Comparison of Two Sun Tracking Methods in the Application of a Heliostat Field

[+] Author and Article Information
Y. T. Chen

Institute of Energy and Environment, Malaysia University of Science and Technology, C901, Kelana Square, No. 17, Jln SS7/26, Kelana Jaya, 47301 Petaling Jaya, Selangor, Malaysiaemail: ytchen@must.edu.my

A. Kribus

Dept. of Fluid Mechanics and Heat Transfer, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel   email: kribus@yarkon.eng.tau.ac.il

B. H. Lim, C. S. Lim, K. K. Chong

Institute of Energy and Environment, Malaysia University of Science and Technology, C901, Kelana Square, No. 17, Jln SS7/26, Kelana Jaya, 47301 Petaling Jaya, Selangor, Malaysia  

J. Karni

Environmental Science and Energy Research Department, Weizmann Institute of Science, Rehovot 76100, Israel   email: Jacob.karni@weizmann.ac.il

R. Buck, A. Pfahl

Institute of Technical Thermodynamics, German Aerospace Center (DLR), Pfaffenwaldring 38-40, Stuttgart 70569, Germany

T. P. Bligh

Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdomemail: tpb@eng.cam.ac.uk

J. Sol. Energy Eng 126(1), 638-644 (Feb 12, 2004) (7 pages) doi:10.1115/1.1634583 History: Received January 01, 2003; Revised April 01, 2003; Online February 12, 2004
Copyright © 2004 by ASME
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Spot size comparison between the spinning-elevation and azimuth-elevation tracking methods for June 21st. The target angle is 41.8 deg, facing angle is 10 deg to the south and the latitude is North 43 deg. Heliostat area is 25 m2 and the slant range is 30 m.
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The schematic diagram shows the difference between the two kinds of sun tracking methods: (a) azimuth-elevation; (b) spinning-elevation.
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The definitions of geometric parameters used in the comparison of heliostats
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The layout shows the heliostat field used for comparison between the two types of heliostat design. The dimensions shown are in meters. The tower height is 20 m. The specifications for each heliostat are given in Table 1.
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The comparison of image spread for heliostat 7 at different times on June 21. The dimensions shown are in centimeters. Each point represents the intersection on the target plane of a central ray from an individual facet. Left side: traditional heliostat; right side: non-imaging focusing heliostat. (a) 7 am. (b) 9 am. (c) 11 am. (d) 1 pm. (e) 3 pm.
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The characteristic curves for heliostat 7 at different times during June 21. (a) Traditional heliostat. (b) Non-imaging focusing heliostat.
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The yearly maximum spillage loss is shown as a function of the receiver diameter. Upper curve: traditional heliostat. Lower curve: new heliostat.
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The flow chart of smoothing process
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The smoothing procedure is demonstrated for heliostats 3, 4, 5 and 6 during Nov. 21 (a) Presetting time for all four heliostats are the same i.e. 2 pm, 21st Jan. (b) The presetting time for each heliostat is optimized to produce a relatively uniform distribution during daily operation.
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The best and worst characteristic curves for both sun-tracking methods are plotted. The characteristic curves for all other times are within the two limits.
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The time variation of spillage loss for the entire field diameter is plotted for both sun-tracking methods during June 21. (a) Receiver aperture diameter is 1 m. (b) Aperture diameter 1.2 m. (c) Aperture diameter 1.4 m.




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