Development and Characterization of a Color 2F Alignment Method for the Advanced Dish Development System

Dish/Stirling systems rely on accurate mirrors and alignment. Inaccuracies in alignment can lead to flux “hotspots” that can reduce performance and even damage the solar receiver. To improve the alignment process a procedure that can be used to align solar dish concentrator facets was developed on the second-generation (Mod 2) Advanced Dish Development System (ADDS) at Sandia National Laboratories in Albuquerque, NM. The previously used facet alignment method was based on the distant light source technique and required the dish to be pointed near the horizon while an observer located approximately 100 meters away views the image of a target and calls in adjustments to an aligner. At high sun elevation angles structural deflections inherent in any dish concentrator result in facet misalignments. To address these issues while allowing improved access to facet adjustments, an alignment technique that permits alignment at any elevation angle was developed and evaluated. This technique utilized a video camera and color target affixed on a lightweight tower at a distance near twice the dish focal length (2f) from the vertex of the dish, hence the name “color 2f”. The camera and target are centered on the optical axis of the concentrator. During the initial evaluation of the color 2f facet alignment procedure on the ADDS Mod 2 concentrator, no facet adjustments were made. Instead concentrator facet deflections were measured by taking and evaluating images of the dish reflecting the target while the dish was pointed at the horizon, 45 degrees elevation, and vertical. These images were compared to each other, to determine gravity induced pointing errors as the dish changes in elevation. Future implementations of the color 2f system could be used to align the system rather than simply diagnose it. The proposed approach has the potential to accurately align concentrators without large open land spaces, and to account for elevation-induced structural deflections. In this paper, the color 2f alignment technique is described along with the results from the gravity induced structural deflection study. Issues and recommendations for improvement of the 2f alignment system are also presented.