Correlation of the loss in photovoltaic module performance with the ageing behaviour of the backsheets used

Self Cite

As the PV market shows enormous potential with huge growth rates especially in climatic‐sensible regions, specific artificial ageing test procedures are a key point for an efficient and fast product development of new PV modules/materials optimized for the use in specific climatic regions. Based on the definition of four climate profiles (dry and hot—arid, moderate, humid, and hot—tropical and high irradiation—alpine), a program was worked out with 14 climate specific test conditions for accelerated ageing tests. The big challenge in this respect was the adaption/advancement of existing standard procedures for PV modules/components testing in a way that reliable testing for certain climatic conditions optimized PV modules is possible. The time‐dependent repeated application of combined climatic and environmental stresses (temperature, temperature cycles, humidity, irradiation, mechanical load, salt mist) was used to induce performance losses, material degradation, and failures in test modules which resemble those effects occurring in real‐life PV installations under comparable climatic and environmental conditions. For this demanding task, a large number of identical test modules with respect to composition and module design was manufactured. A detailed nondestructive analysis/characterization of all modules was performed: (1) before; (2) during (six intermediate stages); and (3) after the accelerated ageing test. The nondestructive characterization methods used to follow the module's ageing processes throughout the whole accelerated ageing procedure were current‐voltage characteristics measurements and electroluminiscence images for the electrical performance evaluation and ultraviolet fluorescence (spectroscopic and imaging) measurements, Fourier transform infrared spectroscopy as well as colour measurements of the backsheets outer layer for recording of chemical changes of the encapsulant and backsheet. The electrical and material characterization data were incorporated in an optimized database. As stated above, a set of three identical modules was exposed together in the respective climate specific ageing tests and subsequently characterized in order to increase statistical reliability of the measuring results. The analysis of the data and first approaches of advanced data treatment have already clearly shown that the electrical and material degradation of the test modules is dependent on (1) the type and combination, (2) duration, and (3) mode (sequential versus constant) of the stresses applied. On the one hand, the simulation of environmental stresses like heavy snow and wind load and enhanced frequency of temperature cycling resulting in cell cracks and cell connector breakage could be demonstrated. Additional treatment in salty atmosphere, on the other hand, did not show an accelerating effect on degradation on the electrical or material side. The accelerating effect of enhanced temperature, humidity, or additional irradiation on the degradation of power and materials could be shown very well. D...

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Climate specific accelerated ageing tests and evaluation of ageing induced electrical, physical, and chemical changes

Eder

Voronko

Dimitriadis³

et al. 2018

Self Cite

“…The backsheet is the first line of protection of the backside of photovoltaic (PV) modules against environmental elements. Degradation of the backsheet including blistering and cracking (Figure A) is commonly observed in field and after accelerated testing and can compromise module reliability . Mechanical characterization of backsheets has mostly involved delamination and tensile testing; however, there remains a significant lack of understanding in the cracking or tearing properties in spite of their importance to the reliability of PV modules.…”

Section: Introductionmentioning

confidence: 99%

Tearing and reliability of photovoltaic module backsheets

Yuen

Moffitt

Novoa³

et al. 2019

The backsheet in photovoltaic modules belongs to an important class of layered materials where the tearing behavior of the individual layers does not necessarily represent the tearing behavior of the entire backsheet. Such characteristic arises from the interaction between the individual layers during the tearing process, where one layer of the backsheet is mechanically constrained by its neighboring layers and the layers may debond from each other. The mechanical constraint and debonding change the amount of energy dissipated during tearing and affect the overall tearing energy. In this work, we exposed a wide selection of backsheets with polymers including ethylene‐vinyl acetate (EVA), polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), and ethylene tetrafluoroethylene (ETFE) to damp heat (85°C/85%RH) for up to 2000 hours. We report on the effect of damp heat on the tearing energy as a function of damp heat exposure. We developed a model that describes the tearing energy of a layered structure by accounting for the tearing of the individual layers in the backsheet, the effect of mechanical constraint, and the adhesive debonding between the layers. Additionally, we explore the relationship between the microstructural change in the polymers which resulted from the damp heat exposure and the mechanical properties using modulated differential scanning calorimetry (MDSC), small and wide angle X‐ray scattering (SAXS and WAXS), and tensile testing.

“…Extensive efforts have been made to characterize the backsheet degradation based on changes in yellowing, chemical structure and microstructure, tensile strength, adhesion strength, and other bulk thermo or mechanical properties . However, limited studies have investigated backsheet cracking, probably because it is challenging to reproduce the cracking observed in the field using accelerated aging tests.…”

Section: Introductionmentioning

confidence: 99%

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

Lin

Jacobs

et al. 2018

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.