| 1. |
- Adeyefa, ZD, et al.
(författare)
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Spectral solar irradiance before and during a Harmattan dust spell
- 1996
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Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 57:3, s. 195-203
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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)
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Recent advances in electrochromics for smart windows applications
- 1998
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Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 63:4, s. 199-216
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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)
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Degradation mechanisms in a dye-sensitized solar cell studied by UV-VIS and IR spectroscopy
- 2003
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Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 75:2, s. 169-180
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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)
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High temperature solar heated seasonal storage system for low temperature heating of buildings
- 2000
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Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 69:6, s. 511-523
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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)
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Evaluation of CPC-collector designs for stand-alone, roof- or wall installation
- 2005
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 79:6, s. 638-647
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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)
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Measurement of radiation distribution on the absorber in an asymmetric CPC collector
- 2004
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 76:1-3, s. 199-206
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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)
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Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface
- 2000
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Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 68:4, s. 325-328
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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)
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Preliminary design and analysis of a novel solar receiver for a micro gas-turbine based solar dish system
- 2015
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 114:4, s. 378-396
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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)
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Stable and efficient PbS colloidal quantum dot solar cells incorporating low-temperature processed carbon paste counter electrodes
- 2017
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Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 158, s. 28-33
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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)
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Zirconium nitride based transparent heat mirror coatings : preparation and characterisation
- 1994
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 32:2, s. 199-212
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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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