0
Research Papers

Compensation of Gravity Induced Heliostat Deflections for Improved Optical Performance

[+] Author and Article Information
James K. Yuan

Sandia National Laboratories,
Concentrating Solar Technologies Department,
P.O. Box 5800,
Albuquerque, NM 87185-0828
e-mail: jkyuan@sandia.gov

Joshua M. Christian

Sandia National Laboratories,
Concentrating Solar Technologies Department,
P.O. Box 5800,
Albuquerque, NM 87185-1127
e-mail: jmchris@sandia.gov

Clifford K. Ho

Sandia National Laboratories,
Concentrating Solar Technologies Department,
P.O. Box 5800,
Albuquerque, NM 87185-1127
e-mail: ckho@sandia.gov

1Under contract to Sandia National Laboratories.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received February 13, 2013; final manuscript received October 21, 2014; published online November 17, 2014. Assoc. Editor: Markus Eck.

The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Sol. Energy Eng 137(2), 021016 (Apr 01, 2015) (8 pages) Paper No: SOL-13-1054; doi: 10.1115/1.4028938 History: Received February 13, 2013; Revised October 21, 2014; Online November 17, 2014

Heliostat optical performance can be affected by both wind and gravity induced deflections in the mirror support structure. These effects can result in decreased energy collection efficiency, depending on the magnitude of structural deflections, heliostat orientation and field position, and sun position. This paper presents a coupled modeling approach to evaluate the effects of gravity loading on heliostat optical performance, considering two heliostat designs: The National Solar Thermal Test Facility (NSTTF) heliostat and the Advanced Thermal Systems (ATS) heliostat. Deflections under gravitational loading were determined using finite element analysis (FEA) in Ansys Mechanical, and the resulting deformed heliostat geometry was analyzed using Breault Apex optical engineering software to evaluate changes in beam size and shape. Optical results were validated against images of actual beams produced by each respective heliostat, measured using the Beam Characterization System (BCS) at Sandia National Laboratories. Simulated structural deflections in both heliostats were found to have visible impacts on beam shape, with small but quantifiable changes in beam power distribution. In this paper, the combined FEA and optical analysis method is described and validated, as well as a method for modeling heliostats subjected to gravitational deflection and canted in-field, for which mirror positions may not be known rigorously. Furthermore, a modified, generalized construction method is proposed and analyzed for the ATS heliostat, which was found to give consistent improvements in beam shape and up to a 4.1% increase in annual incident power weighted intercept (AIPWI).

Copyright © 2015 by ASME
Your Session has timed out. Please sign back in to continue.

References

Moya, A. C., and Ho, C. K., 2011, “Modeling and Validation of Heliostat Deformation due to Static Loading,” ASME Paper No. ES2011-54216. [CrossRef]
Duffie, J. A., and Beckman, W. A., 2006, Solar Engineering of Thermal Processes, 3rd ed., Wiley, Hoboken, NJ, p. 908.
Strachan, J. W., and Houser, R. M., 1993, “Testing and Evaluation of Large Area Heliostats for Solar Thermal Applications,” Sandia National Laboratories, Report No. SAND92-1381UC.
Winter, C. J., Sizmann, R. L., and Vant-Hull, L. L., 1991, Solar Power Plants: Fundamentals—Technology—Systems—Economics, Springer-Verlag, Berlin, Germany.
National Solar Radiation Data Base, 2005, “Typical Meteorological Year 3,” National Renewable Energy Laboratory, http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/
Buck, R., and Teufel, E., 2007, “Comparison and Optimization of Heliostat Canting Methods,” ASME Paper No. ES2007-36168. [CrossRef]

Figures

Grahic Jump Location
Fig. 1

Representative heliostat designs. NSTTF heliostat (left) and ATS heliostat (right)

Grahic Jump Location
Fig. 2

NSTTF (left) and ATS (right) heliostat models in Ansys Mechanical

Grahic Jump Location
Fig. 3

Schematic of modeling procedure for heliostat canted to counter gravitational deflection. Left: the canting orientation, with adjustment acceleration aligned with gravity, zero deflection. Right: rotated heliostat with adjustment acceleration not aligned with gravity and net acceleration and deflection.

Grahic Jump Location
Fig. 4

Optical model in Breault APEX, consisting of a sun source, the heliostat geometry, and a target

Grahic Jump Location
Fig. 5

Simulated NSTTF beam images from undeformed and gravity deformed heliostat models during equinox. Plot window dimensions are 7 m × 7 m.

Grahic Jump Location
Fig. 6

Simulated NSTTF beam images from gravity deformed and undeformed heliostat models for various times of day during summer solstice. Plot window dimensions are 7 m × 7 m.

Grahic Jump Location
Fig. 7

Simulated NSTTF beam images from gravity deformed and undeformed heliostat models for various times of day during winter solstice. Plot window dimensions are 7 m × 7 m.

Grahic Jump Location
Fig. 8

BCS beam images versus simulated beams from NSTTF Heliostat, Day 194, NSTTF Site, Albuquerque, NM

Grahic Jump Location
Fig. 9

Simulated ATS beam images from gravity deformed and undeformed heliostat models for various times of day during equinox. Plot window dimensions (h × w) are 9.0 m × 10.5 m.

Grahic Jump Location
Fig. 10

Simulated ATS beam images from gravity deformed and undeformed heliostat models for various times of day during summer solstice. Plot window dimensions (h × w) are 9.0 m × 10.5 m.

Grahic Jump Location
Fig. 11

Simulated ATS beam images from gravity deformed and undeformed heliostat models for various times of day during winter solstice. Plot window dimensions (h × w) are 9.0 m × 10.5 m.

Grahic Jump Location
Fig. 12

Simulated ATS beams versus contour plots of BCS beams, day 238, NSTTF Site, Albuquerque, NM (plot window dimensions 9.0 × 10.5 m)

Grahic Jump Location
Fig. 13

Heliostat deformed configurations when adjusted for no deflection at a single elevation angle. Left: “Clam-shelling” at elevation angles below the adjustment angle. Right: sagging of structure at elevation angles above the adjustment angle. Deflections scaled ∼500×.

Grahic Jump Location
Fig. 14

Intercept factors on a target two times the minimum theoretical beam size (∼4.4 m), for various modeled ATS heliostat configurations during equinox

Grahic Jump Location
Fig. 15

Intercept factors on a target two times the minimum theoretical beam size (∼4.4 m), for various modeled ATS heliostat configurations during summer solstice

Grahic Jump Location
Fig. 16

Intercept factors on a target two times the minimum theoretical beam size (∼4.4 m), for various ATS heliostat configurations during winter solstice

Grahic Jump Location
Fig. 17

Daily and annual power weighted intercept factors on a target two times the minimum beam size (∼4.4 m) for various modeled ATS heliostat configurations

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In