1,720,988 research outputs found
Integration of photovoltaic and concentrated solar thermal technologies for H2 production by the hybrid sulfur cycle
No full textIt is widely agreed that hydrogen used as energy carrier and/or storage media may significantly contribute in the reduction of emissions, especially if produced by renewable energy sources. The Hybrid Sulfur (HyS) cycle is considered as one of the most promising processes to produce hydrogen through the water-splitting process. The FP7 project SOL2HY2 (Solar to Hydrogen Hybrid Cycles) investigates innovative material and process solutions for the use of solar heat and power in the HyS process. A significant part of the SOL2HY2 project is devoted to the analysis and optimization of the integration of the solar and chemical (hydrogen production) plants. In this context, this work investigates the possibility to integrate different solar technologies, namely photovoltaic, solar central receiver and solar troughs, to optimize their use in the HyS cycle for a green hydrogen production, both in the open and closed process configurations. The analysis carried out accounts for different combinations of geographical location and plant sizing criteria. The use of a sulfur burner, which can serve both as thermal backup and SO2 source for the open cycle, is also considered. © 2017 Author(s)
Thermal characterization of a cavity receiver for hydrogen production by thermochemical cycles operating at moderate temperatures
No full textThe manganese-ferrite thermochemical cycle developed by ENEA for hydrogen production, whose maximum temperature level lays in the range 750-800. °C, has a high potential for coupling with the solar source using conventional structural materials. As a first step for the on sun feasibility validation of the cycle, an experimental survey of the thermal performance of a receiver-reactor designed by ENEA, to be powered by a solar furnace (1. kW), has been carried out in the absence of a reaction. The temperature distribution over the reactor chamber as a function of solar irradiation has been measured and the thermal inertia of the system has been evaluated. The experimental results confirm that the reactor temperature and inertia are compatible with the manganese-ferrite cycle and other cycles operating at moderate temperatures. In order to set the basis for the evaluation of this and other similar prototypes, a finite element model (FEM) has been developed to describe the thermofluidodynamic behavior of the reactor. Good agreement between calculated and experimental data has been obtained; therefore this model will be improved and extended to describe both the hydrogen and oxygen releasing reactions of the manganese-ferrite cycle, with the aim of optimizing the reactor design. © 2013 Elsevier Ltd
Hydrogen production by the solar-powered hybrid sulfur process: Analysis of the integration of the CSP and chemical plants in selected scenarios
No full textThe Hybrid Sulfur (HyS) is a water splitting process for hydrogen production powered with high temperature nuclear heat and electric power; among the numerous thermo-chemical and thermo-electro-chemical cycles proposed in the literature, such cycle is considered to have a particularly high potential also if powered by renewable energy. SOL2HY2 (Solar to Hydrogen Hybrid Cycles) is a 3 year research project, co-funded by the Fuel Cells and Hydrogen Joint Undertaking (FCH JU). A significant part of the project activities are devoted to the analysis and optimization of the integration of the solar power plant with the chemical, hydrogen production plant. This work reports a part of the results obtained in such research activity. The analysis presented in this work builds on previous process simulations used to determine the energy requirements of the hydrogen production plant in terms of electric power, medium (550°C) temperature heat. For the supply of medium temperature (MT) heat, a parabolic trough CSP plant using molten salts as heat transfer and storage medium is considered. A central receiver CSP (Concentrated Solar Power) plant is considered to provide high temperature (HT) heat, which is only needed for sulfuric acid decomposition. Finally, electric power is provided by a power block included in the MT solar plant and/or drawn from the grid, depending on the scenario considered. In particular, the analysis presented here focuses on the medium temperature CSP plant, possibly combined with a power block. Different scenarios were analysed by considering plants with different combinations of geographical location and sizing criteria. © 2016 Author(s)
Heat Supply to Industrial Processes via Molten Salt Solar Concentrators
Full text linkAbout one-third of world energy production is destined to the industrial sector, with process heat accounting for about 70% of this demand; almost half of this quota is required by endothermic processes operating at temperatures above 400 °C. Concentrated solar thermal technology, thanks to cost-effective high-temperature thermal energy storage solutions, can respond to the renewable thermal energy needs of the industrial sector, thus supporting the decarbonization of hard-to-abate processes. Particularly, parabolic trough technology using binary molten salts as heat transfer fluid and storage medium, operating up to 550 °C, could potentially supply a large part of the high-temperature process heat required by the industry. In this work, four industrial processes, representative of the Italian industrial context, that are well suited for integration with molten salt concentrators are presented and discussed, conceiving for each considered process a specific coupling solution with the solar plant, sizing the solar field and the thermal storage unit, and computing the cost of the process heat and its variation with the storage capacity. Considering cost data from the literature associated with the pre-COVID-19 era, an LCOH comprising the range 5–10 c€/kWhth was obtained for all the cases studied, while taking into account more updated cost data, the calculated LCOH varies from 7 to 13 c€/kWhth
High temperature solar linear receiver enclosed in a reflecting elliptic cavity
No full textA linear receiver able to achieve temperatures up to 800 °C is presented. The high-temperature resistance is achieved by avoiding critical aspects (vacuum, glass-metal joints, surface films) that limit the temperature in usual receivers; the thermal insulation is obtained by enclosing the receiver tube in an elliptic reflecting cavity. The tube is placed near a focus of the cavity, and the primary collector concentrates the radiation on the other focus, where the cavity has a small opening: the ellipse reflects the radiation toward the tube and largely contains the reflected radiation and thermal emission, thus acting both as a secondary reflector and as a cavity receiver. Optical and thermal simulations show that temperatures up to 800 °C can be achieved, with optical efficiency above 70% and thermal efficiency in the range 45-85% for temperatures in the range 500-800 °C; the local overall efficiency ranges from about 40% to 66%, depending on the receiver tube emissivity and fluid temperature. In this way, the field of applicability of the linear collector technology can be significantly extended to include a vast amount of processes such as thermochemical cycles for hydrogen production, and solar fuel production processes, which require temperatures above 700 °C
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Spectrally selective solar coating based on W-AlN cermet fabricated by reactive sputtering processes at high deposition rate
No full textThe low cost fabrication of thermally stable solar coatings having high photo-thermal performance through high deposition rate processes represents one of the most demanding challenges in linear focusing Concentrated Solar Power (CSP) technology. Since 2005, ENEA has been developing and patenting solar coatings suitable for medium and high temperature applications based on the technology of double nitride cermet. The absorber layer of these coatings is characterized by a graded multilayer cermet of tungsten nitride and aluminium nitride (WN-AlN), while the ceramics of the antireflection filter are constituted by aluminium nitride (AlN) and silica (SiO2). The technology employed to deposit the ceramic component of all cermet materials, as well as of the antireflection filter, is reactive magnetron sputtering in poisoned mode, which does not allow obtaining the best trade-off between deposition rate and energy consumption. In order to improve the economic feasibility of linear focusing CSP solar plant, a cost-effective process was developed in the present work to produce spectral selective coatings for solar receiver tubes. To achieve this objective, the reactive magnetron sputtering technology in transition mode was applied to deposit all ceramic constituents of solar coatings. In detail, the antireflection ceramics were deposited through "dual magnetron"reactive sputtering in transition mode with Medium Frequency (MF) supply and using a Plasma Emission Monitoring (PEM) control system to maintain unchanged the target conditions during the process. It was found that, when using this technology in place of that in poisoned mode, the deposition rate improves by 1.6 and 2.3 times for AlN and SiO2, respectively. Regarding the graded multilayer cermet, while the ceramic component was deposited by "dual magnetron"reactive sputtering in transition mode with MF supply, the metallic component was deposited by "standard magnetron"sputtering with Direct Current (DC) supply. The process control through PEM system was simplified in this case by introducing N2 only from the gas-ring around the Al targets. Since in this configuration the reactive gas flow was not sufficient to promote the formation of WN as metallic component inside the cermet, the double nitride cermet WN-AlN was replaced by W-AlN. A fast procedure was developed to grow the W-AlN multilayer cermet by employing only one hysteresis curve to control the deposition process and grow the cermet layers in sequence. Specifically, this method presents the advantage that it is not necessary to stop and re-start PEM control, power supply and gas injection between the deposition of consecutive cermet layers. The fast procedure was applied to fabricate the absorber layer of the solar coating allowing to obtain a 44% reduction in the energy consumption by replacing WN with W as a metallic component of the multilayer cermet. The coating was subjected to a stability study at high temperature including the estimation of thermal degradation of the photo-thermal parameters after heat treatments under vacuum (2·10-2 Pa) for a total duration of 33 days at the temperature of 620 °C. The results revealed that no appreciable modification occurred in terms of solar absorptance (αs), while a very small increment of thermal emittance (εth) was evaluated at 400°C, thus demonstrating the excellent thermal stability of the produced coating
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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