Static screen deflectometry for twisting heliostat metrology

This paper describes a heliostat metrology system in which the reflector shape is obtained from measurements of the reflected screen pattern with a fine-scale scalable regular pattern. The reflection of the screen across the heliostat is viewed by a distant camera focusing on the heliostat. This method is especially valuable for setting and testing the different shapes of a reflector whose shape is to be changed through the day, according to the changing of sun’s altitude and incidence angle. Such changing shape is valuable for use in concentrating solar-thermal power (CSP) systems targeting high concentration and temperature. The developed method is named static screen deflectometry (SSD). It has been tested in a heliostat with a single sheet float glass reflector measuring 2.4 𝑚×3.3 𝑚 and bent into different shapes to focus a disc image of the sun at a 113 𝑚 distance target, throughout a day. A static screen measuring 2.4 𝑚×4.3 𝑚 was assembled from perforated steel sheet with ¾ inch holes on a 1” inch staggered grid. The screen is placed at 12.5 𝑚 from the heliostat, and its reflection by the heliostat is recorded by a camera at 50𝑚 distance. Data acquisition and processing algorithm has been developed to reconstruct the reflector surface shape from the camera images. From measurements of the heliostat reflector surface bent to multiple different astigmatic shapes, we determined the high measurement accuracy for surface slope to be 0.1 𝑚𝑟𝑎𝑑 with 25 𝑚𝑚 spatial resolution.. Authors: Huang, Yiyang [Univ. of Arizona, Tucson, AZ (United States); University of Arizona] (ORCID:0000000217416649); Angel, Roger [University of Arizona, Steward Observatory] (ORCID:0009000040668126); Kang, Hyukmo [Univ. of Arizona, Tucson, AZ (United States). College of Optical Sciences]; Choi, Heejoo [Univ. of Arizona, Tucson, AZ (United States). College of Optical Sciences]; Rademacher, Matthew [University of Arizona (United States) Steward Observatory] (ORCID:0009000272839721). DOE Contract: EE0010246. Subjects: 14 SOLAR ENERGY; reflector metrology, heliostat test, deflectometry, concentrating solar power