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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.

Zusammenfassung Hintergrund Das chirurgische Aufklärungsgespräch stellt eine komplexe Herausforderung dar und ist als Lernziel im Nationalen Kompetenzbasierter Lernzielkatalog Medizin verankert. Die wenigen bestehenden Lehrformate sind uneinheitlich und aufwändig; insbesondere juristische Implikationen nehmen im Studium wenig Raum ein, obwohl sie mit Inkrafttreten des Patientenrechtegesetzes vermehrt in den Fokus gerückt sind und u. a. bei Regressverfahren eine wichtige Rolle spielen. Ziel der Arbeit Ziel war eine Ermittlung des Wissensstandes von Medizinstudierenden zu den rechtlichen Aspekten des chirurgischen Aufklärungsgespräches auf Basis einer juristischen Analyse des Patientenrechtegesetzes. Dieses wurde auf Implikationen für die Lehre im Medizinstudium überprüft. Material und Methoden Nach Analyse von Gesetz und Rechtsprechung wurden Multiple-Choice-Fragen zu den rechtlichen Aspekten des chirurgischen Aufklärungsgespräches erstellt und im Sinne einer Querschnittsanalyse im Progress Test Medizin platziert. Es erfolgte die deskriptive statistische Auswertung der Ergebnisse bei Berliner Medizinstudierenden. Ergebnisse Es wurden die Antworten von 2625 (Wintersemester 2018/19) und 2409 (Sommersemester 2019) Berliner Studierenden ausgewertet. Bei den Fragen zur Art aufzuklärender Prozeduren sowie der Bedenkzeit nahm die Anzahl Studierender, die die Frage korrekt beantwortete, über die Zeit zu, erreichte jedoch nicht den Vergleichswert aller Fragen des Progress Test Medizin. Bei den Fragen zu den notwendigen Inhalten wählten, unabhängig vom Ausbildungsstand, zwischen 30 und 60 % die korrekte Antwort, eine Zunahme korrekter Antworten über die Zeit war nicht zu sehen. Diskussion In der vorliegenden Arbeit konnte gezeigt werden, dass bei Medizinstudierenden über alle Semester hinweg Unsicherheiten bezüglich der juristischen Aspekte des Aufklärungsgespräches bestehen. Der gesetzliche Rahmen lässt allerdings Raum für neue Lehrformate wie der hier erstmals vorgestellten „Co-Aktion“: der Studierende führt die Aufklärung eines Patienten selbstständig, unter Aufsicht und Verantwortung des behandelnden Arztes, durch.

Since 2010, the ultraviolet fluorescence (UVF) method is used to identify defects in wafer-based crystalline silicon photovoltaic (PV) modules. We summarize all known applications of fluorescence imaging methods on PV modules to identify defects and characteristics. The aim of this review is to present the basic principles for the interpretation of UVF images. The method allows for detection of cell cracks in a chronological order of occurrence, visualizing hot parts in a PV module, and identifying deviating bill of materials of PV modules. The effects of various material combinations on the UVF are reproduced in the lab and explained for the first time. Seasonal effects on the UVF are presented for the first time. In addition, some not yet understood features in the images are shown and discussed. Furthermore, the application of UVF imaging for manual, hood-based, and drone-based inspection is presented. The analysis speed of the three methods has been measured under real conditions. For the manual inspection, we found an evaluation speed of 250 modules/h, for a hood-based system 200 modules/h and the drone-based method allows an imaging speed of up to 720 modules/h.

8th World Conference on Photovoltaic Energy Conversion; 477-479, A major component in the growth of developing PV markets around the world is the reliability and longevity of photovoltaic (PV) modules. The polymeric encapsulation materials' chemical and physical stability directly affects reliability. Ultraviolet Fluorescence (UVF) imaging is a technique that can detect the impacts of the polymeric encapsulant's aging directly on site at a PV plant. This research focuses on advanced imaging analysis of UVF pictures and the subsequent correlation to electrical characteristics of PV modules that have undergone longterm, accelerated aging processes particular to a certain climate. For establishing a correlation, a so called UVF area ratio was established, resulting from the typical fluorescence patterns of the encapsulant material, which arise due to stress impact (e.g.: water vapor ingress, elevated temperature, irradiation) and aging/degradation processes. The results of the data analysis demonstrate a distinct correlation between the electrical parameters and the UVF area ratio with increasing aging time. Long-term test series with different climate-specific aging processes confirm UVF area ratio correlations with power and series resistance. Hence, calculating the UVF area ratio can be used to predict the service life and electrical power dissipation of individual PV modules within a PV array, under the assumptions of the utilization of the same kind of polymeric encapsulation and backsheet materials and a similar climate.

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.

The research project INFINITY focuses on design improvements for PV system components operating in different climatic regions. This topic gained pertinence in recent years due to increased installation rates worldwide with the highest growth rates in non-moderate climates. As PV components are not optimized to the respective climate zone, the target of the project is to gather failure data from PV installations in various climate zones. A standardized data input was achieved by using an extended format of the IEA PVPS Task 13 failure survey, allowing to enter PV system and failure information in rich detail. The components' and failure structure were elaborated by combining input from reliability workshop proceedings, PVPS Task 13 and project partners' experience in PV reliability testing. These structures were mapped into a database to collect and prepare the input for further statistical analysis. Collected data was filtered, offering a tidy data set of 1048 samples from 340 sub-systems from 45 countries worldwide. After data filtering, a power loss evaluation, a cluster analysis and a trend analysis were performed. This paper presents results of comparing PV module failures in different climate zones starting with a range of PV systems installed in the 1970s, to recently installed systems.

Over the last years, the development of innovative, fast and non-destructive characterisation techniques for the detection of PV-module failures and advanced analysis of yield losses in photovoltaic power plants has become a key challenge in scientific research. Besides standard on-site thermographic screening, several novel and easily applied methods were developed and successfully tested. They differ mainly in their possible field of application, their applicability in the detection of different failure types and their cost of setup and operation. In order to evaluate the boundary conditions of application for the various methods, different defective PV-modules were comparatively investigated with commercially available and innovative outdoor analysis methods. The results were evaluated with regard to error detection rate and economics. Based on this comparison, efficient operation and maintenance (O&M) measures for early and general failure detection within large power plants can be deducted.

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.

Obtaining informed consent is a challenging task and is part of the educational objectives in the German NKLM. Teaching formats are inconsistent and time-consuming, with little emphasis on legal aspects, although they have moved into the focus of attention since the implementation of patient rights laws and play an important role in legal proceedings.The aim of this study was the evaluation of medical students' knowledge about the legal aspects of obtaining informed consent. A legal analysis was performed, and the patient rights laws were reviewed with reference to implications for undergraduate medical education.After the analysis of laws and jurisdiction, multiple-choice questions regarding the legal aspects of obtaining informed consent were created and placed in the Progress Test Medicine (PTM). A statistical analysis of the results of Berlin medical students was performed descriptively.The answers of 2625 (winter semester 2018/19) and 2409 (summer semester 2019) medical students in Berlin were analyzed. The rate of students who answered the questions about the procedures requiring informed consent and adequate time for consideration increased over time but did not reach comparable values to all PTM questions. Questions about required content were answered correctly by 30 to 60% of the students, regardless of their level of training; we did not see an increase along with the time of study.In our study, we were able to show that medical students of all educational levels show tentativeness when it comes to the legal aspects of obtaining informed consent. Yet, the legal framework offers room for new teaching formats like "Co-Action", introduced in this paper for the first time, where students acquire informed consent while being supervised by the medical doctor in charge.HINTERGRUND: Das chirurgische Aufklärungsgespräch stellt eine komplexe Herausforderung dar und ist als Lernziel im Nationalen Kompetenzbasierter Lernzielkatalog Medizin verankert. Die wenigen bestehenden Lehrformate sind uneinheitlich und aufwändig; insbesondere juristische Implikationen nehmen im Studium wenig Raum ein, obwohl sie mit Inkrafttreten des Patientenrechtegesetzes vermehrt in den Fokus gerückt sind und u. a. bei Regressverfahren eine wichtige Rolle spielen.Ziel war eine Ermittlung des Wissensstandes von Medizinstudierenden zu den rechtlichen Aspekten des chirurgischen Aufklärungsgespräches auf Basis einer juristischen Analyse des Patientenrechtegesetzes. Dieses wurde auf Implikationen für die Lehre im Medizinstudium überprüft.Nach Analyse von Gesetz und Rechtsprechung wurden Multiple-Choice-Fragen zu den rechtlichen Aspekten des chirurgischen Aufklärungsgespräches erstellt und im Sinne einer Querschnittsanalyse im Progress Test Medizin platziert. Es erfolgte die deskriptive statistische Auswertung der Ergebnisse bei Berliner Medizinstudierenden.Es wurden die Antworten von 2625 (Wintersemester 2018/19) und 2409 (Sommersemester 2019) Berliner Studierenden ausgewertet. Bei den Fragen zur Art aufzuklärender Prozeduren sowie der Bedenkzeit nahm die Anzahl Studierender, die die Frage korrekt beantwortete, über die Zeit zu, erreichte jedoch nicht den Vergleichswert aller Fragen des Progress Test Medizin. Bei den Fragen zu den notwendigen Inhalten wählten, unabhängig vom Ausbildungsstand, zwischen 30 und 60 % die korrekte Antwort, eine Zunahme korrekter Antworten über die Zeit war nicht zu sehen.In der vorliegenden Arbeit konnte gezeigt werden, dass bei Medizinstudierenden über alle Semester hinweg Unsicherheiten bezüglich der juristischen Aspekte des Aufklärungsgespräches bestehen. Der gesetzliche Rahmen lässt allerdings Raum für neue Lehrformate wie der hier erstmals vorgestellten „Co-Aktion“: der Studierende führt die Aufklärung eines Patienten selbstständig, unter Aufsicht und Verantwortung des behandelnden Arztes, durch.

In the last decade and longer, photovoltaic module manufacturers have experienced a rapidly growing market along with a dramatic decrease in module prices. Such cost pressures have resulted in a drive to develop and implement new module designs, which either increase performance and/or lifetime of the modules or decrease the cost to produce them. In this paper, the main motivations and benefits but also challenges for material innovations will be discussed. Many of these innovations include the use of new and novel materials in place of more conventional materials or designs. As a result, modules are being produced and sold without a long-term understanding about the performance and reliability of these new materials. This has led to unexpected new failure mechanisms occurring few years after deployment, such as potential induced degradation or backsheet cracking. None of these failure modes have been detected after the back then common single stress tests. New accelerated test approaches are based on a combination or sequence of multiple stressors that better reflect outdoor conditions. That allows for identification of new degradation modes linked to new module materials or module designs.

We describe the process and outcome of our efforts to port a legacy Fortran benchmark code to heterogeneous GPU-accelerated computing architectures using OpenMP. The benchmark code is one of the multi-zone NAS Parallel Benchmarks (NPB-MZ) called SP-MZ. This “mini-app” mimics the computation and data movement that is found in popular legacy and modern implicit computational fluid dynamics (CFD) solvers. Our objective was to examine how efficiently legacy Fortran codes can be ported to accelerators by leveraging OpenMP directives. We describe the development and optimization process and demonstrate the performance impact of various code modifications. We show select profiling results from the NVIDIA Visual Profiler (nvpp) to help others diagnose and overcome performance issues in their own applications. We present results for two compute systems endowed with NVIDIA V100 accelerators.

Photovoltaic modules can experience damages of varying severity in the case of heavy hail storms. In theworst case, complete glass and solar cell breakage results in efficiency and security losses of the affectedmodules which therefore have to be replaced. However, there is a strong need to inspect the remainingmodules directly in the field in order to assure no hidden damage. Three hail-affected photovoltaic plantsin the south of Austria were investigated first with common standard methods like analysis of the plantmonitoring data and thermography. Then, these plants were additionally investigated by novel nondestructivemethods. With the aid of two innovative characterisation tools, outdoor electroluminescenceand UV-fluorescence imaging, hail-induced damaging of solar cells can be detected even when thesolar glass of the modules withstood the mechanical impact of the hailstorm and no damages are visibleto the naked eye or well recognizable by thermography. The non-destructive, easy to handle and fastcharacterization technique UV-fluorescence imaging allows the detection and visualisation of hailinduced cell damage. Modulesshowing partial cell breakage and/or micro cracks e as proven by outdoorelectroluminescence measurements e and lead to a reduced electrical performance can be unequivocallyidentified.&nbsp

The glossy appearance of the cover glass of a photovoltaic module is mainly responsible for giving the module a mirroring effect, which is often disturbing in the case of building integrated photovoltaic (BIPV) façade applications. In this work, an innovative approach is presented to reduce the glare of BIPV modules by applying surface coatings to the front glass of the module. Three different glass coating technologies, applied on the outer surface of the photovoltaic module, were investigated: inkjet printing, screen printing, and sol-gel spray coating. The coatings, applied by these technologies in three different colours (grey, anthracite, and terracotta), were characterized with respect to their adhesion, light transmission, and reflection. Their chemical and physical stability after stress impact (condensed water resistance and chemical resistance against acids and salt-fog) was also investigated. The durability of these coatings was further evaluated after performing environmental simulations with artificial sunlight (xenon weathering) on coated glass. Additionally, accelerated aging tests (damp-heat testing, temperature cycling) were performed on the test modules to assess their performance stability. For those coatings, where no stress-induced changes in colour or the optical appearance of the module surface were detected, the potential for the architectural integration of the modules into building facades is high. A minimum glare of less than 0.1% of the specular reflection could be achieved. On the basis of the results of the optical characterization and the durability tests, grey screen-printed BIPV solar modules were installed in a demonstrator test façade. The high electrical performance, resulting in only a 10–11% performance decrease compared to the noncoated reference modules, perfectly showed the suitability of screen-printing in future applications for coloured and glare-reduced BIPV installations.

When dealing with building integrated photovoltaics aesthetical aspects have to be considered. In particular for facade integrated modules with crystalline Silicon (c-Si) solar cells alternative colors are demanded. In this paper an approach for tuning the color of standard c-Si solar cells is presented relying on plasmonic coloring. Metallic (Ag) nano-particles with a diameter of around 100 nm were created on the surface of standard c-Si solar cells. At those nano-particles plasmonic scattering at around 450 to 550 nm causes a color change from blue to green. The green color is resulting from plasmonic scattering and it is found to be insensitive to the angle of observation. A performance analysis of the c-Si cells before and after coating shows that the power of the cells is decreased by less than 10% when applying the plasmonic coating. A first test module comprising of plasmonic-green c-Si cells was carefully characterized and mounted at a test facade for building integrated modules in order to generate data in the targeted field of application. First results of the test module demonstrate that plasmonic coloring is a feasible approach to tune the color of standard c-Si solar cells for being applied in building integrated photovoltaics.

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.

A number of surface tension models have been implemented in a 3D multi-physics multi-material code, ALE–AMR, which combines Arbitrary Lagrangian Eulerian (ALE) hydrodynamics with Adaptive Mesh Refinement (AMR). ALE–AMR is unique in its ability to model hot radiating plasmas, cold fragmenting solids, and most recently, the deformation of molten material. The surface tension models implemented include a diffuse interface approach with special numerical techniques to remove parasitic flow and a height function approach in conjunction with a volume-fraction interface reconstruction package. These surface tension models are benchmarked with a variety of test problems. Based on the results, the height function approach using volume fractions was chosen to simulate droplet dynamics associated with extreme ultraviolet (EUV) lithography.

We present a highly scalable demonstration of a portable asynchronous many-task programming model and runtime system applied to a grid-based adaptive mesh refinement hydrodynamic simulation of a double white dwarf merger with 14 levels of refinement that spans 17 orders of magnitude in astrophysical densities. The code uses the portable C++ parallel programming model that is embodied in the HPX library and being incorporated into the ISO C++ standard. The model represents a significant shift from existing bulk synchronous parallel programming models under consideration for exascale systems. Through the use of the Futurization technique, seemingly sequential code is transformed into wait-free asynchronous tasks. We demonstrate the potential of our model by showing results from strong scaling runs on National Energy Research Scientific Computing Center’s Cori system (658,784 Intel Knight’s Landing cores) that achieve a parallel efficiency of 96.8% using billions of asynchronous tasks.

As photovoltaics shows a large growth potential in climatic-sensible regions, specific artificial ageing test procedures are required for an efficient and reliable development of new PV module designs, components and materials optimized for the use in these future markets. A program was worked out with 10 specific stress combinations for accelerated ageing tests simulating tropical, arid, moderate and alpine climates as well as additional environmental factors like snow and wind-load, salty atmosphere or large temperature fluctuations. The accelerating effect of enhanced temperature, humidity and/or irradiation on the degradation of materials and consequential on the power output could be shown. Additional mechanical load and temperature cycling gave rise to breakage of interconnectors and cells. The failures and performance losses observed in PV-plants installed in various climate zones worldwide are compared to the failure modes and degradation effects detected upon climate specific accelerated aeging testing.

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.

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.

Since the beginning of PV module production, Soxhlet extraction has been the standard method for the determination of the gel content and the resulting calculation of the degree of crosslinking of the most common PV encapsulant ethylene vinyl acetate (EVA). While the method is deemed well established and several pertinent ASTM and ISO standards exist, in practise the actual procedures used in – and trusted by – both industry and R&D institutions vary substantially. To evaluate the reliability of the methods and the comparability of the results, a round-robin test involving seven independent European laboratories – one industrial PV module manufacturer and six R&D facilities – was conducted. The measurements were performed using homogenous, anonymized sample sets, each comprising five differently crosslinked EVA foils. The analysis showed that results obtained for the same samples may deviate significantly, but also that very different analytical procedures can yield comparable values. In a systematic study, the impact of various key parameters of the analytical process (extraction time and solvent, drying conditions, sample size and weight etc.) was investigated. Based on these findings, deviations observed in the round-robin study could be linked to their origins and the main pitfalls were identified. In conclusion, a suggestion for an optimised standard procedure was derived to ensure comparable results at all laboratories.

The weathering stability of polymeric backsheets is very important for the reliability of photovoltaic (PV) modules. In addition to reliability, cost reduction and sustainability are upcoming challenges the PV backsheet industry is facing with. The most commonly used material for PV backsheets is poly(ethylene-terephthalate)-PET. However, PET is in general very sensitive to hydrolysis, which leads to chain scission and causes embrittlement, cracking, delamination, and dimensional instability of the backsheet. Compared to that newly developed modified polyolefin backsheets have favorable selective permeation properties and high mechanical flexibility, which could be key properties for backsheets in terms of higher PV module reliability. In this work, the weathering stability of PET/fluoropolymer backsheet and an alternative coextruded polyolefin-backsheet was investigated in terms of thermal and mechanical stability. Both materials were artificially aged and the changes caused by aging were investigated. The polyester-based backsheet showed embrittlement and reduced elongation at break for 70%. The polyolefin-based backsheet retained its mechanical flexibility even after 2000 h of aging under damp-heat conditions, with no significant physical or chemical aging processes occurring. The comparison of the results of both backsheets suggests that the polyolefin backsheet is a promising candidate for the reduction of cracks and delamination in the field

Within the last years, an increased occurrence of backsheet cracking, especially of Polyamide-based backsheets, was observed in PV installations and reported in literature. Thus, a detailed failure analysis on cracked polymeric backsheets was performed in order to identify the drivers leading to the unexpected behaviour of the Polyamide multilayer composites. Using a unique combination of analytical tools allowed for deducing a spatially resolved representation of material degradation effects within a PV module for the first time. The correlation of local material degradation effects with the influence zones of external and internal stresses enables the derivation of the main factors for the formation of different types of cracks in Polyamide backsheets.

Several series of six-cell photovoltaic test-modules—intact and with deliberately generated failures (micro-cracks, cell cracks, glass breakage and connection defects)—were artificially and naturally aged. They were exposed to various stress conditions (temperature, humidity and irradiation) in different climate chambers in order to identify (i) the stress-induced effects; (ii) the potential propagation of the failures and (iii) their influence on the performance. For comparison, one set of test-modules was also aged in an outdoor test site. All photovoltaic (PV) modules were thoroughly electrically characterized by electroluminescence and performance measurements before and after the accelerated ageing and the outdoor test. In addition, the formation of fluorescence effects in the encapsulation of the test modules in the course of the accelerated ageing tests was followed over time using UV-fluorescence imaging measurements. It was found that the performance of PV test modules with mechanical module failures was rather unaffected upon storage under various stress conditions. However, numerous micro-cracks led to a higher rate of degradation. The polymeric encapsulate of the PV modules showed the build-up of distinctive fluorescence effects with increasing lifetime as the encapsulant material degraded under the influence of climatic stress factors (mainly irradiation by sunlight and elevated temperature) by forming fluorophores. The induction period for the fluorescence effects of the polymeric encapsulant to be detectable was ~1 year of outdoor weathering (in middle Europe) and 300 h of artificial irradiation (with 1000 W/m2 artificial sunlight 300–2500 nm). In the presence of irradiation, oxygen—which permeated into the module through the polymeric backsheet—bleached the fluorescence of the encapsulant top layer between the cells, above cell cracks and micro-cracks. Thus, UV-F imaging is a perfect tool for on-site detection of module failures connected with a mechanical rupture of solar cells.

The object of this paper is to determine the thermal expansion behavior of nine different encapsulants in order to identify possible deficiencies in production processes and allow for the optimization of the process parameters. High dimensional stability of the encapsulant is of great importance in photovoltaic (PV) module production to avoid problems during lamination and/or in application. For this purpose, the samples were heated twice in a thermo-mechanical analyzer (TMA) in tensile mode, and the coefficient of thermal expansion (CTE) over temperature was evaluated. To get additional information about transition temperatures of the encapsulants, differential scanning calorimetry (DSC) measurements were made. The TMA results for most samples showed anisotropic behavior which was eliminated after the first heating run. Three samples showed shrinkage with subsequent increased thermal expansion as well as anisotropic behavior. It could be shown that knowing the thermal expansion behavior of the solar cell encapsulants is highly relevant for the PV module lamination process, and Thermo-Mechanical Analysis proved to be a suitable method to evaluate and also for quality control of solar cell encapsulation films.

We present a novel method for the solution of the diffusion equation on a composite AMR mesh. This approach is suitable for including diffusion based physics modules to hydrocodes that support ALE and AMR capabilities. To illustrate, we proffer our implementations of diffusion based radiation transport and heat conduction in a hydrocode called ALE-AMR. Numerical experiments conducted with the diffusion solver and associated physics packages yield 2nd order convergence in the L2 norm.

The influence of the type of backsheet on the electrical performance of test modules was evaluated before and after increasing time of accelerated ageing (damp heat [DH] exposure). Besides the measurement of the electrical power of the modules and the performance of the cells by electroluminescence, the ageing-induced changes within the polymeric encapsulate and backsheets were investigated by means of vibrational spectroscopy and by thermo analytical methods. In addition, the permeability of the backsheets in the original and aged state was determined. This wide set of test parameters and methods allowed for the detection of correlations between (i) physical and chemical properties as well as their ageing-induced changes of the materials and (ii) the module performance. A clear dependence of the relative loss in power output upon exposure under DH conditions for 2000 h could be observed for a set of identical test modules varied in composition only in the type of back cover used. While the modules containing gas-tight backsheets and glass experienced only little loss in the relative power output, some modules with permeable backsheets showed a significant relative decrease in the power output and fill factor in dependence of the backsheet type used. Cell degradation could be visualised by recording electroluminescence images before and after the accelerated ageing test. The permeation properties of the backsheet used and their ageing-induced changes seem to have an influence on the module performance. However, the absolute values neither of the water vapour transmission rate (WVTR) nor of the oxygen transmission rate (OTR) are directly linked to the loss in power output upon accelerated ageing under DH conditions. It could be shown that the ageing-induced changes (relative transmission rates) between WVTR and OTR can be correlated with the module performance. These ageing-induced changes in the permeation behaviour of the backsheets can be explained by (i) physical changes (e.g. post-crystallisation, changes in the crystal structure or the crystalline microstructure) and (ii) chemical ageing effects such as a decrease in the molecular mass of the polyester (PET) polymer chains because of hydrolytic polymer degradation leading to a change in the crystallisation behaviour of PET. Hydrolytic degradation (= chemical ageing) of the PET core layer was observed (with varying extent) for all PET-based backsheets and can, thus, not be directly correlated with the loss in performance of the corresponding test modules. The physical ageing effects, however, were detected only for those backsheets showing (i) strong deviating changes in the relative permeation rates for oxygen and water vapour upon accelerated ageing and (ii) a clear loss in electrical performance. Copyright © 2015 John Wiley & Sons, Ltd.

Summary: Loss of heterozygosity (LOH) of the adenomatous polyposis coli (APC) gene triggers a series of molecular events leading to intestinal adenomagenesis. Haploinsufficiency of the cohesin Rad21 influences multiple initiating events in colorectal cancer (CRC). We identify Rad21 as a gatekeeper of LOH and a β-catenin target gene and provide evidence that Wnt pathway activation drives RAD21 expression in human CRC. Genome-wide analyses identified Rad21 as a key transcriptional regulator of critical CRC genes and long interspersed element (LINE-1 or L1) retrotransposons. Elevated RAD21 expression tracks with reactivation of L1 expression in human sporadic CRC, implicating cohesin-mediated L1 expression in global genomic instability and gene dysregulation in cancer. : Rad21 holds the cohesin complex together as part of its role in chromosome partitioning and DNA repair. Xu et al. identify Rad21 as a key mediator of Apc gene heterozygous loss, the event initiating intestinal tumorigenesis. The subsequent activation of the Wnt pathway further induces Rad21, global gene dysregulation, chromosome instability, and pervasive retrotransposon activation.

This paper presents an analysis of the differential infrared thermography (DIT) technique, a contactless method of measuring the unsteady movement of the boundary layer transition position on an unprepared surface. DIT has been shown to measure boundary layer transition positions which correlate well with those from other measurement methods. In this paper unsteady aerodynamics from a 2D URANS solution are used and the resulting wall temperatures computed. It is shown that the peak of the temperature difference signal correlates well with the boundary layer transition position, but that the start and end of boundary layer transition cannot be extracted. A small systematic time-lag cannot be reduced by using different surface materials, but the signal strength can be improved by reducing the heat capacity and heat transfer of the surface layer, for example by using a thin plastic coating. Reducing the image time separation used to produce the difference images reduces the time-lag and also the signal level, thus the optimum is when the signal to noise ratio is at the minimum which can be evaluated.

A new approach on decreasing the optical shadowing of the solar cell grid fingers is presented. The approach relies on a local change of the optical properties in the bulk of the photovoltaic module encapsulation material ethylene vinyl acetate (EVA). In particular, scattering and diffractive optical elements are locally generated within the volume of cross-linked EVA encapsulation material by applying a femtosecond-laser-writing process. When these optical elements are located above the metal grid fingers, the optical shadowing of these grid fingers can be decreased. In an experimental proof of concept, the optical performance of this approach is demonstrated. The best results obtained so far indicate a decrease in optical shadowing by 17%. The material characteristics of the volume optics were investigated by applying confocal Raman microscopic characterisation, which indicates that the EVA material partially degraded upon the impact of the laser beam and is partly carbonised. Supplementary optical simulations show that the light deflection is caused by diffraction. However, parasitic absorption substantially deteriorates the optical performance of the deflective volume optics. Copyright © 2014 John Wiley & Sons, Ltd.

Vibrational spectroscopy was found to be a suitable method for the determination of the degree of cross-linking of ethylene vinyl acetate (EVA) polymers. Spectral changes in the Raman spectra of EVA with increasing lamination time (which equals increasing degree of cross-linking) were mainly detected in the CH vibrational regions, namely, in the relative intensities of the characteristic CH3 and CH2 bands. These spectral regions were chosen for a chemometric evaluation where a calibration was performed with the Raman spectra of reference EVA samples and the results obtained from corresponding thermal analysis (differential scanning calorimetry) and Soxhlet extraction data. These datasets were subsequently used to non-destructively determine the progress of cross-linking in EVA foils, embedded in various mini-modules by Raman microscopy. Thus, we could show that Raman spectroscopy is a highly interesting method for quality control in the production of photovoltaic (PV) modules. However, this approach is valid only for a given grade of EVA, meaning a demand for a new calibration when changing the supplier or the type of EVA used. In addition, the applicability of infrared spectroscopy for the determination of the degree of cross-linking was tested. A good correlation of the decrease in intensity of the characteristic cross-linker infrared bands with increasing progress of the cross-linking was found, as determined by reference methods. However, this analytical method requires taking samples of the EVA foils and is, thus, unsuitable for the non-destructive determination of the degree of cross-linking of the EVA encapsulated within a PV module.

A total of 16 analytical methods, spanning from classical solvent extraction over different thermo-analytic and mechanical approaches to acoustic and optical spectroscopy, have been evaluated as to their ability to determine the crosslinking state of ethylene vinyl acetate (EVA), the prevailing encapsulant for photovoltaics applications. The key objective of this work was to create a systematic and comprehensive comparison, using a unified set of traceable test samples covering the full range of realistically occurring degrees of EVA crosslinking. A majority number of these tested methods proved fundamentally suitable for detecting changes in the polymer properties during crosslinking based on the effect e.g. its mechanical properties or its crystallinity. Interestingly, when investigated in detail, most of the methods showed mutually different dependencies on the lamination time, indicating a complex range of effects of the chemical crosslinking on the properties and behaviour of the material. Furthermore, Raman spectroscopy could be identified as a potential new method for measuring the degree of crosslinking in-line in the PV module manufacturing process, thus providing an interesting approach for improving process control in PV module processing.