Session: 05-12 Heliostat Consortium 2

Paper Number: 113406

113406 - Extending Deflectometry Metrology Capability for Concentrating Solar Power 

Concentrating Solar Power (CSP) mirrors require high optical accuracy to be economically and technically viable for commercial CSP plants. CSP optics can have errors in the optical surface, the relative pointing of individual facets in a multi-facet array, and the absolute pointing of the optic to the receiver. It is important to be able to measure these errors both in a factory setting where the mirrors are first fabricated, as well as in the field where the mirrors are deployed. Deflectometry is a measurement technique that can measure the optical quality of large mirrors and has historically been used to measure CSP mirrors [1, 2]. Deflectometry systems can measure the surface quality of individual CSP heliostat facets [1, 2] and the relative pointing of facets in a multi-facet array [3]. Deflectometry systems for CSP have also been demonstrated indoors as well as outdoors in situ [1, 2].

Sandia’s deflectometry tool, SOFAST, existed for many years after its creation as a research tool used indoors to measure single CSP facets.  Since then, we have made improvements to the system, continuing to make it a more useful tool for industry spanning the development phases of prototype design, factory production, and use outdoors in operational CSP facilities.  

In this presentation we will briefly review the SOFAST system and describe several improvements and novel capabilities that make it more powerful, accessible, and applicable to a wider range of problems.  Basic improvements include the ability to simultaneously measure high-resolution slope maps and relative canting directions of facets in multi-facet arrays, higher code quality meeting modern software engineering standards, comprehensive documentation, and easier setup and operation.

In addition to these basic improvements, we will present key new capabilities that improve the program’s utility, range of applicability, and ease of use.  These include decoupling data acquisition, data processing, and data visualization into separate processes, built-in ray tracing analysis to produce predictions of sun-disc images based on measured mirror surface data, photogrammetric projector and screen surface calibration, an interactive SolidWorks CAD tool to aid layout design, and new ways to verify the accuracy of deflectometry measurements by comparing against ground truth references.

These improvements have enabled the SOFAST CSP deflectometry system to solve a range of problems that were previously out of reach.  We will present example measurement results across a range of use cases spanning prototype development to full heliostat measurement in situ.    Examples will include a benchtop demonstration using a laptop webcam, an indoor laboratory setup used to rapidly measure single CSP facets, and an outdoor setup capable of measuring multiple full heliostats in an operational solar field.  

These improvements make SOFAST a more useful tool to industry. The tool is overall easier to use, there is more useful functionality, and we are building trust in SOFAST measurement accuracy. As we continue our improvements, SOFAST will continue to transition from a tool used for research to a tool that can be easily used by industry.

References

[1] C. Andraka, S. Sadlon, B. Myer, K. Trapeznijov, and C. Liebner. Rapid Reflective Facet Characterization Using Fringe Reflection Techniques.  Journal of Solar Energy Engineering 136, February 2014.

[2] Steffen Ulmer, Tobias März, Christoph Prahl, Wolfgang Reinalter, Boris Belhomme. Automated high resolution measurement of heliostat slope errors. Solar Energy 85, pp. 685-687, 2011.

 [3] Charles E. Andraka and Julius E. Yellowhair. AIMFAST for Heliostats: Canting Tool for Long Focal Lengths. AIP Conference Proceedings 2126, 2019.

Presenting Author: Randy Brost Sandia National Laboratories

Presenting Author Biography: Dr. Randy Brost is a technical staff member at Sandia National Laboratories in the Concentrating Solar Power Technology group. He currently leads projects related to concentrating solar optics. He received his Ph.D. in Computer Science from Carnegie-Mellon University in 1991, and performed robotics research at Sandia National Laboratories until 1997. He then served at Eastman Kodak Company until 2007, implementing a variety of custom software tools supporting advanced manufacturing, metrology, and physics analysis. He then joined SkyFuel, a concentrating solar power company, where he helped develop the SkyTrough, a utility-scale parabolic trough collector, and applied computational methods to optimize new solar collector designs. He returned to Sandia in 2011, and pursued a variety of computer science research topics before joining the Concentrating Solar Technology group in early 2020.