Reflective mirror facets for concentrating solar power (CSP) systems have stringent requirements on the surface slope accuracy in order to provide adequate system performance. This paper presents a tool that can fully characterize facets quickly enough for 100% inspection on a production line. A facet for a CSP system, specifically a dish concentrator has a parabolic design shape. This shape will concentrate near-parallel rays from the sun to a point (or a line for trough systems). Deviations of surface slope from the design shape impact the performance of the system, either losing power that misses the target or increasing peak fluxes to undesirable levels. During development or production, accurate knowledge of facet defects can lead to improvements to lower cost or improve performance. The reported characterization system, SOFAST (Sandia Optical Fringe Analysis Slope Tool), has a computer-connected camera that images the reflective surface, which is positioned so that it reflects an active target, such as an LCD screen, to the camera. A series of fringe patterns are displayed on the screen while images are captured. Using the captured information, the reflected target location of each pixel of mirror viewed can be determined, and thus through a mathematical transformation, a surface normal map can be developed. This is then fitted to the selected model equation, and the errors from design are characterized. While similar approaches have been explored, several key developments are presented here. The combination of the display, capture, and data reduction in one system allows rapid characterization. An “electronic boresight” approach is utilized to accommodate physical equipment positioning deviations, making the system insensitive to setup errors. Up to 1.5 × 106 points are characterized on each facet. Finally, while prior automotive industry commercial systems resolve the data to shape determination, SOFAST concentrates on slope characterization and reporting, which is tailored to solar applications. SOFAST can be used for facet analysis during development. However, the real payoff is in production, where complete analysis is performed in about 10 s. With optimized coding, this could be further reduced.

References

References
1.
Liden
,
R.
,
2007
, “
Solar Dish Stirling Systems Report
,” NREL CSP Technology Workshop, Denver, CO, Mar.
2.
U.S. Department of Energy, Energy Efficiency and Renewable Energy
,
2003
, “
Solar Energy Technologies Program Multi-Year Technical Plan 2003-2007 and Beyond
,” U.S. Department of Energy, Washington, DC, Jan. 2004, DOE/GO-102004-1775.
3.
Andraka
,
C. E.
,
2008
, “
Cost/Performance Tradeoffs for Reflectors Used in Solar Concentrating Dish Systems
,”
ASME 2nd International Conference on Energy Sustainability (ES2008)
,
Jacksonville, FL
, August 10–14,
ASME
Paper No. ES2008-54048.10.1115/ES2008-54048
4.
Andraka
,
C. E.
,
Yellowhair
,
J.
, and
Iverson
,
B. D.
,
2010
, “
A Parametric Study of the Impact of Various Error Contributions on the Flux Distribution of a Solar Dish Concentrator
,” ASME 4th International Conference on Energy Sustainability, Phoenix, AZ, May 17–22,
ASME
Paper No. ES2010-90242, pp.
565
580
.10.1115/ES2010-90242
5.
Jones
,
S. A.
,
Neal
,
D. R.
,
Gruetzner
,
J. K.
,
Houser
,
R. M.
,
Edgar
,
R. M.
,
Kent
,
J.
, and
Wendelin
,
T. J.
,
1996
, “
VSHOT: A Tool for Characterizing Large, Imprecise Reflectors
,”
International Symposium on Optical Science Engineering and Instrumentation
,
Denver, CO
, August 4–9.
6.
Jones
,
S. A.
,
Gruetzner
,
J. K.
,
Houser
,
R. M.
,
Edgar
,
R. M.
, and
Wendelin
,
T. J.
,
1997
, “
VSHOT Measurement Uncertainty and Experimental Sensitivity Study
,”
IECEC-97: Proceedings of the Thirty-Second Intersociety Energy Conversion Engineering Conference, Honolulu, HI, July 27-August 1, Vol. 3, Energy Systems, Renewable Energy Resources, Environmental Impact and Policy Impacts on Energy, American Institute of Chemical Engineers
,
New York
, pp.
1877
1882
.
7.
Ulmer
,
S.
,
Heller
,
P.
, and
Reinalter
,
W.
,
2008
, “
Slope Measurements of Parabolic Dish Concentrators Using Color-Coded Targets
,”
ASME J. Sol. Energy Eng.
,
130
(
1
), p.
011015
.10.1115/1.2807193
8.
Marz
,
T.
,
Prahl
,
C.
,
Ulmer
,
S.
,
Wilbert
,
S.
, and
Weber
,
C.
, 2011, “
Validation of Two Optical Measurement Methods for the Qualification of the Shape Accuracy of Mirror Panels for Concentrating Solar Systems
,”
ASME J. Sol. Energy Eng.
,
133
(
3
), p.
031022
10.1115/1.4004240.
9.
Ulmer
,
S.
,
März
,
T.
,
Prahl
,
C.
,
Reinalter
,
W.
, and
Belhomme
,
B.
,
2011
,
Automated High Resolution Measurement of Heliostat Slope Errors
,”
Sol. Energy
,
85
(
4
), pp.
681
687
.10.1016/j.solener.2010.01.010
10.
CSP Services
,
2012
, “
Deflectometric Measurement System QDec
,” sales brochure, Cologne, Germany.
11.
Heimsath
,
A.
,
Platzer
,
W.
,
Bothe
,
T.
, and
Wansong
,
L.
,
2008
, “
Characterization of Optical Components for Linear Fresnel Collectors by Fringe Reflection Method
,”
Proceedings of SolarPACES Symposium
,
Las Vegas, NV
, March 4–7.
12.
The Engineer Source, 2007 “Sensors Automate Reflective Quality Control,” Engineering Talk website, Centaur Communications Ltd., London, accessed November 16, www.engineeringtalk.com/news/mip/mip140.html
13.
Li
,
W.
,
Bothe
,
T.
,
von Kopylow
,
C.
, and
Jüptner
,
W.
, 2004, “Evaluation Methods for Gradient Measurement Techniques,”
Proc. SPIE 5457: Optical Metrology in Production Engineering
, 300, (September 10, 2004), Strasbourg, France, April 27–30.10.1117/12.546002
14.
Agrawal
,
A.
,
Raskar
,
R.
, and
Chellappa
,
R.
,
2006
, “
What is the Range of Surface Reconstructions From a Gradient Field?
,”
Proceedings of the 9th European Conference Computer Vision (ECCV2006)
, Graz, Austria, May 7–13.
15.
Höfling
,
R.
,
Aswendt
,
P.
, and
Neugebauer
,
R.
,
2000
, “
Phase Reflection—A New Solution for the Detection of Shape Defects on Car Body Sheets
,”
Opt. Eng.
,
39
(
1
), pp.
175
182
.10.1117/1.602349
16.
Malacara, Daniel
,
1992
,
Optical Shop Testing
,
John Wiley & Sons, Inc.
,
New York
.
17.
Bothe
,
T.
,
Li
,
W.
,
von Kopylow
,
C.
, and
Jüptner
,
W.
,
2004
, “
High-Resolution 3D Shape Measurement on Specular Surfaces by Fringe Reflection
,”
Proc. SPIE 5457: Optical Metrology in Production Engineering
, 411 (September 10, 2004), Strasbourg, France, April 27–30.10.1117/12.545987
18.
Andraka
,
C. E.
,
Finch
,
N.
,
Yellowhair
,
J.
,
Francis
,
M.
,
Hunt
,
K.
, and
Kulaga
,
T.
,
2011
, “
SOFAST Facet Characterization for Heliostats: Extensions and Difficulties
,”
Proc. SolarPACES
2011, Granada, Spain, September 20–23.
19.
Burke
,
J.
,
Bothe
,
T.
,
Osten
,
W.
, and
Hess
,
C. F.
,
2002
, “
Reverse Engineering by Fringe Projection
,”
Proc. SPIE 4778
, Interferometry XI: Applications, 312 (June 19, 2002), Seattle, WA, July 10–11.10.1117/12.473547
20.
Saldner
,
H. O.
, and
Huntley
,
J. M.
,
1997
, “
Profilometry Using Temporal Phase Unwrapping and a Spatial Light Modulator-Based Fringe Projector
,”
Opt. Eng.
,
36
(
2
), pp.
610
615
.10.1117/1.601234
21.
Basler Vision Technologies
,
2007
, “
Basler A641f Camera Specification
,”
Document #BD000410
,
Basler Vision Technologies, Exton, PA
.
23.
Bouguet
,
J.-Y.
,
2008
, “
Camera Calibration Toolbox for Matlab
,”
http://
www.vision.caltech.edu/bouguetj/calib_doc/
24.
Disto Classic5 Hand-Held Laser Meter User Manual
, 2004, Lieca Geosystems AG, Switzerland.
25.
Diver
,
R. B.
, and
Andraka
,
C. E.
,
2003
, “
Integration of the Advanced Dish Development System
,”
Proceedings of the ASME International Solar Energy Conference
(
ISEC2003
),
Kohala Coast, HI
, March 15–18, ASME Paper No. ISEC2003-44238.10.1115/ISEC2003-44238
26.
Lopez
,
C. W.
, and
Stone
,
K. W.
,
1992
, “
Design and Performance of the Southern California Edison Stirling Dish
,” ASME-JSES-KSES International Solar Energy Conference, Maui HI, April 5–9, pp.
945
952
.
27.
Andraka
,
C. E.
, and
Powell
,
M. P.
,
2008
, “
Dish Stirling Development for Utility-Scale Commercialization
,”
14th Biennial CSP SolarPACES Symposium
,
Las Vegas NV
, March 4–7.
28.
Andraka
,
C. E.
,
Diver
,
R. B.
, and
Rawlinson
,
K. S.
,
2003
, “
Improved Alignment Technique for Dish Concentrators
,”
Proceedings of the ASME International Solar Energy Conference
(
ISEC2003
), Kohala Coast, HI, March 15–18, ASME Paper No. ISEC2003-44088.10.1115/ISEC2003-44088
29.
Finch
,
N. S.
,
Andraka
,
C. E.
,
2013
, “
Uncertainty Analysis and Characterization of the SOFAST Mirror Facet Characterization System
,” ASME 5th International Conference on Energy Sustainability (
ICES2011
), Washington, DC, August 7–10, ASME Paper No. ES2011-54455.10.1115/ES2011-54455
30.
Finch
,
N. S.
, and
Andraka
,
C. E.
,
2011
, “
Uncertainty Quantification of the SOFAST Mirror Facet Characterization System Using Probabilistic Modeling
,”
Proc. SolarPACES
2011, Granada, Spain, September 20–23.
31.
Romero
V. J.
,
1991
, “
CIRCE2/DEKGEN2: A Software Package for Facilitated Optical Analysis of 3-D Distributed Solar Energy Concentrators—Theory and User Manual
,” Sandia National Laboratories, Albuquerque, NM, SAND91-2238.
You do not currently have access to this content.