Ethylene Vinyl Acetate Degradation Research Articles

Effect of EVA discoloration in 25-year-old single crystalline silicon photovoltaic modules operated under moderate climate

In this study, the effect or absence thereof of discoloured ethylene vinyl acetate (EVA) on the electrical characteristics of photovoltaic (PV) modules was investigated. The field samples for discoloured EVA were PV modules that had been in operation for 25 years since 1986 in a modulated climate in South Korea. The I-V characteristics of 25-year-old, discoloured single crystalline silicon (sc-Si) PV modules were measured, and the results showed that the maximum power (Pmp) had degraded by approximately 25.5 %. The sc-Si single-cell PV module had a discoloured EVA, which was separated from it to determine the correlation between the discoloration of EVA and power degradation. The yellowness index (YI) of the EVA was in the range of 36–44. The relationship between the YI and transmission of 25-year-old discoloured EVA was also determined through measurements. The short-circuit current (Isc) and Pmp of the PV modules were measured, which were found to be degraded by 22.2 % and 21.3 %, respectively, owing to the discoloured EVA. The output characteristics of the solar cell in the discoloured region of the EVA were analysed. The results showed that the Isc degradation rate varied linearly with the EVA discoloration area. The discoloration of the EVA was the main effect (83.5 %) among the failure modes of the 25-year-old sc-Si PV module. It accounted for 0.85 % of the 1.02 % annual degradation of the PV module. Isc and Pmp exhibited linear degradation corresponding to areas of 25 %, 50 %, 75 %, and 100 % discoloration in single-cell PV modules.

Photoluminescence for Defect Detection on Full-Sized Photovoltaic Modules

Cost-effective, fast, and nondestructive on-site characterization of photovoltaic plants is required to determine countermeasures against power loss, defects, or safety problems. Methods with small impact on the operation and a high throughput, such as infrared thermography (IR), or methods with high resolution for detailed defect information, such as electroluminescence (EL) imaging, are expedient. To combine high resolution and high throughput, we propose to use photoluminescence (PL) as an outdoor characterization method for full-sized module imaging. With PL imaging as with IR imaging, no electrical contact is necessary, yet image resolution is on par with EL images. Our outdoor PL setup features an excitation source with 18 broadband, white, high power, chip on board LEDs coupled with low-cost short pass filters. This setup is suitable for indium gallium arsenide and silicon detectors. Here, we compare the visibility of common defects, including short-circuited bypass diodes, cracks, potential induced degradation, snail trails, ethylene-vinyl acetate degradation, and interconnection failures, in PL images to that in state-of-the-art imaging techniques IR, EL, and ultraviolet fluorescence. We find that out of these seven defects, five can be detected well, cell cracks under certain conditions, and interconnection failures not at all. We discuss how different techniques are complementary to enable better defect detection.

Predicting Early EVA Degradation in Photovoltaic Modules From Short Circuit Current Measurements

One of the common failures in photovoltaic modules is the degradation of the ethylene-vinyl acetate (EVA) encapsulant due to prolonged ultraviolet exposure and other environmental stress factors, such as temperature and humidity. Experimental studies have shown that significant reduction in the optical transmission due to EVA degradation leads to loss in the available power by more than 50%. In this article, a novel approach to predict the early degradation of EVA encapsulant is proposed by correlating EVA degradation with short-circuit current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ). An electrical circuit simulator, simulation program with integrated circuit emphasis (SPICE), is used to evaluate the short-circuit current obtained under varying optical transmission caused by EVA discoloration. The simulation follows three steps: simulation of the transmitted solar spectrum; simulation of the spectral short-circuit current density; and simulation of the current-voltage (I-V) curve to obtain short-circuit current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ), maximum power output (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ), open-circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> ) and fill factor. Results show that the reduction in short-circuit current due to EVA degradation differs from the reductions expected due to a spectrally-uniform reduction of intensity of the solar irradiance. Both types of variation are linear, however, the slope due to EVA degradation is larger than the slope obtained for normal intensity variations in the solar irradiance. This model, when applied in conjunction with solar irradiance measurements, can predict early onset of EVA encapsulant failure, thereby enabling preventative measures to be taken.

Structural composition and thermal stability of extracted EVA from silicon solar modules waste

Ethylene-vinyl acetate (EVA), a copolymer of ethylene and vinyl acetate, is widely used as an encapsulant in the silicon solar module to bind the different layers together and protecting the solar cells from over stressing, cracking, and environmental effects. In this work, EVA has been recovered successfully from the used silicon solar module by thermal treatment at 170 °C temperature and the application of mechanical force. The established process is completely environment-friendly, as the EVA layer was recovered without any degradation and emission of any gas. The presence of extracted EVA and its chemical composition was confirmed from FTIR and EDAX measurements. It was observed from Thermogravimetry (TGA) and Differential thermogravimetry (DTG) that thermal degradation of EVA was a two-step process, and also the rate of reaction was fast in an air environment as compared to nitrogen environment. The extracted EVA is thermally stable until 215 °C in the air environment. From Differential scanning calorimetry (DSC) analysis, two endothermic peaks were observed at temperature 37 °C and 55 °C, which may be due to beginning of melting of vinyl acetate and ethylene crystallites respectively in air and nitrogen environment. From UV–visible spectroscopy, it was found that above 500 nm, the extracted EVA is transparent. After examined through the various characterization, it has been observed that extracted EVA shows quite similar properties as that of commercially available EVA. Therefore, the recovered EVA may be used in the encapsulation of solar modules and other applications in packaging and textile industries.

Field-Aged Glass/Backsheet and Glass/Glass PV Modules: Encapsulant Degradation Comparison

Ethylene vinyl acetate (EVA) is the predominant encapsulant in crystalline-silicon photovoltaic (PV) modules; however, its degradation is a subject of major concern, which causes significant power loss under field conditions. This article presents a comparison of EVA degradation in field-aged PV modules with glass/backsheet (G/B) and glass/glass (G/G) architectures. Modulelevel characterization included UV fluorescence imaging and I-V measurements. Material analytical techniques, including colorimetry, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy, were performed to correlate the module performance parameters with EVA material properties. An intense EVA discoloration in G/G modules was observed, which was corroborated by higher module Isc and Pmax degradation rates compared with its counterpart G/B modules. Higher power degradation was accompanied by a significant increase in EVA crosslinking, vinyl acetate content, yellowness index, and presence of functional groups containing unsaturated moieties that are linked to degradation products of photothermal reaction, and a higher decrease in the degree of crystallinity. The absence of a polymeric backsheet in hermetically sealed G/G modules, which restricts photobleaching and enhances the entrapment of volatile acetic acid and other degradation by-products, plays a major role in causing higher EVA degradation in G/G modules. This article concludes that EVA might have been a good choice of an encapsulant for the G/B modules over the decades, but it may prove to be an inappropriate choice for the G/G modules because of potential degassing, corrosion, and/or discoloration issues. Ionomers or polyester-based encapsulants like polyolefins could be best suited for G/G modules as it appears to be a current trend in the industry.

Fabrication of hydrotalcite containing N/P/S and its ternary synergistic efficiency on thermostability and fire resistance of ethylene vinyl acetate (EVA)

Nitrate intercalated hydrotalcite (NO3−‐HTC) was first prepared as precursor; a schiff base derivative containing N, P, and S was synthesized and its structure was characterized. Later the schiff base derivative was used as intercalation to replace NO3− in hydrotalcite. The final product was schiff base derivative intercalated hydrotalcite, which was named as benzaldehyde–taurine–hypophosphorous (BTP)‐HTC. The results showed both NO3−‐HTC and BTP‐HTC can effectively improve the flame retardant and thermostability of ethylene vinyl acetate (EVA). In cone calorimeter test, the peak heat release rate of EVA was 1421.2 kW/m2 and reduced sharply to 746.1/584.5 kW/m2 for 20 wt% NO3−‐HTC/BTP‐HTC adding, respectively. At same time, the total heat release was also decreased from 120.6 MJ/m2 for EVA to 81.0/70.0 MJ/m2, respectively. Morphology observation and composition analysis by scanning electron microscopy (SEM)/X‐ray spectroscopy (EDS) documented the residue left after combustion of EVA/NO3−‐HTC was just ash containing Mg and Al; but for EVA/BTP‐HTC, coherent char layer containing Mg, Al, and P was left. Thermogravimetric analysis indicated that the thermal degradation of EVA was prolonged by either NO3−‐HTC or BTP‐HTC; and char content was kept to 8.6% and 11.0%, respectively. The whole results documented either NO3−‐HTC or BTP‐HTC improved the combustion behavior and thermostability of EVA, and BTP‐HTC showed excellent effect. J. VINYL ADDIT. TECHNOL., 25:255–261, 2019. © 2018 Society of Plastics Engineers

Review on degradation of EVA encapsulated PV Module by UV ageing

Solar energy is considered to be one of the prime sources of renewable energy for the generation of electrical energy, which is gaining the importance in recent time in India and there is a plan to generate 200GW of solar energy by 2024. Solar energy is absorbed by Photo-Voltaic (PV) cells and converted into electrical energy. Such PV cells are connected in series and parallel combination to generate required output power. Hence, Photo-Voltaic (PV) modules must be in operation for long time without any reduction in output and efficiency. In recent times, to achieve this, both surfaces of PV module are encapsulated by Ethylene-Vinyl-Acetate (EVA) polymer, but UV radiations leads to degradation of EVA polymer, which results in deterioration of PV module, thus overall efficiency and output of module reduces. Various UV accelerated ageing studies and investigations have predicted service time of module. The objective of this investigation is to review the available literature with respect to types of PV cells & encapsulant used, UV ageing parameters & instruments employed and envision a way forward in employing EVA with nano additives as an encapsulant to improve its performance.

The thermo-mechanical degradation of ethylene vinyl acetate used as a solar panel adhesive and encapsulant

The thermal ageing of an ethylene-vinyl acetate (EVA) polymer used as an adhesive and encapsulant in a photovoltaic module has been investigated. The EVA is used to bond the silicon solar cells to the front glass and backing sheet and to protect the photovoltaic materials from the environment and mechanical damage. Using a range of experimental techniques, including Dynamic Mechanical Analysis, Differential Scanning Calorimetry and Thermo-gravimetric Analysis, it was possible to show a link between changes in mechanical properties with both the transient temperature and the degree of long-time thermal ageing. Importantly, it was possible to show that the ageing related property changes were likely due to long term structural changes rather than any modification of the chemistry of the material.

Degradation behaviors of EVA encapsulant and AZO films in Cu(In,Ga)Se2 photovoltaic modules under accelerated damp heat exposure

This paper focuses on the degradation behavior of ethylene vinyl acetate (EVA) and Al-doped ZnO (AZO) films in CIGS PV modules after the damp heat test. We observed losses of the FF and efficiency in the modules after 1000h of damp heat (DH) exposure and some of them were discolored from the outside edge and the center. To clarify the degradation behavior of the non-discolored and discolored modules, a failure analysis for each position of the EVA and AZO in the CIGS module films from the edge to the center was performed. The resistivity of the AZO films in the non-discolored modules increased due to the adsorption of oxygen. In discolored modules, the resistivity of the AZO films rapidly increased at the edge region, and the morphologies of the AZO films were also changed due to the chemical degradation of EVA. These degradation behaviors of the AZO films and EVA in discolored modules were attributed to the formation of hydroxyl and carboxylic species caused by water penetration. Moreover, we reported that the transmittance and the mechanical properties of EVA after 1000h DH exposure were deteriorated by water molecules.

Flame retardancy and thermal degradation of intumescent flame retardant EVA composite with efficient charring agent

Intumescent flame retardant ethylene-vinyl acetate (EVA) composites with ammonium polyphosphate (APP) and efficient charring agent (CNCA-DA) were prepared through melt blending. The effect of APP and CNCA-DA on the flame retardant properties and thermal degradation of EVA were investigated by the means of limited oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA), cone calorimeter test (CCT), scanning electron microscopy (SEM), laser Raman spectroscopy (LRS), and Fourier transform infrared (FTIR). The results from LOI and UL-94 showed that the intumescent flame retardant (IFR) containing CNCA-DA and APP was very effective in flame retardancy of EVA. When the mass ratio of APP and CNCA-DA was 3:1, the IFR showed the best effect, and when the IFR loading held 30%, the LOI value reached 32.1%. It was also found that when the IFR loading held only 20%, the flame retardancy of EVAP/IFR can still pass V-0 rating in UL-94 tests, meanwhile, its LOI value reached 27.0%. As for CCT results, IFR could clearly change the decomposition behavior of EVA and formed an intumescent char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and mass loss (ML). In addition, the morphological structures which were observed by digital photos and SEM manifested that IFR could promote to form the continuous and compact intumescent char layer. The analysis of LRS and FTIR indicated that EVA/IFR could form POP and POC connected structures as well as polyaromatic structure. When APP and CNCA-DA were combined together, the suitable strength of char layer was obtained to improve the flame retardant properties.

Mechanical Ageing Protocol Selection Affects Macroscopic Performance and Molecular Level Properties of Ethylene Vinyl Acetate (EVA) Running Shoe Midsole Foam

Existing attempts to evaluate footwear via cyclic compression fail to sufficiently represent biofidelic force-time curves or provide the underlying mechanism of EVA foam fatigue. A uniaxial biofidelic waveform was compared to a sine wave of the same frequency to examine differences in (1) net displacement, (2) absorbed energy, and (3) peak force from ASTM F1614. A non-destructive molecular-level technique (ATR-FTIR) recorded differences in hydroxyl, ester, and unsaturated moieties due to EVA degradation. It was concluded that (1) biofidelic waveforms may better simulate human running, (2) material degradation is discernible, and (3) inferences regarding polymeric degradation and macroscopic performance require further investigation.

Thermal endurance study of polymers used in low concentration photovoltaic modules

Thermal endurance studies were performed on the major polymeric components used in a Low concentration photovoltaic (LCPV) module using a thermal gravimetric analysis (TGA) method. Activation energy of the various polymers was obtained, and lifetimes were predicted based on the assumption of 5% weight loss for 30 years. Oven aging was used to verify the TGA thermal endurance prediction. Reasonable agreement between TGA prediction and oven baking results were reached, with the exception of ethylene-vinyl acetate (EVA) encapsulant that demonstrated a second-order reaction inconsistent with TGA assumptions. As a result, a more LCPV-relevant way to characterize the degradation of EVA was developed and demonstrated a linear relationship between PV device short-circuit current degradation and yellowness index. For the purpose of this EVA degradation analysis, a 20% reduction in PV device short circuit current was selected as the failure criteria.

Qualitative study of the evolution of the composition of the gas evolved in the thermal and HY-catalytic oxidative degradation of EVA copolymers

In this work, a study of the evolution with the temperature of the qualitative composition of the gas evolved in the degradation of ethylene-vinyl acetate (EVA) copolymers under air atmosphere has been carried out using on-line analysis by thermogravimetry (TGA) combined with FTIR spectrometry (TGA/FTIR). Three commercial EVA copolymers were selected, and the results obtained in the experiments performed in the presence and in the absence of HY zeolite are compared. The air atmosphere causes significant differences among the thermal and catalytic pyrolysis. The oxidative pyrolysis involves four main decomposition steps, and each of them also involves different types of reactions. In the first stage, the loss of acetoxi groups of the VA units occurs, with formation of acetic acid, but also CO, CO 2 and carbonylic compounds are produced, increasing the formation of these compounds as the VA content of the copolymer decreases. The second and third decomposition steps, which are better distinguished as the VA content of the copolymer increases, correspond to the degradation of the polymeric chain which results from the previous step, and involves cracking reactions, without O 2 consumption, as well as oxidation reactions. Finally, the fourth reaction step corresponds to the slower oxidation of the carbonous residues formed in the previous stages. The presence of the HY zeolite contributes to a decrease of the CO and CO 2 formation, or in other words, to an increase of the reactions without oxygen consumption.

Degradation and stabilisation of poly(ethylene- stat-vinyl acetate): 1 – Spectroscopic and rheological examination of thermal and thermo-oxidative degradation mechanisms

The degradation of ethylene vinyl acetate (EVA) copolymers was compared with low density polyethylene (LDPE), poly(vinyl acetate) (PVAc) and poly(vinyl chloride) (PVC) using FTIR, UV–visible and fluorescence spectroscopy as well as thermal and rheological analyses. Thermal, thermo-oxidative and photo-oxidative studies were conducted. Thermo-oxidation below 180 °C shows more similarities between EVA and LDPE. The luminescence spectra of degraded EVA and LDPE were almost identical but very different to that of PVAc. UV–vis analysis showed that the polyenes present in aged PVC were unlikely to be the same species responsible for the observed colour formation in aged EVA. It is suggested that they are polyconjugated carbonyl products. Rheological analysis also showed the evolution of crosslinking reactions during thermo-oxidation. FTIR studies after thermal degradation in inert conditions 290 °C showed complete loss of the ester functionality and associated lactone formation along with some evidence for ketonic and unsaturated carbonyl groups. Degradation in air at 180 °C, however, revealed that loss of the ester group was not so marked, with PVAc exhibiting the greatest stability. This was in line with the induction time to onset of autocatalytic carbonyl growth at 180 °C; the latter showed an apparent exponential decrease with increasing vinyl acetate content up to 28% w/w. Fluorescence analysis produced trends that complemented those of carbonyl index; the time to decomposition of initial fluorescent α,β-unsaturated carbonyl species coincided with the time to onset of carbonyl growth. Furthermore, the rate of formation of the new fluorescent species produced in EVA, and LDPE was similar to that of carbonyl growth. These new fluorescent species are therefore likely to be di- or tri-carbonyl products.

EVA encapsulants for pv modules: Reliability issues and current R&D status at NREL

We briefly summarize ethylene-vinyl acetate ( EVA) reliability issues and report our R&D results. These results include EVA degradation effects, discoloration factors, approaches to mitigate the EVA discoloration, improved photostability of modified EVA formulations, and plans to identify the best encapsulation schemes and to develop appropriate methodologies for predicting service life of PV modules.

Thermal degradation of EVA and EBA—A comparison. I. Volatile decomposition products

AbstractThis is the first in a series of papers in which structural changes during thermal degradation of ethylene‐vinyl acetate (EVA) and ethylene‐butyl acrylate (EBA) copolymers are compared. EVA, containing 11.4 mol% vinyl acetate (VA) and EBA, containing 5.4 mol% butyl acrylate (BA), were pyrolyzed at 280°C in nitrogen for 30 min. In another series of pyrolysis, EVA containing 1.2, 2.2, and 11.4 mol% VA were treated at 150–190°C for 3 h. The volatile decomposition products were collected in cooled traps respectively gas bags and then analysed with GC‐MS and ion‐chromatography. EVA is rather labile. The main volatile decomposition product is acetic acid. A linear decomposition rate was found already at the lowest investigated pyrolysis temperature, 150°C. After 30 min at 280°C every 15th of the acetate side groups had been eliminated. EBA is much more stable to pyrolysis. Thirty minutes at 280°C resulted in a decomposition of one out of 1500 BA groups. Butene is the main volatile decomposition product. Ester pyrolysis is supposed to account for the degradation of both types of polymers. The big difference in reactivity is presumably due to conformational differences. The ester pyrolysis mechanism will result in random unsaturations in EVA and carboxylic groups in EBA. To a minor extent acetaldehyde is formed when EVA is degraded. According to the mechanisms suggested, carbonyl groups remain in the main chain. Contrary to what is reported for poly(butyl acrylate), no alcohol was formed when pyrolysing EBA. This indicates that adjacent acrylate groups are needed for alcohol formation. For both types of polymer, scissions of the main chain results in hydrocarbon fragments mainly. In addition, acrylate containing fragments are observed when EBA is degraded. EVA, however, does not give any acetate‐containing fragments.

Thermal degradation of EVA and EBA—A comparison. II. Changes in unsaturation and side group structure

AbstractThis is the second in a series of papers in which the thermal degradation of ethylene‐vinyl acetate (EVA) and ethylene‐butyl acrylate (EBA) copolymers are compared. The EBA samples contain 0.8, 1.6, and 5.4 mol % butyl acrylate (BA), respectively, and the EVA samples 1.2 and 6.7 mol % vinyl acetate (VA). The samples were heated in nitrogen in a tubular oven at 285, 333, 350, 370 and 390°C for 6–120 min. The samples were analyzed with IR, NMR, gravimetry, and titration of carboxylic groups. The EVA samples were rapidly degraded by deacetylation, which was complete after about 30 min at 333°C. A linear relation between the loss of acetate groups and the formation of trans double bonds was found. A small amount of keto groups and traces of lactones were also observed. The data confirm the previously proposed mechanisms for deacetylation and the formation of acetaldehyde. A mechanism for lactone formation is suggested. The deacetylation rate is increasing with the VA content, presumably because of an increased amount of block sequences and an enhanced acid catalytic effect. The acrylate sidegroups are much more stable than the acetate groups, and are similar in stability to the main hydrocarbon chain. The BA decomposition results in carboxylic and anhydride groups. Decarboxylation also occur and increases with the thermal treatment. In LDPE and EBA the increase in unsaturation is small and mainly due to vinyl end groups formed via β‐cleavage or disproportionation. In EVA the formation of vinyl end groups is suppressed.

Field test results for the 6 MW Carrizo solar photovoltaic power plant

Abstract Testing of subgroups, trackers, and laminates was performed at the Carrizo Solar Photovoltaic Power Plant. Testing was performed to characterize the effects of ethylene vinyl acetate (EVA) degradation at the plant. EVA degradation is believed to have been accelerated by the high operating temperatures accompanying the use of mirrors to concentrate sunlight. Testing of 128 laminates revealed that degradation is highly non-uniform. Measured laminate peak power values ranged from 8.6 W to 47.8 W with an average value of 32.6 W. This average was 35.9% below the installed laminate rating at similar conditions. Mismatch between laminates contributed an additional power loss of 11.1%. Mismatch was found to increase with laminate temperature. One tracker was tested with and without mirror enhancement. It produced 3046.5 W with mirrors and 3275.9 W when the mirrors were covered. Preliminary results indicate that removal of the mirrors would increase the plant's peak power output on hot days.