1,720,960 research outputs found
Assessment of estimation methods of DNI resource in solar concentrating systems
No full textThe DNI (Direct Normal Irradiance) is the resource utilized by solar concentrators, in CSP and CPV applications. However, it is not often measured due to practical reasons, and is derived instead from measurements of global irradiance or satellite-based models. This paper describes a study of different estimation procedures for the assessment of the DNI, using experimental data with a time scale of 1 min, taken at two different latitudes in Italy. The analyzed approaches include measuring techniques and models. Accurate estimations of DNI are obtained as derived from measurements of global horizontal irradiance and diffuse horizontal irradiance if the offset in pyranometers are properly corrected and the zenith angle is not too high. The measured and calculated values of DNI are used to estimate the hourly, daily, monthly and seasonal irradiation. The results show that the different estimation methods can lead to quite different conclusions when comparing short-term and long-term solar radiation availability. © 2015 Elsevier Lt
DNI estimation procedures for the assessment of solar radiation availability in concentrating systems
No full textDNI (Direct Normal Irradiance) is the resource utilized by solar concentrators. Besides, the determination of DNI is needed in the models for the estimation of global irradiance on tilted planes, which is the input to flat-plate systems. This paper describes a study of different estimation procedures for the assessment of the DNI, using experimental data with a time scale of 1 min, taken at two different latitudes. The analyzed approaches include measuring techniques and models. The results show that the different estimation methods can lead to quite different conclusions when comparing the solar radiation availability in concentrating and flat-plate systems and this can affect the energy and economic evaluations. Based on the experimental analysis, indications for reducing the uncertainty in the estimation of DNI are discussed
Theoretical analysis of two novel hybrid thermoelectric-photovoltaic systems based on Cu2ZnSnS4 solar cells
No full textThe development and commercialization of Photovoltaic (PV) cells with good cost-efficiency trade-off not using critical raw materials (CRMs) is one of the strategies chosen by the European Community (EC) to address the Energy Roadmap 2050. In this context Cu2ZnSnS4 (CZTS) solar cells are attracting a major interest since they have the potential to combine low price with relatively high conversion efficiencies. Although a ≈9% lab scale efficiency has already been reported for CZTS this technology is still far from being competitive in terms of cost per peak-power (€/Wp) with other common materials. One possible near-future solution to increase the CZTS competiveness comes from thermoelectrics. Actually it has already been shown that Hybrid Thermoelectric-Photovoltaic Systems (HTEPVs) based on CIGS, another kesterite very similar to CZTS, can lead to a significant efficiency improvement. However it has been also clarified how the optimal hybridization strategy cannot come from the simple coupling of solar cells with commercial TEGs, but special layouts have to be implemented. Furthermore, since solar cell performances are well known to decrease with temperature, thermal decoupling strategies of the PV and TEG sections have to be taken. To address these issues, we developed a model for two different HTEPV solutions, both coupled with CZTS solar cells. In the first case we considered a Thermally-Coupled HTEPV device (TC-HTEPV) in which the TEG is placed underneath the solar cell and in thermal contact with it. The second system consists instead of an Optically-Coupled but thermally decoupled device (OC-HTEPV) in which part of the solar spectrum is focused by a non-imaging optical concentrator on the TEG hot side. For both solutions the model returns conversion efficiencies higher than that of the CZTS solar cell alone. Specifically, increases of ≈30% are predicted for both kind of systems considered. Copyright © 2017 American Scientific Publishers All rights reserved
Sviluppo e caratterizzazione di componenti solari per applicazioni di solar cooling
Get PDFNell’ambito dell’Accordo di Programma ENEA –MiSE, il presente documento contiene gli esiti delle attività teorico‐sperimentali condotte nel corso dell’annualità 2011‐2012 presso il Centro Ricerche ENEA di Trisaia, relativamente alla linea di attività riguardante lo Sviluppo e caratterizzazione di componenti solari per applicazioni di solar cooling, afferente al Progetto sull’utilizzo dell’energia elettrica e solare per la climatizzazione estiva. Le attività hanno riguardato: 1. lo sviluppo di un prototipo di concentratore solare compatto, basato su ottiche del tipo CPC che inizialmente è stato oggetto di uno studio modellistico sia ottico che termo‐fluidodinamico al fine di ottimizzare lo scambio termico e massimizzarne l’efficienza alle temperature di lavoro richieste. Successivamente si è proceduto all’implementazione del prototipo utilizzando i materiali e tecniche costruttive di tipo innovativo. Durante le varie fasi di realizzazione, il prototipo è stato sottoposto a diversi test al fine di verificarne le caratteristiche termomeccaniche. 2. la progettazione e realizzazione di un simulatore solare per l’esecuzione di prove indoor su collettori solari di diversa tipologia, al fine di analizzarne le performance energetiche, in vista anche della verifica di modelli matematici per la cui validazione sono richieste condizioni controllate. 3. la sperimentazione e qualificazione di componenti e sistemi allo stato pre‐industriale o di prototipo per applicazioni solari a bassa e media temperatura. In quest’ambito sono stati analizzati e caratterizzati gli effetti geometrici che influenzano il comportamento termico sia di concentratori parabolici lineari sia di sistemi a specchi lineari di Fresnel. Inoltre sono state condotte sperimentazioni su sistemi ibridi a concentrazione del tipo Dish/Stirling, ottenendo risultati interessanti dal punto di vista delle performance elettriche e termiche
Energy performance assessment of solar-assisted desiccant cooling system
No full textSolar systems have the main purpose of replacing fossil fuel based systems so as to attain a primary energy saving. In this context, the recourse to solar-assisted air conditioning systems in buildings represents a suitable choice not only to reduce the final energy consumptions but also to enlarge the utilization field of solar thermal energy. On the other hand, different technical solutions can be profitably employed. Among these, desiccant cooling systems (DEC) represent an interesting option to be investigated. Aim of this work is to assess the potential of solar-assisted air conditioning systems based on a desiccant cooling cycle which regenerating heat is supplied by low temperature solar thermal collectors.
In the present study a comparative analysis, based on an energy saving approach by comparison with an electrically driven vapour compression heat pump (assumed as reference convectional cooling and heating machine), has been carried out. In order to assess the energy performance of the solar-assisted desiccant cooling system, different plant configurations have been investigated by means of suitable TRNSYS simulation models. The analysis has been performed for a typical residential building (a terraced house) located in Palermo, whose heating and cooling loads have been estimated by means of EnergyPlus simulation program and used in TRNSYS as input file. Concerning DEC system, both recirculation and ventilation modes have been examined. The regeneration heat has been supplied by a water heater solar system powered by evacuated tubular collectors and assisted by an in line air-heater. An apposite control strategy, based on both the control of inlet humidity and the following of regeneration temperature, has been implemented. For all the considered configurations, thermal COP (evaluated as the ratio between the cooling capacity and the regeneration heat), consumed primary energy and solar fractions (evaluated on monthly and annual basis) have been calculated.
From the results obtained, a techno-economic comparison, relevant to other thermally driven air conditioning systems (single and double effect absorption chillers using water/LiBr, advanced cycles using ammonia/water and adsorption chillers), has been carried out. This in order to assess the energy and the cost effectiveness of DEC systems compared with other solar-assisted technologies.
The obtained results show the capacity of these systems to reduce significantly the primary energy consumption. On the other hand, some open questions remain: the cost-effectiveness compared to reference conventional heating/cooling systems and the assessment of how the electrical energy consumption (due to high air flow rates and large pressure drops) could affects (affect) the overall primary energy saving
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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