Heliostat tracking based on circumsolar radiance maps

Abstract

A system and method for tracking the sun with a heliostat mirror is disclosed. The solar tracking system comprises: a camera configured to capture high dynamic range images of the sky, a plurality of cameras configured to capture images of the heliostat mirror, and a tracking controller. The images of the heliostat mirror include reflections of the sky. The tracking controller is configured to generate a circumsolar radiance map characterizing the brightness of at least a portion of the sky with the high dynamic range images. During tracking operations, the tracking controller is configured to estimate an orientation of the heliostat mirror; calculate coordinates of the portions of sky in the reflections in the heliostat mirror; estimate brightness levels of portions of sky in the reflections of the heliostat mirror based on the calculated coordinates and the radiance model; determine brightness levels of portions of sky in the reflections of the heliostat mirror based on the images from the plurality of cameras; generate an error measurement characterizing a difference between the brightness level estimated from the radiance model and the brightness level determined from the images of the heliostat mirror; search for an orientation angle of the at least one mirror that minimizes the error measurement; and re-orient the at least one mirror based on the orientation angle that minimizes the error measurement.