Development of Testing Methods to Predict Cracking in Photovoltaic Backsheets

Kempe, Michael; Lockman, Trevor; Morse, Joshua

doi:10.1109/pvsc40753.2019.8980818

Cited by 13 publications

(17 citation statements)

References 11 publications

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“…The first is a coextruded three-layer PA-based BS ("PA1") that includes inner and outer layers comprising nylon-12 and TiO 2 (30 ± 2 μm thick) and a thicker core layer that comprises a nylon-12 and polypropylene (PP) blend with a glass fiber filler (285-μm thick). 18 The TiO 2 acts as a white pigment and partial UV blocker. PA1 is shown to have a wavy topography, where the thickness of each layer varies by on the order of 6 μm along its length.…”

Section: Materials and Test Samplesmentioning

confidence: 99%

“…Four commercial BS materials were examined in the study. The first is a coextruded three‐layer PA‐based BS (“PA1”) that includes inner and outer layers comprising nylon‐12 and TiO 2 (30 ± 2 μm thick) and a thicker core layer that comprises a nylon‐12 and polypropylene (PP) blend with a glass fiber filler (285‐μm thick) 18 . The TiO 2 acts as a white pigment and partial UV blocker.…”

Section: Bs Differentiation Studymentioning

confidence: 99%

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Advancing reliability assessments of photovoltaic modules and materials using combined‐accelerated stress testing

Owen‐Bellini

Hacke

Miller

et al. 2020

Progress in Photovoltaics

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Previously undiscovered failure modes in photovoltaic (PV) modules continue to emerge in field installations despite passing protocols for design qualification and quality assurance. Failure to detect these modes prior to widespread use could be attributed to the limitations of present‐day standard accelerated stress tests (ASTs), which are primarily designed to identify known degradation or failure modes at the time of development by applying simultaneous or sequential stress factors (usually two at most). Here, we introduce an accelerated testing method known as the combined‐accelerated stress test (C‐AST), which simultaneously combines multiple stress factors of the natural environment. Simultaneous combination of multiple stress factors allows for improved identification of failure modes with better ability to detect modes not known a priori. A demonstration experiment was conducted that reproduced the field‐observed cracking of polyamide‐ (PA‐) and polyvinylidene fluoride (PVDF)–based backsheet films, a failure mode that was not detected by current design qualification and quality assurance testing requirements. In this work, a two‐phase testing protocol was implemented. The first cycle (“Tropical”) is a predominantly high‐humidity and high‐temperature test designed to replicate harsh tropical climates. The second cycle (“Multi‐season”) was designed to replicate drier and more temperate conditions found in continental or desert climates. Testing was conducted on 2 × 2‐cell crystalline‐silicon cell miniature modules constructed with both ultraviolet (UV)–transmitting and UV‐blocking encapsulants. Cracking failures were observed within a cumulative 120 days of the Tropical condition for one of the PA‐based backsheets and after 84 days of Tropical cycle followed by 42 days of the Multi‐season cycle for the PVDF‐based backsheet, which are both consistent with failures seen in fielded modules. In addition to backsheet cracking, degradation modes were observed including solder/interconnect fatigue, various light‐induced degradation modes, backsheet delamination, discoloration, corrosion, and cell cracking. The ability to simultaneously apply multiple stress factors may allow many of the test sequences within the standardized design qualification procedure to be performed using a single test setup.

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Section: Materials and Test Samplesmentioning

confidence: 99%

Section: Bs Differentiation Studymentioning

confidence: 99%

Advancing reliability assessments of photovoltaic modules and materials using combined‐accelerated stress testing

Owen‐Bellini

Hacke

Miller

et al. 2020

Progress in Photovoltaics

Self Cite

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show abstract

“…The material was found to have a suitable RTI rating for tensile strength, likely due to the fiberglass content. After as little as 4 years of field exposure, 28–36 deep cracks formed all the way through the backsheet creating ground faults and consequent safety concerns. Post hoc testing revealed that thermal and/or UV aging caused a precipitous drop in elongation to break (that was not evaluated) but did not cause the tensile strength to decrease 35,36 …”

Section: Rti/rte/ti Testingmentioning

confidence: 99%

Standards development for modules in high temperature micro‐environments

Kempe

Holsapple

Whitfield³

et al. 2021

Progress in Photovoltaics

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Photovoltaic (PV) module qualification standards, IEC 61215 and IEC 61730, were designed to apply to “general open‐air climates” and IEC 61730 specifically indicated applicability of ambient air temperature of 40°C. Additionally, these standards provided allowances for so‐called “open rack mounted PV modules” without a clear definition of “open‐rack.” These implied restrictions and allowances meant that hotter climates or thermally restrictive installation methods may not be covered by these often customer‐mandated certification standards. This is particularly salient for the significant growth regions of the Middle East and India that would be expected to operate at significantly higher temperatures. The applicability of these documents raised issues over the definition of “open rack” and the fact that the geographic location is just as important as the mounting configuration in assessing the impact of the micro‐environment of a PV module. This work summarizes the scientific background for IEC Technical Specification 63126:2020 ED1, titled “Guidelines for qualifying PV modules components and materials for operation at high temperatures.” This standard was recently published by the IEC and is the first step in a systematic effort to rework these standards to address the question of temperature more directly. Instead of specifying a mounting condition, we specify different suites of tests suitable for a system (PV module, mounting style, and location) defined by the 98th percentile cell temperature. With a defined temperature regime to work from, this allowed us to use existing literature research combined with additional modeling work to determine, which tests would need to be modified. This resulted in suggested changes to material thermal indices, thermal cycling temperatures, hot spot testing, ultraviolet testing, and bypass diode testing among other tests and characteristics described herein.

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“…[7][8][9][10][11] Single stress tests are generally performed under various combinations of exposure to damp heat (DH), ultraviolet (UV), and thermal cycling (TC). Sequential tests 12,13 are recommended by some 3rd parties, such as researchers at the National Renewable Energy Laboratory (NREL) [14][15][16] and Photovoltaic Evolution Labs (PVEL), 17,18 which can better simulate field conditions and observed failure modes. A comprehensive aging test, combining UV, DH, and TC together, 19 was also developed at DuPont.…”

Section: Introductionmentioning

confidence: 99%

Impact of specimen preparation method on photovoltaic backsheet degradation during accelerated aging test

Xia

Liu²,

et al. 2022

Energy Science & Engineering

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In this study, we highlight some important factors in the specimen preparation methods for evaluating photovoltaic backsheet properties after accelerated aging. Two different sequences are considered: Method (I) cut-then-age: cut into 1-cm wide strips and then expose to stress, and Method (II) age-then-cut: expose a larger sheet to stress and then cut into 1-cm widths for mechanical property measurements. We also compare the effect of three cutting methods, (a) tensile specimen punch, (b) paper cutter, and (c) fresh razor blade. Several commercial backsheets were evaluated, with stress exposures including (a) pressure cooker test (PCT), (b) dry ultraviolet (UV) radiation exposure, and (c) UV combined damp heat tests. Fourier transform infrared spectrometer (FTIR) and intrinsic viscosity (IV) were used to analyze the materials on unstressed materials and samples exposed to PCT. The results show that both the cutting method and the time of cutting have an impact on the backsheet mechanical properties. Under UV exposure, Method II, age-then-cut, generally resulted in a higher average value, with more variation than Method I; however, if the side strips from Method II were excluded, the variation dropped to the same level. This is because the specimens at the sides of the sheet get additional damage from UV light from the exposed sides of the sample. In contrast to UV exposure, PCT specimens prepared by Method II result in lower average values and higher variability. This is attributed to embrittlement through the bulk of the sample where the cutting of embrittled specimens appears to result in more edge defects which can then initiate a break at smaller strains. The data suggest that for UV exposures, the specimens should be cut after aging and the exposed side specimens discarded, and that for PCT exposures, the specimens should be cut before the exposure.

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Development of Testing Methods to Predict Cracking in Photovoltaic Backsheets

Cited by 13 publications

References 11 publications

Advancing reliability assessments of photovoltaic modules and materials using combined‐accelerated stress testing

Advancing reliability assessments of photovoltaic modules and materials using combined‐accelerated stress testing

Standards development for modules in high temperature micro‐environments

Impact of specimen preparation method on photovoltaic backsheet degradation during accelerated aging test

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