Improved Alignment Technique for Dish Concentrators

Parabolic dish concentrators have shown significant promise of generating competitive electric energy for grid and off-grid applications. The efficiency of a dish-electric system is strongly affected by the quality of the concentrator optics. Most parabolic systems consist of a number of facets mounted to a support structure in an approximate parabolic arrangement, where the individual facets have spherical or parabolic optical shapes. The individual facets must be accurately aligned because improper alignment can compromise performance or create hot spots that can reduce receiver life. A number of techniques have been used over the years to align concentrator facets. In the Advanced Dish Development System (ADDS) project, a color look-back alignment approach that accurately aligns facets (mirror panels) and in addition indicates quantitative information about the focal length was developed. Key factors influencing the alignment, some of which had very large effects on the quality of the alignment, were also identified. The influence of some of the key factors was characterized with a flux mapping system on the second-generation ADDS concentrator. Some of these factors also affect other alignment approaches. The approach was also successfully applied to two other concentrators with differing facet arrangements. Finally, we have extended the method to a 2-f approach that eliminates the need for a distant line-of-sight to the dish and permits alignment at near vertical dish attitudes. In this paper, we outline the color look-back alignment approach, discuss the key alignment factors and their effect on flux distribution, and discuss extensions to non-gore dishes. A companion paper discusses the 2-f color alignment approach in detail.