The Experts below are selected from a list of 192 Experts worldwide ranked by ideXlab platform
Ramon Pujol-nadal - One of the best experts on this subject based on the ideXlab platform.
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On-site optical characterization of large-scale solar collectors through ray-tracing optimization
Applied Energy, 2020Co-Authors: Julian David Hertel, Vincent Canals, Ramon Pujol-nadalAbstract:Abstract In order to increase the trust and willingness to invest in concentrating solar collectors, an accurate labeling and certification process is of utmost importance. Today’s collector testing standards specify methods for assessing the thermal performance of most types of fluid heating solar collectors. However, they do not provide an applicable testing procedure for obtaining the incidence angle Modifier of large-scale line-focusing collectors. Such collectors need to be tested directly in the field, where optical characterization by conventional methods, such as factorization, fails. This study presents a new approach to obtain the incidence angle Modifier by fitting ray-tracing curves to the measured optical efficiency data set. The new method has been tested on a fixed mirror solar concentrator with a mobile focus. Prior to this study, 49 experimental data points have been obtained for the optical efficiency after measuring for four testing days according to the ISO 9806 rules. These experimental data points served as a basis for the fitting procedure to validate the ray-tracing model. Stable optimized solutions of the collector’s optical parameters have been determined within a reasonable computation time scale. From a comparison of the optimized solution to a simplified ray-tracing simulation, it was seen that the weighted root-mean-square error was improved by 27.7%. In conclusion, the proposed procedure overcomes practical hurdles and has many advantages over conventional methods.
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Influence of thermal losses on the incidence angle Modifier factorization approach
Solar Energy, 2016Co-Authors: Julian David Hertel, Víctor Martínez-moll, Ramon Pujol-nadalAbstract:Abstract Solar thermal applications for industries must be designed to operate at high temperature levels; however, the thermal dependency of the accuracy of the incidence angle Modifier factorization has not been sufficiently analyzed. In this study, the annually delivered energy based on both factorized and non-factorized incidence angle Modifier values were compared with each other. The integration was conducted for a typical meteorological year in Seville and Stockholm. Four collector types were considered: evacuated tube collector, MaReCo collector, Fresnel collector, and CCStaR collector. Thermal process parameters were shown to have an influence on the error made by the factorization approach; however, within the economically viable temperature range of an industrial heat application, this influence is not significant.
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Optical losses due to tracking error estimation for a low concentrating solar collector
Energy Conversion and Management, 2015Co-Authors: Fabienne Sallaberry, Alberto García De Jalón, José-luis Torres, Ramon Pujol-nadalAbstract:Abstract The determination of the accuracy of a solar tracker used in domestic hot water solar collectors is not yet standardized. However, while using optical concentration devices, it is important to use a solar tracker with adequate precision with regard to the specific optical concentration factor. Otherwise, the concentrator would sustain high optical losses due to the inadequate focusing of the solar radiation onto its receiver, despite having a good quality. This study is focused on the estimation of long-term optical losses due to the tracking error of a low-temperature collector using low-concentration optics. For this purpose, a testing procedure for the incidence angle Modifier on the tracking plane is proposed to determinate the acceptance angle of its concentrator even with different longitudinal incidence angles along the focal line plane. Then, the impact of maximum tracking error angle upon the optical efficiency has been determined. Finally, the calculation of the long-term optical error due to the tracking errors, using the design angular tracking error declared by the manufacturer, is carried out. The maximum tracking error calculated for this collector imply an optical loss of about 8.5%, which is high, but the average long-term optical loss calculated for one year was about 1%, which is reasonable for such collectors used for domestic hot water.
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Direct tracking error characterization on a single-axis solar tracker
Energy Conversion and Management, 2015Co-Authors: Fabienne Sallaberry, Ramon Pujol-nadal, Michele Larcher, Mercedes Hannelore Rittmann-frankAbstract:The solar trackers are devices used to orientate solar concentrating systems in order to increase the focusing of the solar radiation on a receiver. A solar concentrator with a medium or high concentration ratio needs to be orientated correctly by an accurate solar tracking mechanism to avoid losing the sunrays out from the receiver. Hence, to obtain an appropriate operation, it is important to know the accuracy of a solar tracker in regard to the required precision of the concentrator in order to maximize the collector optical efficiency. A procedure for the characterization of the accuracy of a solar tracker is presented for a single-axis solar tracker. More precisely, this study focuses on the estimation of the positioning angle error of a parabolic trough collector using a direct procedure. A testing procedure, adapted from the International standard IEC 62817 for photovoltaic trackers, was defined. The results show that the angular tracking error was within ±0.4° for this tracker. The optical losses due to the tracking were calculated using the longitudinal incidence angle Modifier obtained by ray-tracing simulation. The acceptance angles for various transversal angles were analyzed, and the average optical loss, due to the tracking, was 0.317% during the whole testing campaign. The procedure presented in this work showed that the tracker precision was adequate for the requirements of the analyzed optical system.
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Estimation of the influence of different incidence angle Modifier models on the biaxial factorization approach
Energy Conversion and Management, 2015Co-Authors: Julian David Hertel, Víctor Martínez-moll, Ramon Pujol-nadalAbstract:To minimize the experimental effort of assessing biaxial incidence angle characteristics of solar collectors with complex geometries, current testing standards (EN 12975-2, ASHRAE 93, ISO 9806:2013) recommend the factorization method proposed by McIntire (1982). Due to a lack of consensus, researchers in the low and high temperature fields of solar thermal have applied this model in very different ways, either referring to different radiation references (beam radiation on tilted surface vs. direct normal irradiance) or angle projections (θT-θL-domain vs. θT-θi-domain). In this study, the influence of each approach on the factorization error is estimated. Four different collector geometries were considered: compound parabolic collector, maximum reflector collector, linear Fresnel reflector, and fixed-mirror collector (Concentrating Collector with Stationary Reflector, CCStaR V2). The 3D incidence angle Modifier surface of each collector was calculated with a sophisticated in-house ray tracing tool and compared with the incidence angle Modifier surface constructed by various factorization models. The error was defined as difference between direct normal irradiance weighted annual integration of ray tracing and factorized incidence angle Modifier, given the collector’s location and orientation. This allows the deviations to be represented more intuitively by plotting the relative error over latitude. Factorization in the (θT,θi)-domain was shown to constantly yield accurate results even in the case of static collectors.
Fabienne Sallaberry - One of the best experts on this subject based on the ideXlab platform.
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Optical losses due to tracking error estimation for a low concentrating solar collector
Energy Conversion and Management, 2015Co-Authors: Fabienne Sallaberry, Alberto García De Jalón, José-luis Torres, Ramon Pujol-nadalAbstract:Abstract The determination of the accuracy of a solar tracker used in domestic hot water solar collectors is not yet standardized. However, while using optical concentration devices, it is important to use a solar tracker with adequate precision with regard to the specific optical concentration factor. Otherwise, the concentrator would sustain high optical losses due to the inadequate focusing of the solar radiation onto its receiver, despite having a good quality. This study is focused on the estimation of long-term optical losses due to the tracking error of a low-temperature collector using low-concentration optics. For this purpose, a testing procedure for the incidence angle Modifier on the tracking plane is proposed to determinate the acceptance angle of its concentrator even with different longitudinal incidence angles along the focal line plane. Then, the impact of maximum tracking error angle upon the optical efficiency has been determined. Finally, the calculation of the long-term optical error due to the tracking errors, using the design angular tracking error declared by the manufacturer, is carried out. The maximum tracking error calculated for this collector imply an optical loss of about 8.5%, which is high, but the average long-term optical loss calculated for one year was about 1%, which is reasonable for such collectors used for domestic hot water.
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Direct tracking error characterization on a single-axis solar tracker
Energy Conversion and Management, 2015Co-Authors: Fabienne Sallaberry, Ramon Pujol-nadal, Michele Larcher, Mercedes Hannelore Rittmann-frankAbstract:The solar trackers are devices used to orientate solar concentrating systems in order to increase the focusing of the solar radiation on a receiver. A solar concentrator with a medium or high concentration ratio needs to be orientated correctly by an accurate solar tracking mechanism to avoid losing the sunrays out from the receiver. Hence, to obtain an appropriate operation, it is important to know the accuracy of a solar tracker in regard to the required precision of the concentrator in order to maximize the collector optical efficiency. A procedure for the characterization of the accuracy of a solar tracker is presented for a single-axis solar tracker. More precisely, this study focuses on the estimation of the positioning angle error of a parabolic trough collector using a direct procedure. A testing procedure, adapted from the International standard IEC 62817 for photovoltaic trackers, was defined. The results show that the angular tracking error was within ±0.4° for this tracker. The optical losses due to the tracking were calculated using the longitudinal incidence angle Modifier obtained by ray-tracing simulation. The acceptance angles for various transversal angles were analyzed, and the average optical loss, due to the tracking, was 0.317% during the whole testing campaign. The procedure presented in this work showed that the tracker precision was adequate for the requirements of the analyzed optical system.
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Toward a standard testing methodology for solar thermal collectors with variable-geometry: The direct radiation incidence angle Modifier issue
Solar Energy, 2015Co-Authors: Fabienne Sallaberry, Alberto García De Jalón, Ramon Pujol-nadal, Víctor Martínez-mollAbstract:Abstract Solar thermal energy is able to provide a considerable fraction of the medium-temperature energy demand and should be more widely used in specific industrial sectors in 100–250 °C range. For energy collection within this temperature range, solar collector designs usually have optical concentration systems, and therefore, the optical behavior of these devices, especially Incidence Angle Modifier (IAM) term in the standard equations, is of paramount importance to the energy equation balance. In the last few decades various new designs have been developed specifically for industrial applications. At the end of 2013, the new revised version of International Standard ISO 9806 for solar thermal collector test methods was published for worldwide certification. This new Standard unifies all the former American, European and International Standards. However, some solar collector types still do not fit to the Standard testing methodology, in particular solar collectors with variable-geometry. This paper describes the points in International Standard ISO 9806 defined specifically for testing solar collectors with solar tracking and concentration, and present a theoretical model to specify the range of the incidence angles which should be tested on variable-geometry collectors to validate the IAM terms in the energy equation balance. Finally some issues are proposed to extend the scope of the current standards for testing collector designs with variable-geometry, in particular for medium-temperature applications.
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Characterization of optical losses due to tracking systems on a linear solar thermal concentrator
2015Co-Authors: Fabienne SallaberryAbstract:Solar thermal energy is able to provide a considerable fraction of the current and future energy demand in both, industrial and domestic sectors. This fact is reflected by the growing interest during the last decade in the design of new solar collectors in order to satisfy the increasing heating demands. For a wide range of operational temperatures, solar collectors can use optical concentration systems to optimize their efficiency. However, as optical concentration relies on beam radiation, it is necessary to use a solar tracker following the sun direction to maximize the amount of useful solar radiation received. The selection of the appropriate tracking systems matching the optical concentration factor is essential to achieve an optimal collector efficiency. Otherwise, the concentrator will experience high optical losses due to the inadequate focusing of the beam solar radiation onto its receiver, regardless of its quality. Even though the concentrating solar collectors are mentioned in the International Standards, the general testing methods cannot always be easily applied to unusual collector designs. Moreover, those testing methods consider the solar tracker as part of the solar collector so they do not characterize the impact of its precision on the overall efficiency. For those reasons, this thesis aims to contribute to the improvement of tracking errors estimation on single-axis solar trackers on a solar thermal collector, in particular linear through collectors. And therefore, it also aims to estimate the optical losses resulting from the tracker. This study consisted in the three following stages: First, a testing procedure was defined for solar trackers by adapting a testing method from an International Standard for photovoltaic double-axis trackers. The experiments were carried out using a simple procedure to determine the tracking elevation error. Second, the optical characterization of different concentrating solar collectors was performed through simulation and experiment. The optical behavior of the concentrator aimed to determine the dependency of its efficiency to the angular tracking error. For the simulation, a ray tracing program was employed, and for the experiment some tests of the collector optical efficiency were carried out. A good agreement was found between the simulation and the experimental results considering the measurement uncertainties. Third, the long-term optical losses due to the tracking error were estimated using the transversal incidence angle Modifier obtained previously by ray-tracing simulation or by experiment, and the tracking errors distribution estimation. The impact of the maximum tracking error angle upon the optical efficiency has been determined on different concentrating/tracking collector types. Finally, this thesis describes the points defined in the International Standards that should be improved in order to ascertain the influence of the tracking on the overall efficiency of concentrating/tracking solar collectors. Some points have been proposed for a future Standard testing procedure on trackers for solar thermal collectors.
Soteris A. Kalogirou - One of the best experts on this subject based on the ideXlab platform.
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Chapter 4 – Performance of Solar Collectors
Solar Energy Engineering, 2014Co-Authors: Soteris A. KalogirouAbstract:Chapter 4 deals with the methods to determine experimentally the performance of solar collectors. It outlines the various tests required to determine the thermal efficiency of solar collectors. Initially collector thermal efficiency measurement is presented and the effect of flow rate, collectors connected in series, and the standard requirements of the test are analyzed. Subsequently, the methods to determine the collector incidence angle Modifier for flat-plate and concentrating collectors are presented followed by the acceptance angle for concentrating collectors and the collector time constant. The dynamic test method is also presented followed by the efficiency parameter conversion and assessment of the uncertainty in solar collector testing. This is followed by the way the collector test results can be used for the preliminary collector selection. Subsequently, the quality test methods are presented followed by a review of European standards used for this purpose as well as details of the Solar Keymark certification scheme. Finally, the chapter describes the characteristics of data acquisition systems including portable data loggers.
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Performance of Solar Collectors
Solar Energy Engineering, 2009Co-Authors: Soteris A. KalogirouAbstract:Chapter 4 deals with the methods to determine experimentally the performance of solar collectors. It outlines the various tests required to determine the thermal efficiency of solar collectors. Initially collector thermal efficiency measurement is presented and the effect of flow rate, collectors connected in series, and the standard requirements of the test are analyzed. Subsequently, the methods to determine the collector incidence angle Modifier for flat-plate and concentrating collectors are presented followed by the acceptance angle for concentrating collectors and the collector time constant. The dynamic test method is also presented followed by the efficiency parameter conversion and assessment of the uncertainty in solar collector testing. This is followed by the way the collector test results can be used for the preliminary collector selection. Subsequently, the quality test methods are presented followed by a review of European standards used for this purpose as well as details of the Solar Keymark certification scheme. Finally, the chapter describes the characteristics of data acquisition systems including portable data loggers.
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prediction of flat plate collector performance parameters using artificial neural networks
Solar Energy, 2006Co-Authors: Soteris A. KalogirouAbstract:The objective of this work is to use Artificial Neural Networks (ANN) for the prediction of the performance parameters of flat-plate solar collectors. ANNs have been used in diverse applications and they have been shown to be particularly useful in system modeling and system identification. Six ANN models have been developed for the prediction of the standard performance collector equation coefficients, both at wind and no-wind conditions, the incidence angle Modifier coefficients at longitudinal and transverse directions, the collector time constant, the collector stagnation temperature and the collector heat capacity. Different networks were used due to the different nature of the input and output required in each case. The data used for the training, testing and validation of the networks were obtained from the LTS database. The results obtained when unknown data were presented to the networks are very satisfactory and indicate that the proposed method can successfully be used for the prediction of the performance parameters of flat-plate solar collectors. The advantages of this approach compared to the conventional testing methods are speed, simplicity, and the capacity of the network to learn from examples. This is done by embedding experiential knowledge in the network.
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Design and performance characteristics of a parabolic-trough solar-collector system
Applied Energy, 2003Co-Authors: Soteris A. Kalogirou, Stephen Lloyd, J. Ward, Polyvios EleftheriouAbstract:A comparison of the advantages and disadvantages of concentrating collectors against conventional flat-plate collectors are presented. This is followed by the design of a parabolic-trough solar-collector system, due consideration having been given to collector-aperture and rim-angle optimisation, together with the receiver-diameter selection. The collector characteristic curve gives a test slope of 0·441 and a test intercept equal to 0·642. The value of the test slope differs considerably from the initially predicted value: this is attributed to the heat losses from the receiver support brackets. Subsequent allowance for these losses is presented: this reduces the difference from 24·9% to 5·7%. Other tests are presented, including the determination of the collector's Incidence-Angle Modifier, time constant and acceptance angle.
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parabolic trough collector system for low temperature steam generation design and performance characteristics
Applied Energy, 1996Co-Authors: Soteris A. KalogirouAbstract:The collector's performance is tested according to Ashrae Standard 93, 19861. The collector's efficiency and Incidence-Angle Modifier are measured. The test slope and intercept are found to be 0.387 and 0.638 respectively. The collector's time constant is less than one minute and the collector's acceptance angle obtained from the test is ±0.5°, which in combination with the tracking mechanism maximum error (± 0.2°) implies that the system works continuously at almost maximum possible efficiency.
Julian David Hertel - One of the best experts on this subject based on the ideXlab platform.
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On-site optical characterization of large-scale solar collectors through ray-tracing optimization
Applied Energy, 2020Co-Authors: Julian David Hertel, Vincent Canals, Ramon Pujol-nadalAbstract:Abstract In order to increase the trust and willingness to invest in concentrating solar collectors, an accurate labeling and certification process is of utmost importance. Today’s collector testing standards specify methods for assessing the thermal performance of most types of fluid heating solar collectors. However, they do not provide an applicable testing procedure for obtaining the incidence angle Modifier of large-scale line-focusing collectors. Such collectors need to be tested directly in the field, where optical characterization by conventional methods, such as factorization, fails. This study presents a new approach to obtain the incidence angle Modifier by fitting ray-tracing curves to the measured optical efficiency data set. The new method has been tested on a fixed mirror solar concentrator with a mobile focus. Prior to this study, 49 experimental data points have been obtained for the optical efficiency after measuring for four testing days according to the ISO 9806 rules. These experimental data points served as a basis for the fitting procedure to validate the ray-tracing model. Stable optimized solutions of the collector’s optical parameters have been determined within a reasonable computation time scale. From a comparison of the optimized solution to a simplified ray-tracing simulation, it was seen that the weighted root-mean-square error was improved by 27.7%. In conclusion, the proposed procedure overcomes practical hurdles and has many advantages over conventional methods.
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Study on the general applicability of the collector efficiency model to solar process heat collectors
2019Co-Authors: Julian David HertelAbstract:espanolSegun varios estudios, la capacidad instalada de captadores solares termicos para proveer calor en procesos industriales se va a incrementar significativamente a lo largo de las proximas decadas. La gran variedad de disenos y temperaturas de este tipo de captadores hace complicada la evaluacion de sus rendimientos. Aunque el metdodo experimental quasi-dinamico ha sido disenado para la mayoria de modelos de captadores, sigue teniendo limitaciones o imprecisiones a la hora de evaluar captadores de mediana escala. Esta tesis analiza algunas de dichas limitaciones, centrandose principalmente en la evaluacion de la eficiencia optica. Para el analisis optico en esta tesis se ha desarrollado un algoritmo avanzado de raytracing. El algoritmo ha servido para realizar un analisis de sensibilidad de un captador Fresnel, para conseguir con ello un mayor conocimiento de los parametros mas influyentes en las simulaciones ray-tracing. Se ha llegado a dos conclusiones: En primer lugar, simulaciones espectrales no son relevantes para aplicaciones solares termicas, a no ser que la dispersion del espejo dependa significativamente de la longitud de onda. En segundo lugar, es imprescindible especificar la dependencia del angulo de incidencia de los materiales opticos para generar resultados precisos. En el caso de captadores concentradores biaxiales, se aplica el modelo de factorizacion del ‘incidence angle Modifier’. Por defecto, este modelo introduce errores factorizando funciones que no son factorizables. Se ha caracterizado el error para cuatro geometrias de captadores diferentes comparando el modelo de factorizacion con las simulaciones ray-tracing. Los resultados han sido presentados como funcion de la latitud geografica. La factorizacion en el espacio ? -? ha demostrado los mejores resultados para casi todos los casos. Cuatro geometrias diferentes fueron sometidas a simulaciones de ray-tracing para analizar la dependencia termica del mismo error de factorizacion. Se ha demostrado que a medida que aumenta la temperatura del proceso, aumenta tambien el error relativo de factorizacion, sin embargo, dentro del rango economicamente viable de temperaturas, el error se mantiene constante. Esto se debe a que a medida se incrementa la temperatura, el captador deja de operar primero en los momentos de angulos mas desfavorables para la factorizacion. catalaSegons diversos estudis, la capacitat instal·lada de captadors solars termics pel subministrament de calor en processos industrials s’incrementara significativament en els propers anys. La gran diversitat de dissenys i temperatures de treball d’aquest tipus de captador fa dificil l’avaluacio dels seus rendiments. Encara que el metode experimental quasi dinamic s’ha desenvolupat per la major part de models de captador, segueix tenint limitacions o imprecisions a l’hora d’avaluar captadors especifics per calor de proces. Aquesta tesi analitza algunes d’aquestes limitacions, centrant-se principalment en l’avaluacio de l’eficiencia optica. Per l’analisi optica, en aquesta tesi s’ha desenvolupat un algoritme avancat de raytracing. L’algoritme ha servit per realitzar una analisi de sensibilitat d’un captador Fresnel, que ha permes coneixer quins son els parametres que tenen una major influencia en la qualitat dels resultats obtinguts en les simulacions de ray-tracing. S’ha arribat a dues conclusions: En primer lloc, simulacions espectrals no son rellevants per aplicacions solars termiques, a no ser que la dispersio del mirall depengui significativament de la longitud d’ona. En segon llos es imprescindible especificar al dependencia de l’angle d’incidencia dels materials optics per generar resultats acurats. En el cas de captadors concentradors biaxials, s’aplica el model de factoritzacio del modificador d’angle d’incidencia. Aquesta factoritzacio te sempre associat un cert error, ja que l’IAM no es en general factoritzable. S’ha caracteritzat l’error per quatre geometries de captadors diferents, comparant el models de factoritzacio amb les simulacions ray-tracing. Els resultats s’han presentat en funcio de la latitud geografica. La factoritzacio a l’espai ? -? es la que ofereix mes bons resultats en gairebe tots els casos analitzats. Quatre geometries diferents de captador foren analitzades per determinar la dependencia amb la temperatura de l’error de factoritzacio. S’ha demostrat que a mesura que s’incrementa la temperatura de treball, s’incrementa l’error relatiu del la factoritzacio, malgrat aixo, dins del rang de temperatures economicament viables, l’error es mante constant. Aixo es degut a que a mesura s’incrementa la temperatura, es redueixen les hores de treball, i per tant tambe les hores on el captador treballa sota els angles mes desfavorables per la factoritzacio. EnglishAccording to several studies, the installed capacity of solar thermal collectors to provide heat for industrial processes is going to increase significantly during the next decades. The great variety of designs and large range of operating temperatures of solar process collectors make their performance assessment challenging. Although the quasi-dynamic testing procedure has been designed for most types of collectors, it shows limitations or vagueness when dealing with medium-scaled collectors. This thesis analyzes some limitations, focusing mainly on the optical efficiency assessment. A powerful ray-tracing algorithm has been developed for the optical analyses in this thesis. The algorithm was used to carry out a sensitivity analysis of a Fresnel collector to achieve a better understanding of the most influential parameters in ray-tracing simulations. Two observations were made: First, spectral simulations are not relevant for solar thermal applications unless mirror scattering shows a very high dependency on the wavelength. Second, defining the incidence angle dependency of optical materials is crucial to produce accurate results. In the case of biaxial concentrating collectors, the incidence angle Modifier factorization model is commonly applied. This model inherently introduces errors by factorizing the underlying non-factorizable functions. The error was characterized for four different collector geometries by comparing factorization with ray-tracing simulations. Results have been presented as a function of geographical latitude. Factorization in the ? -? -space performed best in nearly all cases. Four different collector geometries were submitted to ray-tracing simulations in order to analyze the thermal dependency of the factorization error. It is shown that the relative error generally increases with higher operating temperatures, but within the economically viable temperature range it stays fairly constant. With higher temperatures the collector gradually stops operating beginning with moments when sun angles are least favorable for factorization.
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Influence of thermal losses on the incidence angle Modifier factorization approach
Solar Energy, 2016Co-Authors: Julian David Hertel, Víctor Martínez-moll, Ramon Pujol-nadalAbstract:Abstract Solar thermal applications for industries must be designed to operate at high temperature levels; however, the thermal dependency of the accuracy of the incidence angle Modifier factorization has not been sufficiently analyzed. In this study, the annually delivered energy based on both factorized and non-factorized incidence angle Modifier values were compared with each other. The integration was conducted for a typical meteorological year in Seville and Stockholm. Four collector types were considered: evacuated tube collector, MaReCo collector, Fresnel collector, and CCStaR collector. Thermal process parameters were shown to have an influence on the error made by the factorization approach; however, within the economically viable temperature range of an industrial heat application, this influence is not significant.
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Estimation of the influence of different incidence angle Modifier models on the biaxial factorization approach
Energy Conversion and Management, 2015Co-Authors: Julian David Hertel, Víctor Martínez-moll, Ramon Pujol-nadalAbstract:To minimize the experimental effort of assessing biaxial incidence angle characteristics of solar collectors with complex geometries, current testing standards (EN 12975-2, ASHRAE 93, ISO 9806:2013) recommend the factorization method proposed by McIntire (1982). Due to a lack of consensus, researchers in the low and high temperature fields of solar thermal have applied this model in very different ways, either referring to different radiation references (beam radiation on tilted surface vs. direct normal irradiance) or angle projections (θT-θL-domain vs. θT-θi-domain). In this study, the influence of each approach on the factorization error is estimated. Four different collector geometries were considered: compound parabolic collector, maximum reflector collector, linear Fresnel reflector, and fixed-mirror collector (Concentrating Collector with Stationary Reflector, CCStaR V2). The 3D incidence angle Modifier surface of each collector was calculated with a sophisticated in-house ray tracing tool and compared with the incidence angle Modifier surface constructed by various factorization models. The error was defined as difference between direct normal irradiance weighted annual integration of ray tracing and factorized incidence angle Modifier, given the collector’s location and orientation. This allows the deviations to be represented more intuitively by plotting the relative error over latitude. Factorization in the (θT,θi)-domain was shown to constantly yield accurate results even in the case of static collectors.
Björn Karlsson - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of a CPVT collector coupled with a wedge PVT receiver
Solar Energy, 2021Co-Authors: Diogo Cabral, Joao Gomes, Abolfazl Hayati, Björn KarlssonAbstract:Abstract This paper presents an experimental investigation of a photovoltaic-thermal solar collector (commonly known as PVT) that generates both electricity and heat from the same gross area. PVT solar collectors, in theory, achieve higher combined electrical and heat yields. Additionally, PVT enables a thermal coupling between PV cells and a heat transfer cooling medium. Electrical and thermal outdoor testing measurements have been performed on a low concentration PVT solar collector based on a parabolic reflector geometry with a wedge PVT receiver. Several outdoor experiments have been carried out and presented, such as daily instantaneous electrical and thermal performance efficiency diagrams, as well as optical efficiency charts. Moreover, an electrical Incidence Angle Modifier (for both transversal and longitudinal directions) assessment has been performed and presented. Furthermore, an overall heat loss coefficient of 4.1 W/m2.°C has been attained. A measured thermal optical and electrical efficiency of 59% and 8% have been achieved, respectively. Additionally, the placement of the wedge receiver shown to be very sensitive to high incidence angles, as the electrical transversal Incidence Angle Modifier factor decreases significantly after reaching its electrical peak efficiency at 10°.
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measurements of the electrical incidence angle Modifiers of an asymmetrical photovoltaic thermal compound parabolic concentrating collector
Engineering, 2013Co-Authors: Ricardo Bernardo, Henrik Davidsson, Niko Gentile, Joao Gomes, Christian Gruffman, Luis Chea, Mumba Chabu, Björn KarlssonAbstract:Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmetrical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle Modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maximum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.
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On the factorisation of incidence angle Modifiers for CPC collectors
Solar Energy, 1997Co-Authors: Mats Rönnelid, Bengt Perers, Björn KarlssonAbstract:Abstract It has been suggested earlier that the incidence angle Modifier Kτα for low concentrating collectors with tubular absorbers could be factorised according to Kτα(θt,θl) ∝ Kτα(θt,0)Kτα(0,θl, where θtand θl are the projected incidence angles in the transversal and longtitudinal projection planes, respectively. Ray-tracing calculations on low-concentrating CPC collectors with flat absorbers parallel to the cover show that a Kτα factorisation overestimates the annual delivered energy from the collector by about 4–5%, when compared to calculations using the full incidence angle Modifier. Data from outdoor testing has been used for characterization of incidence angle behaviour for a truncated CPC with a concentration of C = 1.56. Multiple linear regression analysis was used. This analysis technique makes feasible the determination of angular dependent incident angle Modifiers and is an efficient tool to use for all collectors which cannot be characterised by standard equations of the incidence angle dependence.
