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Solar Thermal Collectors at High Latitudes: Design and performance of non-tracking concentrators
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solar thermal collectors at high latitudes have been studied, with emphasis on concentrating collectors. A novel design of concentrating collector, the Maximum Reflector Collector (MaReCo), especially designed for high latitudes, has been investigated optically and thermally. The MaReCo is an asymmetrical compound parabolic concentrator with a bi-facial absorber. The collector can be adapted to various installation conditions, for example stand-alone, roof- or wall mounted. MaReCo prototypes have been built and outdoor-tested. The evaluation showed that all types work as expected and that the highest annually delivered energy output, 340 kWh/m2, is found for the roof MaReCo. A study of the heat-losses from the stand-alone MaReCo lead to the conclusion that teflon transparent insulation should be placed around the absorber, which decreases the U-value by about 30%.

A method was developed to theoretically study the projected radiation distribution incident on the MaReCo bi-facial absorber. The study showed that the geometry of the collectors could be improved by slight changes in the acceptance intervals. It also indicated that the MaReCo design concept could be used also at mid-European latitudes if the geometry is changed.

A novel method was used to perform outdoor measurements of the distribution of concentrated light on the absorber and then to calculate the annually collected zero-loss energy, Ea,corr, together with the annual optical efficiency factor. A study using this method indicated that the absorber should be mounted along the 20º optical axis instead of along the 65º optical axis, which leads to an increase of about 20% in Ea,corr. The same absorber mounting is suggested from heat loss measurements. The Ea,corr at 20º absorber mounting angle can be increased by 5% if the absorber fin thickness is changed from 0.5 to 1 mm and by 13% if two 71.5 mm wide fins are used instead of one that is 143 mm wide. If the Ea,corr for the standard stand-alone MaReCo with 143 mm wide absorber mounted at 65º is compared to that of a collector with a 71.5 mm wide absorber mounted at 20º, the theoretical increase is 38%.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2002. , p. 78
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 697
Keyword [en]
Materials science, Solar thermal collectors, concentrators, CPC, high latitudes
Keyword [sv]
Materialvetenskap, Solfångare, koncentratorer, höga latituder
National Category
Materials Engineering
Research subject
Solid State Physics
Identifiers
URN: urn:nbn:se:uu:diva-1925ISBN: 91-554-5274-4 (print)OAI: oai:DiVA.org:uu-1925DiVA, id: diva2:161491
Public defence
2002-04-29, Polhemssalen, Uppsala, 10:15 (English)
Opponent
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2009-04-29Bibliographically approved
List of papers
1. Evaluation of CPC-collector designs for stand-alone, roof- or wall installation
Open this publication in new window or tab >>Evaluation of CPC-collector designs for stand-alone, roof- or wall installation
2005 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 79, no 6, p. 638-647Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89748 (URN)10.1016/j.solener.2005.04.023 (DOI)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2017-12-14Bibliographically approved
2. Calorimetric measurements of heat losses from a truncated asymmetric solar thermal concentrator
Open this publication in new window or tab >>Calorimetric measurements of heat losses from a truncated asymmetric solar thermal concentrator
2002 (English)In: Solar EnergyArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-89749 (URN)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2009-04-29Bibliographically approved
3. Annually projected solar radiation distribution analysis for optimum design of asymmetric CPC
Open this publication in new window or tab >>Annually projected solar radiation distribution analysis for optimum design of asymmetric CPC
2002 (English)In: Solar EnergyArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-89750 (URN)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2009-04-29Bibliographically approved
4. Measurement of radiation distribution on the absorber in an asymmetric CPC collector
Open this publication in new window or tab >>Measurement of radiation distribution on the absorber in an asymmetric CPC collector
2004 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 76, no 1-3, p. 199-206Article in journal (Refereed) Published
Abstract [en]

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 UL-values.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-89751 (URN)10.1016/j.solener.2003.08.024 (DOI)
Conference
Solar World Congress 2001
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2017-12-14Bibliographically approved
5. Comparison of the optical efficiency of a wide and a narrow absorber fin in an asymmetric concentrating collector
Open this publication in new window or tab >>Comparison of the optical efficiency of a wide and a narrow absorber fin in an asymmetric concentrating collector
(English)Manuscript (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:uu:diva-89752 (URN)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2010-01-14Bibliographically approved
6. The influence of climate and location on collector performance
Open this publication in new window or tab >>The influence of climate and location on collector performance
2002 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 25, no 4, p. 499-509Article in journal (Refereed) Published
Abstract [en]

The influence of annual climate variations on the performance of solar thermal collectors in the northern part of Europe has been investigated. The annual solar collector energy output has been calculated with the MINSUN simulation program using hourly, measured climatic data for the years 1983–98 for three cities situated in the south (Lund), central (Stockholm) and north (Luleå) of Sweden. A synthetic year created with the Meteonorm weather simulation program was also used in the simulations. Two solar thermal collectors were modelled: a flat plate solar collector and a tubular vacuum collector, both of commercial standard.

The thermal energy output is strongly correlated to the annual global irradiation at a horizontal surface. The annual average energy delivered from the flat plate collector was 337 kWh/m2 for Stockholm (337 for Lund and 298 for Luleå), and from the vacuum tube collector 668 kWh/m2 for Stockholm (675 for Lund and 631 for Luleå) at an operating temperature of T=50°C. Maximum deviations from the average value for this 16-year period are around 20% for the flat plate and 15% for the vacuum tube collector, at T=50°C.

The relation between global irradiation on a horizontal surface and the annually collected thermal energy at a constant operating temperature could be fitted to a linear equation: qu=aG(0°)+bT, where qu is the energy output from the collector, G(0°) the global irradiation at a horizontal surface, T the average temperature of the collector fluid, and a and b fitting parameters in a double linear regression analysis.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89753 (URN)10.1016/S0960-1481(01)00091-X, (DOI)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2017-12-14Bibliographically approved
7. Simulation of the influence of tilt and azimuth angles on the collector output of solar collectors at northern latitudes
Open this publication in new window or tab >>Simulation of the influence of tilt and azimuth angles on the collector output of solar collectors at northern latitudes
1999 (English)In: Proceedings North Sun conference 1999, Edmonton CanadaArticle in journal (Refereed) Accepted
Identifiers
urn:nbn:se:uu:diva-89754 (URN)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2009-04-29Bibliographically approved
8. The impact of optical and thermal properties on the performance of flat plate solar collectors
Open this publication in new window or tab >>The impact of optical and thermal properties on the performance of flat plate solar collectors
Show others...
2000 (English)In: Proceedings Eurosun 2000, Copenhagen, DenmarkArticle in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-89755 (URN)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2009-04-29Bibliographically approved
9. Optical scattering from rough aluminum surfaces
Open this publication in new window or tab >>Optical scattering from rough aluminum surfaces
Show others...
2001 (English)In: J. Applied Optics, Vol. 40, p. 2148-2158Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-89756 (URN)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2009-04-29Bibliographically approved
10. Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface
Open this publication in new window or tab >>Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface
2000 (English)In: Solar Energy, Vol. 68, p. 325-328Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-89757 (URN)
Available from: 2002-04-05 Created: 2002-04-05 Last updated: 2009-04-29Bibliographically approved

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