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The lifetime of industrial polymer products is in many cases limited by aging. Therefore, it is necessary to develop a fast and sensitive method to detect polymer aging at an early stage. A commercially available 50-µm-thick and transparent polyethylene terephtalate (PET) film was aged under different artificial conditions, and the evolution of mechanical properties with increasing aging time was investigated via nanoindentation (NI) and tensile testing. Chemical aging was studied with gel permeation chromatography (GPC), and physical aging was monitored by the first heating of differential scanning calorimetry. NI data evaluated with the method of Oliver and Pharr was compared to tensile test data with good agreement between the results on the macro- and nanoscales. Furthermore, a correlation between NI creep data and GPC data was obtained, which indicates that the aging of the PET films primarily originated from chemical aging. This study states that NI is an appropriate method to determine degradation of PET at an early stage.

To improve the efficiency of bifacial photovoltaic modules, the idea of light deflection was addressed. A thin film with an intended structure was applied in the space between the cells. Due to the selected structural geometry, unused light is specifically redirected to the solar cell and can be absorbed by it and converted into additional current. The effect of the light-directing film was both simulated and measured. Single PV modules without and with commercial structured films or white back sheet were measured to evaluate the results The expected gain of up to 11% from the simulation could not be achieved by measurement, by reaching about 3%.

A comprehensive understanding of failure modes of solar photovoltaic (PV) modules is key to extending their operational lifetime in the field. In this review, first, specific failure modes associated with mature PV technologies, such as crystalline silicon (c-Si), copper indium gallium selenide (CIGS) and cadmium telluride (CdTe), are framed by sources of specific failure modes, their development from the early-developmental stages onwards and their impact upon long term performance of PV modules. These failure modes are sorted by both PV technology and location of occurrence in PV modules, such as substrate, encapsulant, front and rear electrode, absorber and interlayers. The second part of the review is focused on emerging PV technologies, such as perovskites solar cells, dye sensitised and organic PVs, where due to their low to medium technology readiness levels, specific long-term degradation mechanisms have not fully emerged, and most mechanisms are only partially understood. However, an in-depth summary of the known stability challenges associated with each emerging PV technology is presented. Finally, in this paper, lessons learned from mature PV technologies are reviewed, and considerations are given in to how these might be applied to the further development of emerging technologies. Namely, any emerging PV technology must eventually pass industry-standard qualification tests, while warranties for the lifetime of modern c-Si-based modules might be extended beyond the existing warranted life of 25 years.

Nanoindentation (NI) is a contact method to investigate localized micromechanical properties of materials, whereby NI of semi-crystalline polymers is challenging. The influence of morphological str...

The paper provides a comprehensive overview of possible strategies for the repair of cracked polyamide‐based backsheets. A repair process has been developed that comprises the following steps: (i) cleaning, (ii) pretreatment, and (iii) repair process (crack filling and sealing). The important topic of long‐term reliability is still under investigation. Two different repair strategies have been addressed in this article: (i) repairing damage by restoring electrical insulation properties and (ii) preventing further growth of the surface near microcracks. From a technical point of view, several of the repair solutions examined met the defined requirements for compatibility and applicability. On the one hand, repair tapes/films sealed the surface and only covered the cracks. The adhesive did not penetrate into the cavities that had opened through the cracks in the backsheet material. Therefore, adhesive tapes/films are not suitable for the repair of large‐scale damage and the permanent restoration of the electrical insulation properties. On the other hand, several repair coatings based on polyurethane, epoxy, silicone and synthetic rubber were identified which, after a two‐step application process, showed complete crack filling and sealing of the surface. The required insulation resistance of the aged modules could be restored. Since the new and artificial reliability tests are still running, no final conclusions on the long‐term behavior of the repair and its life‐extending effect of PV modules can be drawn at the moment.

Delamination is one of the most critical failure modes of a PV module during service lifetime. Delamination within a backsheet primarily imposes a safety risk, but may also accelerate various other PV module degradation modes. The main aim of this paper is to present a peel test set-up, which is more practical in sample preparation and execution than the width-tapered cantilever beam test and overcomes some issues of standard peel tests like the influence of sample geometry and energy dissipation through deformation on the peel test results. The best results with respect to accuracy and effort were achieved by using a 180° peel geometry where an additional adhesive tape is applied to the peel arm in order to avoid plastic deformation or breakage. The additional support of the adhesive tape leads to comparable peel strength values without any influence of the plastic deformation behavior of the peel arms with different thickness.

A better understanding of moisture ingress in photovoltaic modules is crucial for better predictions of their long-term behavior in the field. Current calculations and simulations of moisture uptake in photovoltaic modules are based on the Fickian diffusion model in a homogeneous material. In this article, in situ humidity measurements in four different encapsulants exposed to transient humidity conditions are compared with Fickian simulations. It is found that the model cannot accurately describe the measured moisture ingress and egress curves. Thus, a new model for finite-element simulations based on two transport mechanisms is applied. The mesh is split into two regions, where channels with a high diffusion coefficient lead through a bulk with a low diffusion coefficient. The diffusion in both regions as well as the flow between them is simulated as Fickian. The new model is able to predict the measured ingress and egress curves more accurately than the Fickian model in all four encapsulants. The same simulation parameters can accurately describe ingress for various relative humidity values between 20% and 80%, as well as egress from 40% to 20%. This allows further prediction of moisture ingress after the measurement of a single ingress curve and a corresponding parameter optimization. However, a nonlinearity of the diffusion during egress at higher moisture values in the encapsulants is found.

The ageing behavior of ethylene vinyl acetate as encapsulant material in photovoltaic modules has been extensively studied over the years. This study aims to make a step forward in understanding how environmental conditions influence polymer behavior, how different module components interact with each other and finally how (and if) it is possible to correlate changes between material properties and power output. In this work, performances of laminated mini-modules subjected to different artificial ageing tests are compared and the degradation behavior of EVA is investigated. In particular, qualitative analysis of additives, color changes as well as changes in chemical structure and thermal stability of the encapsulant are analyzed.

This study presents aging of backsheet materials that were stored for 17 years in the dark at room temperature. The material properties were measured and compared to the results from right after production. After 17 years of storage the strain at break values decreased significantly for all materials. As chemical aging phenomena were excluded, a disentanglement of the polymer chains in the amorphous phase would explain the observed changes. Especially for PVDF the change in the mechanical behavior is considered as very critical and possibly would lead to cracking during operation.

Within this paper an overview on possible repair solutions for cracked polyamide backsheets is presented. A repair procedure was developed including the following steps: (i) cleaning, (ii) pre-treatment and (iii) repair process (crack filling and sealing). The procedure was tested in the laboratory and in the field, the important topic of long-term reliability under natural and artificial weathering is still under investigation. Damage repair with restoration of electrical insulation properties and prevention of further growth of surface near microcracks have been addressed in this work. Several of the investigated repair solutions fulfilled the defined requirements regarding compatibility, applicability, crack filling and sealing of the surface.

During their outdoor service, photovoltaic (PV) modules are exposed to different set of external stresses that can affect their efficiency and lifetime such as UV irradiation, temperature and humidity cycles, rain, snow and wind loads, hail, sand and/or salt. Moreover, internal stresses such as choice of materials and design (additives, morphology and compatibility of materials) can drive degradation of PV modules as well. The failure data collection started already in 1980s and is still ongoing. Most of these studies are focused mainly on power data or categorizing PV failure modes concerning solely climate, EVA or cell-technology. However, relationship between climate, degradation of polymeric materials and degradation of PV modules has not been reported so far. Hence, within this study a lot of effort was put into finding the appropriate data and publications with as many as possible data on PV, climate and materials degradation. As a result, a great overview of climate and polymeric materials induced PV failure modes is given. Based on the reported data, the topic of new, climate-based design of PV modules is discussed. This paper provides numerous number of selected references that can be beneficial in further studies on degradation of PV modules, design of PV modules and choice of materials.

The main focus of this work is to investigate the degradation behavior of two newly developed encapsulants for photovoltaic applications (thermoplastic polyolefin (TPO) and polyolefin elastomer (POE)), compared to the most widely used Ethylene Vinyl Acetate (EVA) upon exposure to two different artificial ageing tests (with and without ultraviolet (UV) irradiation). Additive composition, optical and thermal properties and chemical structure (investigated by means of Thermal Desorption Gas Chromatography coupled to Mass Spectrometry, UV-Visible-Near Infrared spectroscopy, Differential Scanning Calorimetry, Thermogravimetric Analysis and Fourier Transform-Infrared spectroscopy, respectively) of the analyzed polymers were monitored throughout the exposure to artificial ageing tests. Relevant signs of photo-oxidation were detectable for TPO after the UV test, as well as a depletion of material&rsquo, s stabilizers. Signs of degradation for EVA and POE were detected when the UV dose applied was equal to 200 kW h m&minus, 2. A novel approach is presented to derive information of oxidation induction time/dose from thermogravimetric measurements that correlate well with results obtained by using oxidation indices.

Instrumented nanoindentation (NI) was used to examine the viscoelastic properties of poly(methyl methacrylate) (PMMA) as an amorphous polymer model. An evaluation combining adhesive contact and empiric spring–dashpot models has been applied to obtain the instantaneous elastic modulus E 0 and the infinitely elastic modulus E ∞ from nanoindentation creep curves. The value of E 0 has been compared to moduli obtained with atomic force microscopy-based nanoindentation (AFM-NI) and compression tests. Furthermore, the elastic modulus has been evaluated by the method introduced by Oliver and Pharr ( O & P ) for the NI and AFM-NI results. Comparison of the elastic modulus E 0 from the creep measurements of NI and AFM-NI to compression tests reveals good agreement of the results. However, only the O & P based AFM-NI results yield to lower values.

This paper describes the production of a high-performance composite with a bio-based carbon content of 100 %. The material is based on epoxidized linseed oil (cured by crystalline citric acid) and flax fiber reinforcement and manufactured via hand layup followed by vacuum bagging. Specific focus is on evaluating the effect of fiber moisture on the thermoset's chemical structure and the overall composite's morphology and mechanical characteristics. Pre-drying of the fibers is shown to be essential in order to maximize the composite's performance. The inherent fiber moisture content (∼8 wt.%) adversely affects the resin's curing reaction and moreover causes a significant porosity within the composite (resulting from water vaporization and hindered consistent impregnation).

The very strict purity requirements of polymer parts that are used in the semiconductor manufacturing industry lead to an excessively low yield rate. To decrease the costs in the production chain, detailed knowledge about possible impurities during each processing step is essential. This work provides an overview of non-destructive testing techniques that are capable of either detecting or even identifying these impurities. The most promising techniques were then combined in a semi-automatized laboratory demonstrator that can be used as an in-line diagnostics tool to prevent processing of faulty parts. Results from these measurements are presented and discussed.

To contribute to the targeted 10 million tons per year of recycled plastic in Europe by 2025 and to improve the mechanical sorting degree of polyethylene (PE) products, density prediction models were developed from Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and Raman spectroscopic data. State-of-the-art sorting in mechanical recycling provides separated polymer classes, however an improved classification with specific chemical and physical features such as density or melt flow rate has not been developed yet. Applying multivariate data analysis (MVDA) on the spectral datasets of 10 different PE materials, one FTIR-ATR and two Raman spectra based partial least square (PLS) density models were developed. However, whereas all three models are applicable to predict PE density accurately, the Raman models have shown some advantages. Firstly, less principle components (PC) are needed and secondly the density can be assessed with higher accuracy, due to the more robust cross-validated PLS model. Moreover, the obtained PC-s indicate that in the FTIR-ATR model the CH3/CH2 ratio, while in the Raman model the CH2, CH and the crystalline C–C bands can be correlated with the PE density. The most accurate PLS model was obtained from the 1500-1000 cm−1 Raman shift region. The developed models could improve the density based mechanical separation of PE and consequently increase the quality of recycled and reprocessed PE products.

An efficient UV-irradiation process plays an important role for a successful pickup of very thin (

Due to the general price pressure PV modules experienced in the last decade, a variety of alternative polymer materials and new backsheet designs were developed and introduced into the market, amongst others also extruded backsheets based on polypropylene (PP). The production of co-extruded films represents a backward integration of backsheet manufacturers, allowing for easy material and design modifications regarding additive formulation, fillers and geometry. The main objective of this paper was to describe the influence of the special properties of PP-based backsheets on the performance and reliability of PV modules. The higher reflectance of the PP backsheet compared to a reference polyester (PET) based laminate led to an increase in power output between 1.5 and 2.5%. Test modules using PP and PET backsheets were exposed to 3000 h of damp heat testing. No changes in power output for either of the test modules was observed. However, the selective permeation properties of PP backsheets prevent humidity from entering the module (similarly to PET based backsheets) but allow for significantly higher diffusion of acetic acid out of the PV module. Therefore, in contrast to test modules using Ethylene Vinyl Acetate (EVA) encapsulants and PET backsheets, no silver grid corrosion was observed for modules using PP backsheets. Co-extruded backsheets based on PP show great potential to be a valid replacement of standard PET based backsheets in PV modules. On the one hand, the PP backsheet so far proved excellent stability, exhibiting no severe material degradation after extended exposure to temperature, humidity and irradiation. On the other hand, its improved functional properties (optical properties; selective permeability) lead to increased performance and improved long-term stability of the tested PV modules.

A broad spectrum of commercially available technical biopolymers is screened with respect to applicability as absorber materials in solar collectors. Technical biopolymers nominated as potentially suitable (bio-polyamide, poly(lactic acid), cellulose acetate, cellulose acetate butyrate, poly(trimethylene terephthalate)) are characterized in detail and in particular with regards to their application relevant aging behaviour. Candidate materials are subjected to various exposure conditions (in water at 35 °C and 80 °C, in air at 60 °C, 70 °C and 80 °C and to the Xenontest – depending on potential collector type) for up to 1000 h. Continuously both application relevant and aging-indicative properties such as thermal, mechanical and morphological characteristics are analysed. Consequently property changes and underlying aging mechanisms are discussed. Based on these results potential application opportunities of the materials are considered. Concisely, the study reveals a high potential of technical biopolymers for solar thermal applications.

Acetic acid, which is formed during degradation of the most frequently used photovoltaic (PV) encapsulant ethylene vinyl acetate (EVA), is linked to several PV module failure mechanisms like corrosion of interconnectors, cells or potential induced degradation (PID). An evaluation of a new measurement technique and data analysis for acetic acid permeation through photovoltaic backsheet films is described. The influence of the layer composition of the multilayer backsheets on the acetic acid permeation rates (AATR) was determined by investigating the permeation properties of the individual layers as well as the whole polymeric multilayer composites. Various polymeric backsheet types based on PET-core layers showing a very high barrier for acetic acid permeation were compared to fully polyamide material stacks which allow for a much higher transmission of acetic acid through the backsheet out of the module. Incorporated Al-layers were found to not affect the AATRs of PET based backsheets.

The purpose of this work was the investigation of the influence of the microclimate on the ageing behavior of polymeric encapsulants for photovoltaic (PV) modules. Different types of encapsulation films were investigated. Single film and laminated samples were artificially aged under different conditions (with and without irradiation). The results showed that there is a strong influence of the microclimate on the aging behavior of polymeric encapsulant materials on the optical, chemical and morphological properties of the materials. Differences were even detectable in the unaged state between film and module samples after the production process. Not only has the sample set-up (film or laminated module sample) highly influenced the degradation of the encapsulants, but also the type of aging (dark aging or aging with irradiation).

COST Action entitled PEARL PV aims at analyzing data of monitored PV systems installed all over Europe to quantitatively evaluate the long-term performance and reliability of these PV systems. For this purpose, a data bank is being implemented that can contain vast amounts of data, which will enable systematic performance analyses in combination with simulations. This paper presents the development process of this data bank.

In order to model PV module degradation effects, it is necessary to understand them not only on a macroscopic level by monitoring the power loss, but also to investigate the underlying processes at the molecular level. In most cases the encapsulation and backsheet films play a major role in PV module degradation. Some failure modes like browning are directly related to the encapsulation film. But in most cases material interactions are the main root cause for PV module degradation. For example, acetic acid, which is a degradation product of ethylene vinyl acetate (EVA), not only causes corrosion of the PV ribbons and the grid fingers, but also promotes potential induced degradation or delamination. Furthermore it accelerates the oxidation process of EVA itself. Also, the type of backsheet influences many degradation mechanisms by its barrier properties against water vapor (WVTR), oxygen (OTR), and acetic acid (AATR). High concentrations of especially water vapor and acetic acid in the PV module accelerate nearly all degradation modes. PV module failure modes are described very well in the literature, including its main driving factors. Also the right combination of encapsulant and backsheet film can be beneficial. Nevertheless there are no common rules or acceleration factors which apply generally for all silicon PV module architectures. On the one hand the degradation modes depend on the bill of materials and components and are unique for each single PV module composition. On the other hand usually several degradation processes are running simultaneously and may have synergistic or antagonistic effects, making it difficult to correlate observed effects with single processes. In this chapter the focus is given on the properties and the degradation behavior of encapsulation materials, most prominently to EVA, and its influence on the long term reliability of PV modules.

This paper describes the development of a novel high-performance thermoset based on epoxidized linseed oil and pure crystalline citric acid (CA). Fully bio-based polymer networks are generated and CA is shown to be a very efficient hardener for epoxidized plant oils. Comprehensive processing-structure-property relationships are established and optimum curing parameters are derived. The thermoset's polymer physical property profile (incl. high stiffness and strength) reveals its great potential to substitute petrochemical based resins.

In photovoltaics, the quality of the polymeric solar cell embedding material is of key importance for the long-term durability and performance of the PV modules. For the most common encapsulant, elastomeric ethylene vinyl acetate (EVA), the degree of crosslinking is a key issue in this respect. Raman spectroscopy was researched as a fully contact-free, truly non-destructive optical method to measure the degree of EVA crosslinking of bare EVA film samples as well as in-situ inside assembled PV modules. The method relies on evaluating subtle but characteristic spectral differences in the CH-stretching vibration region (3.000–2.800 cm −1 ) that correlate directly, unambiguously and reliably to the crosslinking state of the EVA encapsulant. With measurement times below one second per analysis point, the method is suitable for real-time, in-line quality control. Using a self-referencing data evaluation approach, the method could be designed to be widely immune to real-world effects, including different sample reflectivity and instrument drifts. Involving the reaction kinetics of the curing reaction, the Raman data can be converted into crosslinking readings that equal the traditional, Soxhlet-derived gel content values. The method has been successfully validated for bare foils, glass–backsheet and glass–glass modules with three different EVA types and deployed in-line in a commercial PV module manufacturing line. Using Raman spectroscopy, it is thus possible to determine the degree of crosslinking of the EVA encapsulant inside assembled modules in-line and with high accuracy, even on moving modules.