Heliostat Canting and Focusing Methods: An Overview and Comparison

A central receiver power tower system consists of a field of heliostats that focus the sunlight onto the receiver on the tower. Heliostats typically consist of an array of mirror facets that track the sun throughout the day. To obtain the optimal concentrated solar flux on the receiver, the individual heliostat facets must be properly canted and focused. Several different methods have been used in the past for facet canting and focusing. These demonstrated methods and some new alignment concepts are under consideration for development and alignment of the 218 heliostats at the Sandia National Laboratories National Solar Thermal Test Facility in Albuquerque, NM. In this paper, we provide an overview and comparison of the different methods. The methods we consider are the gauge blocks, inclinometers, photogrammetry, fringe reflection, imaging with theoretical image overlays, laser beam projections, camera look-back, and target reflection methods. The advantages and disadvantages of each alignment method are identified based on several prescribed criteria for aligning the heliostats. Recommendations regarding the alignment method’s potential for efficiently and accurately aligning heliostat fields are provided.