsheet failures from 26 power plants

“…This suggests that there might be a connection between chalking and the formation of backsheet cracks in polyamide layer structures. Furthermore, it has been demonstrated that, moisture inside the polymer plays a synergistic role with UV in the formation of backsheet cracking [10,11]. Backsheet chalking in AAA layer structures can therefore be evaluated as an early warning sign that indicates an elevated probability for the presence of a critical material and possible crack development in the future.…”

Effects of UV radiation on natural and synthetic materials

“…However, this surface degradation has not been shown to impact electrical output of the module. Upon UV degradation, (PET)/PET/EVA backsheets developed surface cracks (in the white TiO 2 filled PET outer/air-side layer) [ 182 ]. Cracking was absent in samples aged without UV irradiation.…”