1,720,981 research outputs found
Results of the Fifth International Spectroradiometer Comparison for Improved Solar Spectral Irradiance Measurements and Related Impact on Reference Solar Cell Calibration
No full textThis paper reports on the results of the fifth spectral irradiance measurement intercomparison and the impact these results have on the spread of spectral mismatch calculations in the outdoor characterization of reference solar cell and photovoltaic (PV) devices. Ten laboratories and commercial partners with their own instruments were involved in the comparison. Solar spectral irradiance in clear sky condition was measured with both fast fixed and slow rotating grating spectroradiometers. This paper describes the intercomparison campaign, describes different statistical analysis used on acquired data, reports on the results, and analyzes the impact these results would have on the primary calibration of a c-Si PV reference cell under natural sunlight
Numerical characterization of a highly concentrated solar radiation sensor based on an inverse method
No full textThis paper focuses on the numerical characterization of a new sensor for the measurement of highly concentrated radiative heat fluxes, based on an inverse heat transfer method. The sensor will be coupled to the solar furnace that is being installed at the ENEA Portici Research Center. The highly concentrated radiative heat flux incident on the target surface of the sensor is estimated by implementing the inverse heat transfer method based on the Levenberg-Marquardt algorithm, which permits to compute the radiative boundary condition on the exposed surface of the target by measuring the temperature of its hidden bottom surface. Numerical simulations have been carried out to evaluate the sensor sensitivity to the following parameters: the emissivity of the target surface of the sensor; the synchronization error in the temperature recordings; the uncertainty in temperature measurements; the convection heat transfer coefficient; the misalignment between the axis of the target and the axis of the concentrated solar spot; the uncertainty about the values of the thermo-physical properties of the sensor components materials
Intercomparison campaign of spectroradiometers for a correct estimation of solar spectral irradiance: results and potential impact on photovoltaic devices calibration
No full textThis paper describes the results of an intercomparison of spectroradiometers for global and direct normal incidence irradiance in the visible and near infrared spectral regions together with an assessment of the impact these results may have on the estimation of the short-circuit current (Isc) calibration of photovoltaic devices and on the spectral mismatch calculation. The intercomparison was conducted in the framework of the European project Apollon with the additional participation of external partners from the Italian project for the long-term monitoring of solar radiation for photovoltaics. Six institutions and six spectroradiometer systems, representing different technologies and manufacturers, were involved. Prior to the imtercomparison, all participating partners calibrated their own instrument(s) according to their usual procedures in order to verify the entire measuring and traceability chain. The difference in measured spectra shape and amplitude showed to have an impact on Isc calculation of less than 3% and less than 6% for single-junction and multi-junction devices, respectively. When only the shape of the spectra is considered, the specta mismatch ranges from 1.7% to 4.7% depending on the spectral response of the device
A procedure for assessing the reliability of short circuited concentration photovoltaic systems in outdoor degradation conditions
No full textA procedure for assessing the reliability functions of photovoltaic concentration (CPV) systems, subjected to outdoor degradation, will be described in this work. The evaluation of the concentrator cells failure rate, the understanding of the origin of these degradation modes and how they affect the performances of concentration cells is an essential step to improve their reliability and to accelerate their competitiveness. The reliability evaluation methodology introduced here, as the cells are deployed outdoors and then are subjected to the actual sources of stress (e.g.: ambient temperature, solar concentrated irradiance, cells working temperature and the variations of these parameters over days and seasons), will furnish values of failure rates very close to the true ones
Characterization of high-efficiency c-Si CPV cells
No full textConcentrating photovoltaics (CPV) represent an emerging market at its early stage for terrestrial applications with large growth expectation and considerable research activity on new cell production has been conducting recently. In response to a fast growing demand for traceable and independent measurements on CPV cells and systems the European Solar Test Installation (ESTI) has started a research program on indoor/outdoor devices characterization. This paper focuses on two essential components of device calibration. Calibration requires traceable calibrated reference devices: for this purpose reference c-Si cells equipped with neutral density filters of various optical densities have been used at ESTI for checking device linearity at different concentration ratios. Also essential is the implementation of common procedures and intercomparison of test results at different test laboratories. Procedures and experimental setups for concentrating c-Si cell characterization at both ESTI and at the UTTP FOTO Laboratory of ENEA are described and results of an intercomparison are presented and discussed. Electrical performance measurements have been performed at high intensities on three different setups: a recently developed 1500x pulsed solar simulator at ESTI and two modified solar simulators capable of achieving up to 250x concentration at ENEA. Reported results show agreement within measurement uncertainties of the electrical parameters
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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