Degradation of photovoltaic backsheets: Comparison of the aging induced changes on module and component level

In reliability testing of components for PV modules an always remaining question is about material (in)compatibilities and synergistic effects and thus, how results of singly tested materials correlate with materials aged within PV modules. Testing of single materials would simplify sample preparation, reduce costs and offer more testing options. Therefore the main objective of this study was to compare the aging behavior of single backsheets with that of backsheets incorporated within PV modules. Four different types of backsheets were chosen, all of them comprising of polyethylene terephthalate (PET) core layers, but differing outer protection layers. Test modules using identical components, varying only in the type of backsheet used were produced and damp heat aged (85°C/85% RH ≤2000 h). The results revealed no influence of the PV module lamination on the thermal characteristics of the polymeric backsheets. Even after DH aging, differences between single and module laminated backsheets were negligible. Degradation effects of PET could be detected for all aged sheets by thermal analysis and were confirmed by tensile tests and rheological measurements. Thus, it can be stated that testing of single PET based backsheets under DH aging conditions is a practicable way to investigate the applicability of a new backsheet. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42093.     

Effect of inter-plies on the short beam shear delamination of steel/composite hybrid laminates

Interlaminar shear test methods (ILS) were implemented to characterize the delamination behavior of asymmetric steel/carbon fiber reinforced plastic (CFRP) hybrids. To improve the delamination behavior thermoplastic inter-plies were inserted between CFRP and steel. Supported by optical strain measurement the maximum shear stress (τ_MAX), the shear stress at interfacial delamination (τ_IF) and the shear stress at large-scale CFRP ply delamination τ_D were evaluated. The significant effect of inter-plies on the adhesion was best reflected by the shear stress value at interfacial delamination. Finite element analysis of the actual shear stress distribution in an asymmetric hybrid sample without inter-ply revealed that the calculated shear strength is just slightly overestimated compared to the standardized evaluation procedure.     

A theoretical analysis of procurement auctions for tertiary control in Germany

As far as energy policy is concerned, the design of the regulatory framework for energy transmission and distribution is a key issue. Consequently, also the embodiment of balancing power markets drives mainly the effectiveness of political implications for the energy sector. Initially, tertiary control in Germany was solely offered by transmission system operators of the respective power control areas and their associated power plant. The recast of the Energy Industry Act of 2005 led in last consequence to a common procurement auction for the supply of tertiary control, which starts on December 1, 2006. Admittedly, the reform has fallen short of expectations so far, first concerning the intensification of market entry of tertiary control providers as well as the desired decline of the price level. Hence, this article examines the effects of the changeover on observable demand charges. In order to identify attributes of the common procurement auction for tertiary control hampering market entry of providers, giving stimuli to collusion and strategic behavior, reducing intensity of competition and encouraging an upswing of prices, we analyze the design under an auction theoretical approach and deduce empirically whether structural components of the auction design have to be touched up again.     

Cobalticenium-Bridged polybenzazoles. Part II: High-temperature. Solution polymerization in ethylated polyphosphoric acid

The polycondensation of 1,1′-diearboxycobalticenium hexafluorophosphate with 3,3′-diaminobenzidine in ethylated poly phosphoric acid at 100-240°C furnishes linear, soluble polymeric intermediates for the most part composed of cobalticenium-1,1′-diyl and bibenzimidazoline-2,2′-diyl units alternating along the chain. Heating of the primary products in the solid state at 300°C results in aromatization, giving polyheterocyclics essentially composed of alternating cobalticenium-1,1′-diyl and bibenzimidazole-2,2′-diyl units. The analogous reaction of the cobalticenium salt with 3,3′dimercaptobenzidine produces primary polymers containing benzothiazoline in lieu of benzimidazoline ring systems, which, by a heat treatment as before, convert to the corresponding polymeric benzothiazoles. The primary condensation products of both reaction types are of low molecular mass (η_inh, 5-13 ml/g) vlien prepared at temperatures not exceeding 150°C. The degree of polymerization increases (η_inh, 20-60 ml/g) at temperatures in the 200-250°C range; however, Lewis acid-induced cobalt-ring bond cleavage proceeds as a significant side reaction under these conditions, leading to random chain scission and alteration of the polymer structure by alicvclic hydrocarbon groups. In addition, the benzimidazole polymers are to a variable extent contaminated with phosphate groups stemming from the medium. These structural defects, paired with distinct reactivity of the PF₆^- anion at higher temperatures, result in a thermogravimetric analysis performance not quite equal to that of common phenylene-bridged Polybinzazoles.     

An asynchronously controlled EEG-based virtual keyboard: improvement of the spelling rate

An improvement of the information transfer rate of brain-computer communication is necessary for the creation of more powerful and convenient applications. This paper presents an asynchronously controlled three-class brain-computer interface-based spelling device [virtual keyboard (VK)], operated by spontaneous electroencephalogram and modulated by motor imagery. Of the first results of three able-bodied subjects operating the VK, two were successful, showing an improvement of the spelling rate sigma, the number of correctly spelled letters/min, up to sigma = 3.38 (average sigma = 1.99).     

Flanker effects with faces may depend on perceptual as well as emotional differences.

Do threatening or negative faces capture attention? The authors argue that evidence from visual search, spatial cuing, and flanker tasks is equivocal and that perceptual differences may account for effects attributed to emotional categories. Empirically, the authors examine the flanker task. Although they replicate previous results in which a positive face flanked by negative faces suffers more interference than a negative face flanked by positive faces, further results indicate that face perception is not necessary for the flanker-effect asymmetry and that the asymmetry also occurs with nonemotional stimuli. The authors conclude that the flanker-effect asymmetry with affective faces cannot be unambiguously attributed to emotional differences and may well be due to purely perceptual differences between the stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Search asymmetries with real faces: Testing the anger-superiority effect.

The anger-superiority hypothesis states that angry faces are detected more efficiently than friendly faces. Previously research used schematized stimuli, which minimizes perceptual confounds, but violates ecological validity. The authors argue that a confounding of appearance and meaning is unavoidable and even unproblematic if real faces are presented. Four experiments tested carefully controlled photos in a search-asymmetry design. Experiments 1 and 2 revealed more efficient detection of an angry face among happy faces than vice versa. Experiment 3 indicated that the advantage was due to the mouth, but not to the eyes, and Experiment 4, using upright and inverted thatcherized faces, suggests a perceptual basis. The results are in line with a sensory-bias hypothesis that facial expressions evolved to exploit extant capabilities of the visual system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimization and Biomass Utilization in Heavy Metal Recycling

Environmental legislation, limited resources as well as high metal prices force the metallurgical industry more and more to make use of secondary materials. For this, also residues from metal production are nowadays considered as a possible resource. Due to their often complex structure and the presence of a multi-metal-system, efficient recycling of such materials is not easy to realize and suffers from various problems. The Christian Doppler Laboratory for Optimization and Biomass Utilization in Heavy Metal Recycling together with its partner companies Befesa R&D, voestalpine Stahl Linz, RHI, and Aurubis investigate alternative strategies and optimization possibilities for the considered residues. The achievements of three years’ activity in the major fields of the CDL, characterization of the complex input materials, upgrade of the product quality of recycling processes, utilization of biomass in the form of charcoal for use as a reducing agent and simultaneous recovery of valuable metals are described in the paper.     

Correlation of spatially resolved photoluminescence and viscoelastic mechanical properties of encapsulating EVA in differently aged PV modules

The photoluminescence of ethylene vinyl acetate (EVA) in aged photovoltaic modules shows specific spatial patterns on the scale of the cells in the module that depend on the aging conditions. It is the aim of this work to investigate the correlation of these photoluminescence patterns to the viscoelastic mechanical properties of the encapsulating EVA. For this, the degradation under various conditions of two specimen sets of polycrystalline silicon photovoltaic mini‐modules, comprising EVA as encapsulating polymer, is investigated using spatially resolved, ultraviolet‐excited photoluminescence. Samples of the encapsulation EVA are systematically extracted from the modules for spatially resolved dynamic mechanical characterization. A correlation between the spatial distribution of the photoluminescence intensity and the values of storage modulus and loss factor of the EVA is found. An increase in the values for storage modulus and a decrease of the loss factor of the EVA from the edge of the cell towards the center are observed for all samples. We conclude that diffusion‐limited oxidation must be considered for aging studies of the encapsulation EVA and that photoluminescence detection can reveal the scale on which such diffusion processes occur. Copyright © 2016 John Wiley & Sons, Ltd.