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1.
  • Adeyefa, ZD, et al. (författare)
  • Spectral solar irradiance before and during a Harmattan dust spell
  • 1996
  • Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 57:3, s. 195-203
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of the ground-level spectral distributions of the direct, diffuse and global solar irradiance between 300 and 1100 nm were made at Akure (7.15°N, 5.5°E), Nigeria, in December 1991 before and during a Harmattan dust spell employing a spectroradiometer (LICOR LI-1800) with 6 nm resolution. The direct spectral solar irradiance which was initially reduced before the dust storm was further attenuated by about 50% after the spell. Estimated values of the Ångström turbidity coefficient β indicated an increase of about 146% of this parameter while the Ångström wavelength-exponent α decreased by about 65% within the 2-day study period. The spectral diffuse-to-direct and diffuse-to-global ratios suggest that the main cause of the significant reduction in solar irradiance at the surface was the scattering by the aerosol which led to an increase in the diffuse component. The global irradiance though reduced, was less sensitive to changing Harmattan conditions. It is recommended that solar energy devices that use radiation from Sun and sky be used under fluctuating Harmattan conditions. There are some deviations from the Ångström formula under very turbid Harmattan conditions which could be explained by the relative increase of the particle sizes.
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2.
  • Granqvist, C.-G., et al. (författare)
  • Recent advances in electrochromics for smart windows applications
  • 1998
  • Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 63:4, s. 199-216
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Electrochromic smart windows are able to vary their throughput of radiant energy by low-voltage electrical pulses. This function is caused by reversible shuttling of electrons and charge balancing ions between an electrochromic thin film and a transparent counter electrode. The ion transport takes place via a solid electrolyte. Charge transport is evoked by a voltage applied between transparent electrical conductors surrounding the electrochromic film/electrolyte/counter electrode stack. This review summarizes recent progress concerning: (i) calculated optical properties of crystalline WO3, (ii) electrochromic properties of heavily disordered W oxide and oxyfluoride films produced by reactive magnetron bias sputtering, (iii) novel transparent reactively sputter-deposited Zr-Ce oxide counter electrodes and (iv) a new proton-conducting antimonic-acid-based polymer electrolyte. Special in depth presentations are given on elastic light scattering from W-oxide-based films and of electronic band structure effects affecting opto-chronopotentiometry data in Zr-Ce oxide. The review also contains some new device data for an electrochromic smart window capable of very high optical transmittance.Electrochromic smart windows are able to vary their throughput of radiant energy by low-voltage electrical pulses. This function is caused by reversible shuttling of electrons and charge balancing ions between an electrochromic thin film and a transparent counter electrode. The ion transport takes place via a solid electrolyte. Charge transport is evoked by a voltage applied between transparent electrical conductors surrounding the electrochromic film/electrolyte/counter electrode stack. This review summarizes recent progress concerning: (i) calculated optical properties of crystalline WO3, (ii) electrochromic properties of heavily disordered W oxide and oxyfluoride films produced by reactive magnetron bias sputtering, (iii) novel transparent reactively sputter-deposited Zr-Ce oxide counter electrodes and (iv) a new proton-conducting antimonic-acid-based polymer electrolyte. Special in depth presentations are given on elastic light scattering from W-oxide-based films and of electronic band structure effects affecting opto-chronopotentiometry data in Zr-Ce oxide. The review also contains some new device data for an electrochromic smart window capable of very high optical transmittance.
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3.
  • Greijer Agrell, Helena, et al. (författare)
  • Degradation mechanisms in a dye-sensitized solar cell studied by UV-VIS and IR spectroscopy
  • 2003
  • Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 75:2, s. 169-180
  • Tidskriftsartikel (refereegranskat)abstract
    • By deliberately causing degradation of components in a dye-sensitized solar cell we have studied failure mechanisms of such cells. The dye, bis(tetrabutylammonium) cis–bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II), adsorbed to a nanostructured TiO2 film was studied with UV–VIS and IR spectroscopy after being exposed to visual and ultra-violet radiation, increased temperature, air, electrolyte, and water in the electrolyte. The thiocyanate ion ligand is lost in air, at temperatures equal to and above 135 °C, in electrolyte and possibly upon UV irradiation. The loss of the SCN− ligand in air was accelerated under visual illumination. From working electrodes immersed in the electrolyte or in degraded complete solar cells it was observed that the absorption peak from the thiocyanate ion ligand at around 2100 cm−1 had broadened, blue-shifted and decreased. One failure mechanism is thus that the thiocyanate ion ligand is lost from the dye together with the electrolyte. Together with water in the electrolyte (5 v%) the SCN− ligand is exchanged with H2O and/or OH−. The ligand exchange between SCN− and H2O/OH− was accelerated under visual illumination.
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4.
  • Nordell, Bo, et al. (författare)
  • High temperature solar heated seasonal storage system for low temperature heating of buildings
  • 2000
  • Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 69:6, s. 511-523
  • Tidskriftsartikel (refereegranskat)abstract
    • A preliminary study of a solar-heated low-temperature space-heating system with seasonal storage in the ground has been performed. The system performance has been evaluated using the simulation models TRNSYS and MINSUN together with the ground storage module DST. The study implies an economically feasible design for a total annual heat demand of about 2500 MWh. The main objective was to perform a study on Anneberg, a planned residential area of 90 single-family houses with 1080 MWh total heat demand. The suggested heating system with a solar fraction of 60% includes 3000 m2 of solar collectors but electrical heaters to produce peak heating. The floor heating system was designed for 30°C supply temperature. The temperature of the seasonal storage unit, a borehole array in crystalline rock of 60,000 m3, varies between 30 and 45°C over the year. The total annual heating costs, which include all costs (including capital, energy, maintenance etc.) associated with the heating system, were investigated for three different systems: solar heating (1000 SEK MWh−1), small-scale district heating (1100 SEK MWh−1) and individual ground-coupled heat pumps (920 SEK MWh−1). The heat loss from the Anneberg storage system was 42% of the collected solar energy. This heat loss would be reduced in a larger storage system, so a case where the size of the proposed solar heating system was enlarged by a factor of three was also investigated. The total annual cost of the solar heating system was reduced by about 20% to about 800 SEK MWh−1, which is lower than the best conventional alternative.
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5.
  • Adsten, Monika, et al. (författare)
  • Evaluation of CPC-collector designs for stand-alone, roof- or wall installation
  • 2005
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 79:6, s. 638-647
  • Tidskriftsartikel (refereegranskat)abstract
    • An asymmetrically truncated non-tracking compound parabolic concentrator type collector design concept has been developed. The collector type has a bi-facial absorber and is optimised for northern latitudes. The concept is based on a general reflector form that is truncated to fit different installation conditions. In this paper collectors for stand-alone, roof and wall mounting are studied. Prototypes of six different collectors have been built and outdoor tested. The evaluation gave high annual energy outputs for a roof mounted collector, 925 MJ/m2, and a stand-alone collector with Teflon, 781 MJ/m2, at an operating temperature of Top = 75 °C. A special design for roofs facing east or west was also investigated and gave an annual energy output of 349 (east) and 436 (west) MJ/m2 at Top = 75 °C. If a high solar fraction over the year is the objective, a load adapted collector with a high output during spring/fall and a low output during summer can be used. Such a collector had an output of 490 MJ/m2 at Top = 75 °C. Finally a concentrating collector for wall mounting was evaluated with an estimated annual output of 194 MJ/m2 at Top = 75 °C. The concentrator design concept can also be used for concentrators for PV-modules.
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6.
  • Adsten, M, et al. (författare)
  • Measurement of radiation distribution on the absorber in an asymmetric CPC collector
  • 2004
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 76:1-3, s. 199-206
  • Tidskriftsartikel (refereegranskat)abstract
    • A method to estimate the annual collected energy and the annual average optical efficiency factor is suggested. The radiation distribution on the absorber of an asymmetric CPC collector with a flat bi-facial absorber is measured for three different absorber mounting angles using a photo diode. The annual optical efficiency factors and a relative measure of the annual collected energy are determined for collectors with the absorber fin thickness 0.5 and 1 mm, and for a collector with a teflon convection suppression film mounted around the absorber. With the local optical efficiency factors and the annual incident solar energy distribution considered, the analysis indicates that the energy gain for a mounting angle of 20 is higher than for a collector with 65 absorber mounting angle. The annual collected energy is increased with 6-8% if the absorber fin thickness is increased from 0.5 to 1 mm. The annual average optical efficiency factor is relatively independent of the absorber mounting angle. It was found to be 0.87-0.88 for a collector with a 0.5 mm thick absorber fin and 0.92 for a collector with a 1 mm thick absorber fin or for a collector with 0.5 mm thick absorber fin with a teflon convection suppression film added. The low annual average optical efficiency factor is not caused by the uneven irradiance distribution but by the relatively high U-L-values. (C) 2003 Elsevier Ltd. All rights reserved.
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7.
  • Adsten, M, et al. (författare)
  • Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface
  • 2000
  • Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 68:4, s. 325-328
  • Tidskriftsartikel (refereegranskat)abstract
    • Tandem absorbers are often used in the design of solar absorbers for photo thermal conversion. They consist of a thin coating, selectively absorbing in the wavelength range of the solar spectrum, on a metal substrate. The optical performance of a tandem absorber depends on the optical constants and thickness of the absorbing coating and also on the reflectivity of the underlying metal. A very high solar absorptance is achieved when the coating has a non-uniform composition in the sense that the refractive index is highest closest to the metal substrate and then gradually decreases towards the front surface. This type of composition suppresses coating interference and gives a low front surface reflection if the refractive index at the front surface is low. We report on optical analysis of a, Solar absorber with a graded index coating of sputtered nickel-nickel oxide deposited on aluminium. The optical constants have been determined from reflectance, transmittance and ellipsometry data by fitting the data to a two-layer model of the coating. The optical constants of the two layers can be regarded as effective optical constants for the lower and upper part of the graded index coating respectively. It is found that the effective refractive index of the top layer is somewhat tower than for the base layer. The extinction coefficient is higher in the lower part of the coating. Both effective refractive index and extinction coefficient of the base layer increase monotonically with increasing wavelength as for metallic materials. (C) 2000 Elsevier Science Ltd. All rights reserved.
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8.
  • Aichmayer, Lukas, et al. (författare)
  • Preliminary design and analysis of a novel solar receiver for a micro gas-turbine based solar dish system
  • 2015
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 114:4, s. 378-396
  • Tidskriftsartikel (refereegranskat)abstract
    • The solar receiver is one of the key components of hybrid solar micro gas-turbine systems, which would seem to present a number of advantages when compared with Stirling engine based systems and photovoltaic panels. In this study a solar receiver meeting the specific requirements for integration into a small-scale (10 kWel) dish-mounted hybrid solar micro gas-turbine system has been designed with a special focus on the trade-offs between efficiency, pressure drop, material utilization and economic design. A situation analysis, performed using a multi-objective optimizer, has shown that a pressurized configuration, where the solar receiver is placed before the turbine, is superior to an atmospheric configuration with the solar receiver placed after the turbine. Based on these initial design results, coupled CFD/FEM simulations have been performed, allowing detailed analysis of the designs under the expected operating conditions. The results show that the use of volumetric solar receivers to provide heat input to micro gas-turbine based solar dish systems appears to be a promising solution; with material temperatures and material stresses well below permissible limits.
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9.
  • An, J., et al. (författare)
  • Stable and efficient PbS colloidal quantum dot solar cells incorporating low-temperature processed carbon paste counter electrodes
  • 2017
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 158, s. 28-33
  • Tidskriftsartikel (refereegranskat)abstract
    • Colloidal quantum dot (CQD) solar cells with a ZnO/PbS-TBAI/PbS-EDT/carbon structure were prepared using a solution processing technique. A commercially available carbon paste that was processed at low-temperatures was used as a counter electrode in place of expensive noble metals, such as Au or Ag, which are used in traditional PbS CQD solar cells. These CQD solar cells exhibited remarkable photovoltaic performance with a short circuit density (Jsc) of 25.6 mA/cm2, an open circuit voltage (Voc) of 0.45 V, a fill factor (FF) of 51.8% and a power conversion efficiency (PCE) as high as 5.9%. A reference device with an Au counter electrode had a PCE of 6.0%. The PCE of the carbon-containing CQD solar cell remained stable for 180 days when tested in ambient atmosphere, while the PCE of the Au-containing CQD solar cell lost 48.3% of its original value. Electrochemical impedance spectroscopy (EIS) demonstrated that holes within the PbS CQD were effectively transported to the carbon counter electrode.
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10.
  • Andersson, Kent, et al. (författare)
  • Zirconium nitride based transparent heat mirror coatings : preparation and characterisation
  • 1994
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 32:2, s. 199-212
  • Tidskriftsartikel (refereegranskat)abstract
    • Transparent heat mirror coatings based on thin zirconium nitride films have been prepared using reactive magnetron sputtering. The zirconium nitride films have been sandwiched between layers of zirconium oxide. It is shown that the multilayer configuration ZrO2/ZrN/ZrO2 can be used as solar control coatings on window glazings. A visible transmittance of around 60% and a thermal emittance lower than 0.2 can be obtained, and the ratio between visible transmittance and total solar transmittance can be as high as 1.7. The influence of substrate temperature on the optical quality of the films is evaluated and it is shown that the crystal structure of the first oxide layer is of importance for the optical quality of the nitride. The influence of preparation conditions and accelerated ageing has been modelled using the optical constants of thin films prepared under identical conditions as the films in the multilayer coatings.
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11.
  • Andersson, Viktor, et al. (författare)
  • Full day modelling of V-shaped organic solar cell
  • 2011
  • Ingår i: Solar Energy. - : Elsevier Science B.V., Amsterdam.. - 0038-092X .- 1471-1257. ; 85:6, s. 1257-1263
  • Tidskriftsartikel (refereegranskat)abstract
    • Folded and planar solar cells are examined with optical simulations, with the finite element method. The maximum photocurrent densities during the full day are compared between cells of different geometries and tilting angles. The change of incident angle and spectrum over time are handled in this analysis. The results show that the light trapping effect of the folded cell makes these cells show higher maximum photocurrent densities than the planar cells during all hours of the day. This is the case for both single and tandem cells. The results also indicate that balancing the currents in the tandem cells by adjusting the active layer thickness may be more cumbersome with the folded tandem cells than the stacked planar cells.
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12.
  • Bader, Sebastian, 1984-, et al. (författare)
  • One-diode photovoltaic model parameters at indoor illumination levels – A comparison
  • 2019
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 180, s. 707-716
  • Tidskriftsartikel (refereegranskat)abstract
    • Models of photovoltaic devices are used to compare the properties of photovoltaic cells and panels, and to predict their I-V characteristics. To a large extent, modeling methods are based on the one-diode equivalent circuit. Although much research exists on the implementation and evaluation of these methods for typical outdoor conditions, their performance at indoor illumination levels is largely unknown. Consequently, this work performs a systematic study of methods for the parameter extraction of one-diode models under indoor conditions. We selected, reviewed and implemented commonly used methods, and compared their performance at different illumination levels. We have shown that most methods can achieve good accuracies with extracted parameters regardless of the illumination condition, but their accuracies vary significantly when the parameters are scaled to other conditions. We conclude that the physical interpretation of extracted parameters at low illumination is to a large extent questionable, which explains errors based on standard scaling approaches. 
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13.
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14.
  • Bashir, Amna, et al. (författare)
  • Cu-doped nickel oxide interface layer with nanoscale thickness for efficient and highly stable printable carbon-based perovskite solar cell
  • 2019
  • Ingår i: Solar Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-092X .- 1471-1257. ; 182, s. 225-236
  • Tidskriftsartikel (refereegranskat)abstract
    • The power conversion efficiency (PCE) of hole conductor free carbon-based perovskite solar cells (PSCs) is restricted by the poor charge extraction and recombination losses at the carbon-perovskite interface. For the first time we successfully demonstrated incorporation of thin layer of copper doped nickel oxide (Cu:NiOx) nanoparticles in carbon-based PSCs, which helps in improving the performance of these solar devices. Cu:NiOx nanoparticles have been synthesized by a facile chemical method, and processed into a paste for screen printing. Extensive X-ray Absorption Spectroscopy (XAS) analysis elucidates the co-ordination of Cu in a NiOx matrix and indicates the presence of around 5.4% Cu in the sample. We fabricated a monolithic perovskite module on a 100 cm(2) glass substrate (active area of 70 cm(2)) with a thin Cu:NiOx layer (80 nm), where the champion device shows an appreciated power conversion efficiency of 12.1% under an AM 1.5G illumination. To the best of our knowledge, this is the highest reported efficiency for such a large area perovskite solar device. I-V scans show that the introduction of Cu:NiOx mesoporous scaffold increases the photocurrent, and yields fill factor (FF) values exceeding 57% due to the better interface and increased hole extraction efficiency. Electrochemical Impedance Spectroscopy (EIS) results reinforce the above results by showing the reduction in recombination resistance (R-rec) of the PSCs that incorporates Cu:NiOx interlayer. The perovskite solar modules with a Cu:NiOx layer are stable for more than 4500 h in an ambient environment (25 degrees C and 65% RH), with PCE degradation of less than 5% of the initial value.
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15.
  • Bright, Jamie M., et al. (författare)
  • Improved satellite-derived PV power nowcasting using real-time power data from reference PV systems
  • 2018
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 168, s. 118-139
  • Tidskriftsartikel (refereegranskat)abstract
    • Rapid growth in the global penetration of solar photovoltaic (PV) systems means electricity network operators and electricity generators alike are increasingly concerned with the short-term solar forecasting (nowcasting) of solar irradiance. This paper proposes a methodology that considers a varying number of available reference PV systems for supporting satellite-derived PV power real-time nowcasting. We evaluate conventional satellite-only and upscaling-only PV fleet estimate methodologies and compare them to two newly developed correction and hybrid cases. When using only a single reference PV system to estimate the aggregated power of 48 independent target PV systems for the location of Canberra, Australia; we show that the newly proposed correction or hybrid cases improve the performance of the satellite-derived PV power estimate medians in terms of MBE, rMBE, RMSE and rRMSE from 0.031 W/W-p, 7.46%, 0.079 W/W-p and 23.4%, down to 0.006 W/W-p,-0.711%, 0.068 W/W-p and 20.0%, representing relative improvements of 80.6%, 90.5%, 13.9% and 14.5%, respectively. Similarly, when using 30 reference PV systems, we report median improvements from 0.036 W/W-p, 8.25%, 0.083 W/W-p and 24.8%, down to 0.01 W/W-p, 1.41%, 0.049 W/W-p and 11.4%, representing relative improvements of 72.2%, 82.9%, 41.0% and 54.0%, respectively. We discuss the fundamental challenges facing the use of reference PV systems, satellite-derived power estimates, combining the two data sources, and the knowledge required to address these issues. We ultimately conclude that combining satellite-based PV power estimates with data from reference PV systems is always more beneficial than either on their own.
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16.
  • Brinkworth, B. J., et al. (författare)
  • Design procedure for cooling ducts to minimise efficiency loss due to temperature rise in PV arrays
  • 2006
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 80:1, s. 89-103
  • Tidskriftsartikel (refereegranskat)abstract
    • The principal variable to be fixed in the design of a PV cooling duct is its depth, and hence the hydraulic diameter of its cross-section D. Analysis of the flow and heat transfer in the duct under still-air (buoyant flow) conditions, when the temperature rise is greatest, is validated by measurements on a full-scale test rig. It is shown that there is an optimum value of this design variable, such that for an array of length L the minimum temperature occurs when the ratio L/D is about 20. The optimum value is not affected much by other quantities, including the slope of the array. In practical situations, the flow is obstructed by devices across the duct inlet and outlet to exclude insects, birds and rain, and by structural support members crossing the duct interior. It is shown that the latter are no cause for concern, since the effect of the reduction in the flow-rate due to their presence is more than offset by an increase in heat transfer through additional turbulent mixing. It is also shown that array temperatures are strongly reduced by wind effects, which increase both the heat lost from the front surface of the array and by enhancement of the flow in the duct. Though the trends are clear, limitations are encountered in the present state of knowledge in both areas.
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17.
  • Broman, Lars, et al. (författare)
  • Parabolic dish concentrators approximated by simple surfaces
  • 1996
  • Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 57:4, s. 317-321
  • Tidskriftsartikel (refereegranskat)abstract
    • Two different concentrating mirrors have been constructed that resemble parabolic dish reflectors. Both mirrors are made of slightly curved strips of flat, bendable material. The strips of the most simplified mirror have only large-radius circles and straight lines as boundaries. The necessary equations for making the mirrors are given. Also a simple way to make a stiff, lightweight frame and support for the mirror strips has been developed. Models of the mirrors have been built and successfully used for cooking and baking.
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18.
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19.
  • Cabral, Diogo, et al. (författare)
  • Electrical and thermal performance evaluation of symmetric truncated C-PVT trough solar collectors with vertical bifacial receivers
  • 2018
  • Ingår i: Solar Energy. - : Elsevier Ltd. - 0038-092X .- 1471-1257. ; 174, s. 683-690
  • Tidskriftsartikel (refereegranskat)abstract
    • One way to reduce solar collectors’ production costs is to use concentrators that increase the output per photovoltaic cell. Concentrating collectors re-direct solar radiation that passes through an aperture into an absorber/receiver. Symmetrical truncated non-tracking C-PVT trough collectors based on a parabola and compound parabolic concentrator (CPC) geometries have been developed. The collector type has a central vertical bifacial (fin) receiver and it was optimized for lower latitudes. In this paper, the electrical and thermal performance of symmetric truncated non-tracking low concentrator PVT solar collectors with vertical bifacial receivers is analysed, through a numerical ray-tracing model software and a multi-paradigm numerical computing environment. A thermal (quasi-dynamic testing method for liquid heating collectors described in the international standard for solar thermal collectors ISO 9806:2013) and electrical performance models were implemented to evaluate the design concepts. The evaluation was made for heating Domestic Hot Water for a Single Family House in Fayoum (Egypt), where CPC geometries with a concentration factor of 1.6 achieved 8 to 13%rel higher energy yields (in kWh/m2/year) than the Pure Parabola geometries.
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20.
  • Cabral, Diogo, et al. (författare)
  • Experimental investigation of a CPVT collector coupled with a wedge PVT receiver
  • 2021
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 215, s. 335-345
  • Tidskriftsartikel (refereegranskat)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 alow 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 IncidenceAngle 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 AngleModifier factor decreases significantly after reaching its electrical peak efficiency at 10◦.
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21.
  • Cabral, Diogo, et al. (författare)
  • Performance Evaluation of Non-Uniform Illumination on a Transverse Bifacial PVT Receiver in Combination with a CPC Geometry
  • 2019
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 194, s. 696-708
  • Tidskriftsartikel (refereegranskat)abstract
    • PVT collectors co-generate electricity and heat from the same gross area, thus achieving higher combined heat and electric yields. A comprehensive evaluation has been carried out on non-uniform solar irradiation profile distributions on four symmetric low concentration CPC PVT (LCPVT) solar collector design concepts. Additionally, an electrical and thermal performance evaluation of symmetric truncated LCPVT solar collectors based on a CPC reflector geometry with a central transverse bifacial PVT receiver has been carried out, through a numerical ray-tracing model software and a multi-paradigm numerical computing environment software. A simplified thermal (quasi-dynamic testing method for liquid heating collectors described in the international standard for solar thermal collectors ISO 9806:2017) and electrical performance models were employed to evaluate the LCPVT design concepts. The evaluation was carried out for heating Domestic Hot Water (DHW) for a Single Family House (SFH) in Fayoum (Egypt), where energy yields between 351 and 391 kWh/m2/year have been achieved. The non-uniform solar irradiation assessment showed that the PV cells are exposed to high levels of radiation due to the specific reflector geometry. Furthermore, the study showed that the CPC geometries are very sensitive to the shading effect, as partial shadowing is substantial for high incidence angles.
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22.
  • Campana, Pietro Elia, 1984-, et al. (författare)
  • A gridded optimization model for photovoltaic applications
  • 2020
  • Ingår i: Solar Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-092X .- 1471-1257. ; 202, s. 465-484
  • Tidskriftsartikel (refereegranskat)abstract
    • This study aims to develop a gridded optimization model for studying photovoltaic applications in Nordic countries. The model uses the spatial and temporal data generated by the mesoscale models STRANG and MESAN developed by the Swedish Meteorological and Hydrological Institute. The model is developed based on the comparison between five irradiance databases, three decomposition models, two transposition models, and two photovoltaic models. Several techno-economic and environmental aspects of photovoltaic systems and photovoltaic systems integrated with batteries are investigated from a spatial perspective. CM SAF SARAH-2, Engerer2, and Perez1990 have shown the best performances among the irradiance databases, and decomposition and transposition models, respectively. STRANG resulted in the second-best irradiance database to be used in Sweden for photovoltaic applications when comparing hourly global horizontal irradiance with weather station data. The developed model can be employed for carrying out further detailed gridded techno-economic assessments of photovoltaic applications and energy systems in general in Nordic countries. The model structure is generic and can be applied to every gridded climatological database worldwide.
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23.
  • Campana, Pietro Elia, et al. (författare)
  • Optimization and assessment of floating and floating-tracking PV systems integrated in on- and off-grid hybrid energy systems
  • 2019
  • Ingår i: Solar Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-092X .- 1471-1257. ; 177, s. 782-795
  • Tidskriftsartikel (refereegranskat)abstract
    • Considering the targets of Thailand in terms of renewable energy exploitation and decarbonization of the shrimp farming sector, this work evaluates several scenarios for optimal integration of hybrid renewable energy systems into a representative shrimp farm. In particular, floating and floating-tracking PV systems are considered as alternatives for the exploitation of solar energy to meet the shrimp farm electricity demand. By developing a dynamic techno-economic simulation and optimization model, the following renewable energy systems have been evaluated: PV and wind based hybrid energy systems, off-grid and on-grid PV based hybrid energy systems, ground mounted and floating PV based hybrid energy systems, and floating and floating-tracking PV based hybrid energy systems. From a water-energy nexus viewpoint, floating PV systems have shown significant impacts on the reduction of evaporation losses, even if the energy savings for water pumping are moderate due to the low hydraulic head. Nevertheless, the study on the synergies between water for food and power production has highlighted that the integration of floating PV represents a key solution for reducing the environmental impacts of shrimp farming. For the selected location, the results have shown that PV systems represent the best renewable solution to be integrated into a hybrid energy system due to the abundance of solar energy resources as compared to the moderate wind resources. The integration of PV systems in off-grid configurations allows to reach high renewable reliabilities up to 40% by reducing the levelized cost of electricity. Higher renewable reliabilities can only be achieved by integrating energy storage solutions but leading to higher levelized cost of electricity. Although the floating-tracking PV systems show higher investment costs as compared to the reference floating PV systems, both solutions show similar competiveness for reliabilities up to 45% due to the higher electricity production of the floating-tracking PV systems. The higher electricity production from the floating-tracking PV systems leads to a better competitiveness for reliabilities higher than 90% due to lower capacity requirements for the storage systems.
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24.
  • Carlsson, Bo (författare)
  • Phase change behaviour of some latent heat storage media based on calcium chloride hexahydrate
  • 2009
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 83:4, s. 485-500
  • Tidskriftsartikel (refereegranskat)abstract
    • Phase change behaviour of pure and some chemically modified calcium chloride hexahydrate materials suggested in the literature as suitable heat storage media was studied in storage systems with a low degree of mixing in order to evaluate their long-term reversibility. The influence of gravitation on the phase change properties of the pure system was elaborated by determining local salt concentrations in the liquid phase and changes in the volume of the system during repeated melting and crystallization, whereby the amounts of the different phases being present could be assessed. It was found that thermo gravitational effects are of minor importance in generating salt concentration gradients in the liquid phase when compared to the concentration gradients resulting from the sedimentation of the formed tetrahydrate and the hexahydrate during the phase change reactions. Due to these effects it was not possible to prevent irreversible tetrahydrate formation and deterioration in heat storage capability by adding a surplus of water to the hexahydrate materials, if seeds for the tetrahydrate were present during repeated melting and crystallization. Upon addition of SrCl(2) center dot 6H(2)O a solid solution of the two hexahydrates is formed and as a result the formation of the tetrahydrate is suppressed. Due to irreversible formation of SrCl(2) center dot 6H(2)O a state of true congruent melting seems, however, not possible to reach. Phase segregation effects also in this case lead to irreversible calcium chloride tetrahydrate formation if seeds for the latter are added during repeated melting and crystallization. If Ca(OH)(2) is also added, the tetrahydrate formation can be further suppressed. But, even in this case, irreversible tetrahydrate formation can not be prevented if the composition of the liquid phase corresponds to the hexahydrate. On addition of 5 wt% KCl or 5 wt% KCl + 2 wt% SrCl(2) center dot 6H(2)O or 5 wt% KCl + 0.4 wt% NaCl, repeated melting and crystallization in the presence of seeds of the tetrahydrate can, however, be carried out without irreversible formation of the latter occurs. In the heat storage system CaCl(2) center dot 6H(2)O + 5 wt% KCl, formation of tetrahydrate is observed but its rate of dissolution is found considerably faster than in the pure hexahydrate system. It was concluded that with those modified calcium chloride hexahydrate systems reversible phase change cycling can be performed and therefore there is for example no the need for thickener agents to be added to avoid irreversible tetrahydrate formation successively reducing heat storage capability of systems in those cases.
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25.
  • Carlsson, Bo, 1946-, et al. (författare)
  • Replacing traditional materials with polymeric materials in solar thermosiphon systems : Case study on pros and cons based on a total cost accounting approach
  • 2016
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 125, s. 294-306
  • Tidskriftsartikel (refereegranskat)abstract
    • The pros and cons of replacing traditional materials with polymeric materials in solar thermosiphon systems were analysed by adopting a total cost accounting approach.In terms of climatic and environmental performance, polymeric materials reveal better key figures than traditional ones like metals. In terms of present value total cost of energy, taking into account functional capability, end user investment cost, O&M cost, reliability and climatic cost, the results suggest that this may also be true when comparing a polymeric based thermosiphon system with a high efficient thermosiphon system of conventional materials for DHW production in the southern Europe regions. When present values for total energy cost are assessed for the total DHW systems including both the solar heating system and the auxiliary electric heating system, the difference in energy cost between the polymeric and the traditional systems is markedly reduced.The main reason for the difference in results can be related to the difference in thermal performance between the two systems. It can be concluded that the choice of auxiliary heating source is of utmost importance for the economical competiveness of systems and that electric heating may not be the best choice.
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26.
  • Chen, Yang, et al. (författare)
  • Dynamic simulation of a solar-driven carbon dioxide transcritical power system for small scale combined heat and power production
  • 2010
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 84:7, s. 1103-1110
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon dioxide is an environmental benign natural working fluid and has been proposed as a working media for a solar-driven power system In the current work, the dynamic performance of a small scale solar-driven carbon dioxide power system is analyzed by dynamic simulation tool TRNSYS 16 (Klein et al., 2004) and Engineering Equation Solver (EES) (Klein, 2004) using co-solving technique Both daily performance and yearly performance of the proposed system have been simulated Different system operating parameters, which will influence the system performance, have been discussed. Under the Swedish climatic condition, the maximum daily power production is about 12 kW h and the maximum monthly power production is about 215 kW h with the proposed system working conditions Besides the power being produced, the system can also produce about 10 times much thermal energy. which can be used for space heating, domestic hot water supply or driving absorption chillers The simulation results show that the proposed system is a promising and environmental benign alternative for conventional low-grade heat source utilization system (C) 2010 Elsevier Ltd All rights reserved.
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27.
  • Dabaieh, Marwa, et al. (författare)
  • An urban living lab monitoring and post occupancy evaluation for a Trombe wall proof of concept
  • 2019
  • Ingår i: Solar Energy. - : International Solar Energy Society. - 0038-092X .- 1471-1257. ; 193, s. 556-567
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to extreme climate change events, achieving indoor thermal comfort has become a significant challenge in remote desert areas; particularly with the increasing number of energy shortages in these areas. This study uses participatory action research methodology by means of an occupant centred approach for the design and construction of a Trombe wall system, suitable for passive heating and cooling in hot arid climates. The Trombe wall is used as a low-tech retrofitting passive solution to provide deprived communities in off-grid desert areas with a better indoor climate. The paper presents data from one year of monitoring and post occupancy evaluation for the Trombe wall installed as a retrofit in a residential unit in Sinai, Egypt as a proof of concept. Available affordable local materials were of main concern because of the project’s remote location in a mountainous desert area with very limited natural resources. The idea was to involve the local community in the different phases of the project, then train them onsite on how to use the Trombe wall system. Results indicate that the use of the Trombe wall did in fact enhance indoor heating and cooling loads. In addition, the direct involvement of the local inhabitants proved to have a positive impact on the Trombe wall’s performance and efficiency. The discussion elaborates on key lessons learned and challenges faced from the urban living lab experience presented in the study. Lastly, recommendations for further implementation of the passive Trombe wall system are presented.
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28.
  • Dabaieh, Marwa, et al. (författare)
  • Going green in architectural education : An urban living lab experiment for a graduation green design studio in Saint Catherine, Egypt
  • 2017
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 144, s. 356-366
  • Tidskriftsartikel (refereegranskat)abstract
    • Given the current energy crises, recent efforts have been directed at bringing energy efficiency and environmental awareness across the board into architectural education in Egypt. Although interest in sustainable design teaching and learning started more than 20 years ago at both post graduate and undergraduate level in Egypt, ecological illiteracy persists in architecture education. There is a large gap between what our schools of architecture offer, what the regulations currently specify, and what the market demands. This paper investigates the role of the graduation design studio in rooting an understanding of sustainability in architectural higher education, taking an experimental design studio case as an example. During this studio, the students developed a range of skills and techniques that were of value to their graduation projects and which will stand by them later as architects in the future. Students were able to experience climatic conditions and building technology in a specific context and associated with specific local vernacular architecture. Such experience was used to develop new adaptive and responsive climatic architecture approaches by means of physical hands on test cell models in a living lab environment. The design studio focuses on passive solar approaches suitable for a hot arid climate. The paper aims to show how this design studio could be a pilot model for green architectural education in Egypt.
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29.
  • Dabaieh, Marwa, et al. (författare)
  • Roof top PV retrofitting: A rehabilitation assessment towards nearly zero energy buildings in remote off-grid vernacular settlements in Egypt
  • 2016
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 123:123, s. 160-173
  • Tidskriftsartikel (refereegranskat)abstract
    • Vernacular buildings in Egypt express a variety of passive low-tech approaches in design and construction to achieve human comfort and fulfil inhabitants’ requirements. They have been devised to suit living in regions where local inhabitants had to invent various passive building strategies to live under severe local climatic conditions without depending on fossil fuels. This paper discusses a retrofitting approach for off-grid vernacular buildings in the Western Desert of Egypt. The study hypothesis argues that, when retrofitted and equipped with renewable energy solutions, vernacular structures can act as nearly zero energy buildings. A post occupancy evaluation was used as an assessment tool for two pilot projects that served as case studies. Results showed that combining vernacular passive strategies with affordable active renewables such as roof top solar panels results in a hybrid energy efficient retrofitting solution for deprived off-grid vernacular buildings. The intention is for the results to act as a basis for future retrofitting that would take into account the challenges and obstacles inherent in such work. This is an aim capable of contributing to a reduction of energy consumption that would also encourage retrofitting using renewable solutions for existing housing stock in Egypt.
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30.
  • Dabaieh, Marwa, et al. (författare)
  • Ventilated Trombe wall as a passive solar heating and cooling retrofitting approach : a low-tech design for off-grid settlements in semi-arid climates
  • 2015
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 122, s. 820-833
  • Tidskriftsartikel (refereegranskat)abstract
    • In the coming years, it is anticipated that if we continue with the same pace of energy consumption, communities will continue to face three major challenges; a mounting increase in energy demands, pollution, and global warming. On a local scale, Egypt is experiencing one of its most serious energy crises in decades. The energy consumed in indoor cooling and heating is the biggest portion of total energy consumption in residential buildings. This paper is an experimental simulation study for building retrofitting in off-grid settlements in semi-arid climates, using Trombe wall as a low-tech passive heating and cooling solution. In this study, we made developments to the conventional classic Trombe wall using occupant-centered design and living lab experimental methods. The thermal efficiency of the proposed Trombe wall design is simulated during winter and summer peaks. In the proposed design we used gray paint instead of typical black paint in addition to 15 cm reversible natural wool insulation and two 3 mm thick roll-up wool curtains. The new design reduced the heating load by 94% and reduced the cooling load by 73% compared to the base case with an annual energy savings of 53,631 kW h and a reduction in CO2 emissions of 144,267 kg of CO2. The living lab test proved that the proposed design of the Trombe wall is economically viable and the payback time is 7 months. It is recommended that the proposed design be monitored for a whole year to have an accurate assessment of its efficiency. A post occupancy evaluation is also needed to measure local residents’ acceptance and perceived comfort after retrofitting.
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31.
  • Dahm, Jochen, et al. (författare)
  • Evaluation of storage configurations with internal heat exchangers
  • 1998
  • Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 62:6, s. 407-417
  • Tidskriftsartikel (refereegranskat)abstract
    • An international standard, ISO/DP 9459-4A, 1996 has been proposed to establish a uniform standard of quality for small solar heating systems. In this proposal, system components are tested separately and total system performance is calculated using system simulations based on validated component model parameter values. Another approach is to test the whole system in operation under representative conditions, where the results can be used as a measure of the general system performance. Component testing and system simulation is flexible, but requires an accurate and reliable simulation model. The advantage of system testing is that it is not dependent on simulations and that it shows the actual system performance. Its disadvantage is that it is restricted to the boundary conditions for the test. The heat store is a key component concerning system performance. Thus, this work focuses on the storage system consisting of store, electrical auxiliary heater, internal heat exchangers (solar and load loops) and tempering valve. Four different storage system configurations with a volume of 7501 were tested in an indoor system test using a statistically generated six-day test sequence and a solar collector simulator. A store component test and system simulation was carried out on one of the four configurations, applying the proposed standard for stores, ISO/DP 9459-4A, 1996 and the MULTIPORT store model. Three test sequences for internal load side heat exchangers, not in the proposed ISO standard, were also carried out. This paper discusses the results of the indoor system test, the store component test, the validation of the store model parameter values and the system simulations. (C) 1998 Elsevier Science Ltd. All rights reserved.
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32.
  • Delgado-Bonal, Alfonso, et al. (författare)
  • Martian Top of the Atmosphere 10–420 nm spectral irradiance database and forecast for solar cycle 24
  • 2016
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 134, s. 228-235
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultraviolet radiation from 10 to 420 nm reaching Mars Top of the Atmosphere (TOA) and surface is important in a wide variety of fields such as space exploration, climate modeling, and spacecraft design, as it has impact in the physics and chemistry of the atmosphere and soil. Despite the existence of databases for UV radiation reaching Earth TOA, based in space-borne instrumentation orbiting our planet, there is no similar information for Mars. Here we present a Mars TOA UV spectral irradiance database for solar cycle 24 (years 2008–2019), containing daily values from 10 to 420 nm. The values in this database have been computed using a model that is fed by the Earth-orbiting Solar Radiation and Climate Experiment (SORCE) data. As the radiation coming from the Sun is not completely isotropic, in order to eliminate the geometrically related features but being able to capture the general characteristics of the solar cycle stage, we provide 3-, 7- and 15-days averaged values at each wavelength. Our database is of interest for atmospheric modeling and spectrally dependent experiments on Mars, the analysis of current and upcoming surface missions (rovers and landers) and orbiters in Mars. Daily values for the TOA UV conditions at the rover Curiosity location, as well as for the NASA Insight mission in 2016, and ESA/Russia ExoMars mission in 2018 are provided.
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33.
  • Delgado-Bonal, Alfonso, et al. (författare)
  • Solar cell temperature on Mars
  • 2015
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 118, s. 74-79
  • Tidskriftsartikel (refereegranskat)abstract
    • The operating temperature of a solar cell determines its efficiency and performance. This temperature depends on the materials used to build the cell but also on the environmental variables surrounding it (i.e., radiation, ambient temperature, wind speed and humidity). Several equations have been proposed to calculate this temperature, depending on these variables. Also, for Earth conditions, simplifiedequations have been developed, but are not valid for other planets, as Mars, where the environmental conditions are extremely different.In this paper, we develop a simplified equation to calculate the temperature of a solar cell under Mars environmental conditions and discuss the effect that altitude and wind on Mars might have on the solar cell temperature. The correct determination of the operating temperature of the cell will help to optimize the design of the next solar cell powered rovers for the exploration of Mars.
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34.
  • Duarte, Willian M., et al. (författare)
  • Refrigerants selection for a direct expansion solar assisted heat pump for domestic hot water
  • 2019
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 184:May, s. 527-538
  • Tidskriftsartikel (refereegranskat)abstract
    • An important step during a project of a heat pump system is choosing a more suitable refrigerant. This paper presents a comparative study among refrigerants for a small direct expansion solar assisted heat pump (DX-SAHP). The mathematical model used in this study is presented in detail and validated from an experimental setup. The R134a is the reference and the refrigerants with low GWP are R290, R600a, R744 and R1234yf. The results show that R290 has better COP than others refrigerants for solar radiation between 300 W/m2 and 700 W/m2, as well as for environment temperature between 10 C and 35 C. On the other hand, for solar radiation less than 50 W/m2, the R134a has better COP than R290. TEWI (Total Equivalent Warming Impact) analysis indicates that the indirect emission is the most important effect, and then, the TEWI results almost followed the COP outcome. A parametric analysis was conducted to evaluate the influence of the CO2 emission factor for producing electricity. In countries with higher emission factor, the refrigerant with the best COP has the best TEWI. The influence of wind speed and ambient temperature in COP of a DX-SAHP using R290 were more relevant in low solar radiation
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35.
  • Ehnberg, Jimmy, 1976, et al. (författare)
  • Simulation of global solar radiation based on cloud observations
  • 2005
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 78:1, s. 157-162
  • Tidskriftsartikel (refereegranskat)abstract
    • A stochastic model for simulating global solar radiation on a horizontal surface has been developed for use in power systems reliability calculations. The importance of an appropriate model for global solar radiation has increased with the increased use of photovoltaic power generation. The global solar radiation shows not only regular yearly and daily variations but also a random behaviour. The yearly and daily variations can be described in a deterministic way while the random behaviour has a high correlation with the state of the atmosphere. The astronomic effects can easily be described mathematical with only some minor simplifications but the atmospheric effects are more complicated to describe. The transmittivity of solar radiation in the atmosphere depends on various factors, e.g. humidity, air pressure and cloud type. By using cloud observations as input for the simulations, the local meteorological conditions can be accounted for. The model is usable for any geographical location if cloud observations are available at the location or at locations with similar climatological conditions. This is especially useful for development countries where long-term solar radiation measurement can be hard to obtain. Cloud observations can be performed without any expensive equipment and have been a standard parameter for many years throughout the world. Standard observations are done according to the Oktas-scale. It is the interval between observations that sets the resolution of the simulation: the observations are normally only every hour or every third hour. The model can easily be combined with cloud coverage simulations, has been proposed, for a more general model. For some calculations higher resolution may be needed. This can be obtained by including a stochastic model for the short-term variations and simple model has been proposed. Errors and limitations of the model are estimated and discussed.
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36.
  • Englund, Sven, et al. (författare)
  • Cu2ZnSn(S,Se)4 from annealing of compound co-sputtered precursors : Recent results and open questions
  • 2018
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 175, s. 84-93
  • Tidskriftsartikel (refereegranskat)abstract
    • Cu2ZnSn(S,Se)(4) (CZTS) thin film solar cells have reached efficiencies of up to 12.6% and current research is focused on understanding reasons for device limitations. At Uppsala University, a CZTS synthesis route based on compound sputtering and annealing in elemental vapors is used. Variation of chemical composition and annealing conditions is used as a tool to try to understand defect-related material- and device properties. Front and back contacts are also studied with focus on energy band matching at the hetero-interface using atomic layer deposition buffer layers and chemical stability of the back contact. In this review, we discuss recent work from our group, with reference to related work in the literature and with regards to areas for future work.
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37.
  • Ferruzza, D., et al. (författare)
  • Impact of steam generator start-up limitations on the performance of a parabolic trough solar power plant
  • 2018
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 169, s. 255-263
  • Tidskriftsartikel (refereegranskat)abstract
    • Concentrating solar power plants are an attractive option in the renewable energy generation market. The possibility of integrating relatively cheap forms of energy storage makes them a desirable solution when power generation must be readily available at any time of the day. Solar power plants typically start-up and shut down every day, so in order to maximize their profitability, it is necessary to increase their flexibility in transient operation and to initiate power generation as rapidly as possible. Two of the key components are the steam generator and steam turbine and the rates at which they can reach operational speed are limited by thermo-mechanical constraints. This paper presents an analysis of the effects of the thermal stress limitations of the steam generator and steam turbine on the power plant start-up, and quantifies their impact on the economy of the system. A dynamic model of a parabolic trough power plant was developed and integrated with a logic controller to identify start-up limitations, and subsequently the dynamic model was integrated in a techno-economic tool previously developed by the authors. The plant was analysed under two different operating strategies, namely solar-driven and peak-load. The results indicate that for steam generator hot start-ups, a 1.5% increase in peak-load electricity production would be achieved by doubling the maximum allowable heating rate of the evaporator. No useful increase would be achieved by increasing the rates beyond a limit of 7–8 K/min, as the turbine would then be the main limiting component during start-up. Similar conclusions can be drawn for the solar-driven case, for which the solar field and the energy source availability would pose the major constraint when starting up the steam generator system.
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38.
  • Ferruzza, Davide, et al. (författare)
  • Optimal start-up operating strategies for gas-boosted parabolic trough solar power plants
  • 2018
  • Ingår i: Solar Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-092X .- 1471-1257. ; 176, s. 589-603
  • Tidskriftsartikel (refereegranskat)abstract
    • Concentrating solar power plants are taking an increasing share in the renewable energy generation market. Parabolic trough is one of such technologies and the most commercially mature. However, this technology still suffers from technical challenges that need to be addressed. As these power plants experience daily start-up procedures, the optimal performance in transient operation needs to be considered. This paper presents a performance based modelling tool for a gas-boosted parabolic trough power plant. The objective of the paper is to define an optimal operational strategy of the power plant start-up procedure with the aim of minimizing its fuel consumption while at the same time maximizing its electric energy output, taking into account all the thermo-mechanical constraints involved in the procedure. Heating rate constraints of the steam generator and the booster heater, and the steam turbine start-up schedule were considered. The simulation model was developed based on a power plant located near Abu Dhabi, and was validated against real operational data with a maximum integral relative deviation of 4.3% for gross electric energy production. A multi-objective optimization was performed for a typical operating week during winter and spring weather conditions. The results suggest that in order to minimize the fuel consumption and at the same time maximize the electric energy production, an evaporator heating rate of 6 K/min is an optimal value both for winter and spring conditions.
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39.
  • Flores-Diaz, Natalie, et al. (författare)
  • Neutral organic redox pairs based on sterically hindered hydroquinone/benzoquinone derivatives for dye-sensitized solar cells
  • 2018
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 167, s. 76-83
  • Tidskriftsartikel (refereegranskat)abstract
    • Substituted derivatives of hydroquinone/benzoquinone were studied as organic redox mediators in the electrolyte for dye-sensitized solar cells (DSSCs). Thus, di-tert-butylhydroquinone (DTHQ), thymohydroquinone (ThymHQ) and phenylhydroquinone (PhHQ), were combined with their oxidized counterparts to form the pairs DTHQ/DTBQ, ThymHQ/ThymBQ, and PhHQ/PhBQ. In general, the characteristic parameters of the DSSCs with the substituted derivatives surpassed those of the DSSC with the unsubstituted hydroquinone/benzoquinone electrolyte. The short-circuit current (J(sc)) of the devices using DTHQ/DTBQ and ThymHQ/ThymBQ (13.61 mA cm(-2) and 12.56 mA cm(-2), respectively) are comparable to the J(sc) obtained for cobalt(II/III) tris (bipyridine) as a reference electrolyte (14.54 mA cm(-2)). However, parameters such as open-circuit voltage (V-oc) and fill factor (FF) (547 mV and 0.48, respectively) are far from competitive. The best photovoltaic performance was obtained for the pair ThymHQ/ThymBQ using a triphenylamine (TPA)-based organic dye (LEG4) as sensitizer and a hybrid counter electrode with poly(3,4-ethylenedioxythiophene) (PEDOT) and graphene. These experimental conditions give under 1 sun (98%) the highest efficiency (eta = 3.19%); low-light intensities of 12.3% and 51.8% suns lead to efficiencies of 3.34% and 3.29%, respectively. Electrochemical impedance spectroscopy (EIS) revealed that the main cause for loss in photocurrent is the low recombination resistance compared to Co(II/III) as reference electrolyte. Based on the EIS analysis, a down-shift of the conduction band of TiO2 was found for all assembled devices containing the organic redox mediators, which explains the low V-oc values for these derivatives.
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40.
  • Frimane, Azeddine, et al. (författare)
  • Identifying small decentralized solar systems in aerial images using deep learning
  • 2023
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 262
  • Tidskriftsartikel (refereegranskat)abstract
    • Statistics on installed solar energy systems (SES) play a crucial role in the solar energy industry, providing valuable information for a wide range of stakeholders, such as policy makers, authorities, and financial evaluators. For example, grid operators rely on accurate data on photovoltaic penetration levels to ensure the quality and stability of the power supply. In this research, we present an automatic approach helping generate these statistics using deep learning and image processing techniques. Our proposed model is a machine learning approach that utilizes a specific architecture of convolutional neural networks (CNN) called the "U-net'' to detect SES from aerial images. We experimented different network settings to enhance the SES identification performance.In this study, the model was evaluated using two datasets from different locations, one from Sweden and one from Germany. Additionally, the model was trained and tested on a combination of both datasets. The impact of image resolution was also examined. The experimental results show that this architecture performs better than many recent CNN models that have been proposed in the literature for the task of SES identification from aerial images. To make it easy for others to replicate our findings, We have shared all the scripts, software, and dependencies required for running the model in this paper, along with instructions on how to use it in Appendix A.
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41.
  • Frimane, Âzeddine, 1990-, et al. (författare)
  • Infinite hidden Markov model for short-term solar irradiance forecasting
  • 2022
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 244, s. 331-342
  • Tidskriftsartikel (refereegranskat)abstract
    • Hidden state models are among the most widely used and efficient schemes for solar irradiance modeling in general and forecasting in particular. However, the complexity of such models – in terms of the number of states – is usually needed to be specified a priori. For solar irradiance data this assumption is very difficult to justify.In this paper, an infinite hidden Markov model (InfHMM) is introduced for short-term probabilistic forecasting of solar irradiance, where the assumption of fixed number of states a priori is relaxed and model complexity is determined during the model training. InfHMM is a non-parametric Bayesian model (NPB) indexed with an infinite dimensional parameter space which allows the automatic adaptation of the model to the “correct” complexity. This facilitates the automatic adaptation of the model to all weather conditions and locations. Posterior inference for InfHMM is performed using the Markov chain Monte Carlo algorithm, namely the beam sampler.Data from 13 different sources are used to validate the proposed model and subsequently it is compared to two well-established models in the literature: Markov-chain mixture distribution (MCM) and complete-history persistence ensemble (CH-PeEn) models. Important results are found, that cannot be derived from the existing finite models, such as the variation of the number of states within and across sites. The comparison of the models shows that the InfHMM is more consistent in term of the forecasting horizon.For reproducibility of the methodology presented in this paper, we have provided an R script for the InfHMM as supplementary material.
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42.
  • Gallardo-Saavedra, Sara, et al. (författare)
  • Simulation, validation and analysis of shading effects on a PV system
  • 2018
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 170, s. 828-839
  • Tidskriftsartikel (refereegranskat)abstract
    • A simulation program for calculating the IV-curve for series connected PV-modules during partial shadowing has been developed and experimentally validated. The software used for modelling the modules is LTspice IV. The validation has been done by means of a comparative analysis using the experimental results obtained in a set of tests performed on the mono-crystalline modules of the Gävle University's laboratory in Sweden. Experimental measurements were carried out in two groups. The first group is a string of six modules with bypass diodes while the second one corresponds to a single PV module. The simulation results of both groups demonstrated a remarkable agreement with the experimental data, which means that the designed model can be used for simulating the influence of shading on the power of a string. The model has been used for analysing the performance of strings of PV modules with shadows and the benefits of installing DC-DC optimizers or module inverters, that minimise the impact of shading, have been investigated.
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43.
  • Garrido, Jorge, et al. (författare)
  • Experimental and numerical performance analyses of a Dish-Stirling cavity receiver : Geometry and operating temperature studies
  • 2018
  • Ingår i: Solar Energy. - : Pergamon Press. - 0038-092X .- 1471-1257. ; 170, s. 913-923
  • Tidskriftsartikel (refereegranskat)abstract
    • Higher performance cavity receivers are needed to increase the competitiveness of solar power plants. However, the design process needs to be improved with more relevant experimental and numerical analyses. Thereby, the performance of four different Dish-Stirling cavities is investigated experimentally analyzing the influence of the cavity aperture diameter and shape at various operating temperatures. Temperatures inside the cavity receiver were collected together with the electrical power produced by the engine-generator. Then, a thermal system simulation was modelled and a comprehensive multi-parameter and multi-operation validation was performed. To improve this validation, the temperature distribution across the receiver tubes was analyzed in order to relate temperatures on the irradiated region with the non-irradiated one, where thermocouples can measure. The simulations were later used to obtain cavity receiver efficiencies, temperatures and loss breakdowns. The results show that the cavity receiver must be studied in optimization processes in conjunction with the other system components. Moreover, the reverse-conical cavity was found to be more efficient than a nearly cylindrical shape. Regarding the cavity receiver thermal losses, radiation and natural convection present similar contributions in the system under study. Finally, it was found that thermocouples installed on a non-irradiated region can be used to obtain peak receiver temperatures if the measurements are rectified by a correction value proportional to the DNI.
  •  
44.
  • Guccione, Salvatore, et al. (författare)
  • Techno-economic optimisation of a sodium-chloride salt heat exchanger for concentrating solar power applications
  • 2022
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 239, s. 252-267
  • Tidskriftsartikel (refereegranskat)abstract
    • To enhance the economic viability of Concentrating solar power (CSP) plant, recent efforts have been directed towards employing high-temperature working fluid in the receiver and incorporating higher-efficiency power cycles. This work presents a techno-economic analysis of a sodium-chloride salt heat exchanger included in a sodium-driven CSP system with a supercritical CO2 power block. A quasi-steady state heat exchanger model was developed based on the TEMA guidelines, with the possibility of being customised in terms of media adopted, constraints, boundary conditions, and heat transfer correlations. The sodium-salt heat exchanger has been designed aiming at minimising the Levelized Cost of Electricity (LCOE) of the plant. The performance and the design of the proposed heat exchanger have been evaluated via multi-objective optimisation and sensitivity analyses. Results show that advanced CSP systems employing sodium and an indirect chloride salt storage can represent an economically viable solution and can drive towards the future goal of 5 USD/MWh. For a base-case 100 MWe plant with 12 h of storage, a LCOE of 72.7 USD/MWh and a capacity factor (CF) higher than 60% were reached. The techno-economic investigations showed the potential LCOE reduction of 6% as well as the flexibility and robustness of the heat exchanger model. The developed tool lays the groundwork to explore potential improvements of this new generation of CSP systems.
  •  
45.
  • Haller, M., et al. (författare)
  • A method to determine stratification efficiency of thermal energy storage processes independently from storage heat losses
  • 2010
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 84:6, s. 997-1007
  • Tidskriftsartikel (refereegranskat)abstract
    • A new method for the calculation of a stratification efficiency of thermal energy storages based on the second law of thermodynamics is presented. The biasing influence of heat losses is studied theoretically and experimentally. Theoretically, it does not make a difference if the stratification efficiency is calculated based on entropy balances or based on exergy balances. In practice, however, exergy balances are less affected by measurement uncertainties, whereas entropy balances can not be recommended if measurement uncertainties are not corrected in a way that the energy balance of the storage process is in agreement with the first law of thermodynamics. A comparison of the stratification efficiencies obtained from experimental results of charging, standby, and discharging processes gives meaningful insights into the different mixing behaviors of a storage tank that is charged and discharged directly, and a tank-in-tank system whose outer tank is charged and the inner tank is discharged thereafter. The new method has a great potential for the comparison of the stratification efficiencies of thermal energy storages and storage components such as stratifying devices.
  •  
46.
  • Hesaraki, Arefeh, 1987-, et al. (författare)
  • Low-temperature Heat Emission Combined with Seasonal Thermal Storage and Heat Pump
  • 2015
  • Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 119, s. 122-133
  • Tidskriftsartikel (refereegranskat)abstract
    • We studied the application of a stratified seasonal hot water storage tank with a heat pump connected to medium-, low- and very-low-temperature space heat emissions for a single-family house in Stockholm, Sweden. Our aim was to investigate the influence of heat emission design temperature on the efficiency and design parameters of seasonal storage in terms of collector area, the ratio of storage volume to collector area (RVA), and the ratio of height to diameter of storage tank. For this purpose, we developed a mathematical model in MATLAB to predict hourly heat demand in the building, heat loss from the storage tank, solar collector heat production, and heat support by heat pump as a backup system when needed. In total, 108 cases were simulated with RVAs that ranged from 2 to 5 (m3 m−2), collector areas of 30, 40, and 50 (m2), height-to-diameter-of-storage-tank ratios of 1.0, 1.5, and 2.0 (m m−1), and various heat emissions with design supply/return temperatures of 35/30 as very-low-, 45/35 as low-, and 55/45 (°C) as medium-temperature heat emission. In order to find the best combination based on heat emission, we considered the efficiency of the system in terms of the heat pump work considering coefficient of performance (COP) of the heat pump and solar fraction. Our results showed that, for all types of heat emission a storage-volume-to-collector area ratio of 5 m3 m−2, with a collector area of 50 m2, and a height-to-diameter ratio of 1.0 m m−1 were needed in order to provide the maximum efficiency. Results indicated that for very-low-temperature heat emission the heat pump work was less than half of that of the medium-temperature heat emission. This was due to 7% higher solar fraction and 14% higher COP of heat pump connected to very-low-temperature heat emission compared to medium-temperature heat emission.
  •  
47.
  • Imani, Roghayeh, et al. (författare)
  • Modelling iodine diffusion in 2D-Perovskites as a function of the length of the organic spacer molecules
  • 2024
  • Ingår i: Solar Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-092X .- 1471-1257. ; 272
  • Tidskriftsartikel (refereegranskat)abstract
    • Two-dimensional (2D) hybrid perovskites have emerged as promising materials for solar cell applications, offering increased stability and reduced ionic movements compared to the more commonly used 3D-perovskites. The atomistic mechanisms behind the lower ionic diffusion in these perovskites have remained rather underexplored. In this study, we have used density functional theory (DFT) to investigate the potential tunability of ionic movements in 2D-perovskites by varying the spacer molecules in the structure. We demonstrate that by changing the length of the spacer molecule, and thus the distance between the two-dimensional inorganic slabs of corner sharing lead halide octahedra, it is possible to significantly modulate the periodic potential distribution and long-range electrostatic interactions within these materials. This modulation has a distinct impact on the energy barriers for ionic movement. Notably, we find that longer spacer molecules decrease the energy barrier for in-plane iodine diffusion, while increasing the energy barrier for inter-layer diffusion. Furthermore, we observe a logarithmic relationship between the energy barrier for inter-layer diffusion and the inter-layer distance. These results clarify the mechanisms underlying the lower ionic movement in 2D-perovskites and open avenues for engineering ionic migration in novel 2D-perovskite structures, thus enhancing their applicability in optoelectronic technologies.
  •  
48.
  •  
49.
  • Jacobsson, T. Jesper, 1984-, et al. (författare)
  • 2-Terminal CIGS-perovskite tandem cells : A layer by layer exploration
  • 2020
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 207, s. 270-288
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper focuses on the development of 2-terminal CIGS-perovskite tandem solar cells by exploring a range of stack sequences and synthetic procedures for depositing the associated layers. In the end, we converged at a stack sequence composed of SLG/Mo/CIGS/CdS/i-ZnO/ZnO:Al/NiO/PTAA/Perovskite/LiF/PCBM/SnO2/ITO. With this architecture, we reached performances only about 1% lower than the corresponding 4-terminal tandem cells, thus demonstrating functional interconnects between the two sub-cells while grown monolithically on top of each other. We go through the stack, layer-by-layer, discussing their deposition and the results, from which we can conclude what works, what does not work, and what potentially could work after additional modifications. The challenges for a successful 2-terminal tandem device include: how to deal with, or decrease, the surface roughness of the CIGS-stack, how to obtain uniform coverage of the layers between the CIGS and the perovskite while also obtaining a benign interface chemistry, and how to tune the band gaps of both the CIGS and the perovskite to obtain good optical matching. The investigation was based on CIGS with a power conversion efficiency around 14%, and perovskites with an efficiency around 12%, resulting in 2-terminal tandem cells with efficiencies of 15–16%. The results indicate that by using higher performing CIGS and perovskite sub-cells, it should be possible to manufacture highly efficient 2-terminal CIGS-perovskite tandem devices by using the protocols, principles, and procedures developed and discussed in this paper.
  •  
50.
  • Jonsson, Andreas, 1977-, et al. (författare)
  • Evaluation of control strategies for different smart window combinations using computer simulations
  • 2010
  • Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 84:1, s. 1-9
  • Tidskriftsartikel (refereegranskat)abstract
    • Several studies have shown that the use of switchable windows could lower the energy consumption of buildings. Since the main function of windows is to provide daylight and visual contact with the external world, high visible transmittance is needed. From an energy perspective it is always best to have the windows in their low-transparent state whenever there are cooling needs, but this is generally not preferable from a daylight and visual contact point of view. Therefore a control system, which can be based on user presence, is needed in connection with switchable windows. In this study the heating and cooling needs of the building, using different control mechanisms were evaluated. This was done for different locations and for different combinations of switchable windows, using electrochromic glazing in combination with either low-e or solar control glazing. Four control mechanisms were investigated; one that only optimizes the window to lower the need for heating and cooling, one that assumes that the office is in use during the daytime, one based on user presence and one limiting the perpendicular component of the incident solar irradiation to avoid glare and too strong daylight. The control mechanisms were compared using computer simulations. A simplified approach based on the balance temperature concept was used instead of performing complete building simulations. The results show that an occupancy-based control system is clearly beneficial and also that the best way to combine the panes in the switchable window differs depending on the balance temperature of the building and on the climate. It is also shown that it can be beneficial to have different window combinations for different orientations.
  •  
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