Development of a multi-camera metrology system for closed-loop heliostat control

Abstract

We present a six-camera optical metrology method for measuring heliostat misalignment from the decenter of reflected solar images at a receiver as a first step toward in-situ heliostat pose and shape control. We use three opposing camera pairs to measure differential irradiance and convert these measurements into the direction and magnitude of image decenter. We implement the method in the laboratory using a spherical concave mirror to represent a heliostat and controlled light source models to represent the Sun. We geometrically register the six camera images and apply Black/White normalization and radiometric response calibration to enable quantitative irradiance comparison among the cameras. For both Gaussian and solar limb-darkened light sources, the calculated misalignment follows the prescribed displacement in direction and magnitude. Pixel-resolved measurements also reveal spatial variations across the mirror aperture. These results demonstrate that a six-camera system can quantitatively sense heliostat misalignment through reflected solar image decenter and contain information for future surface correction and closed-loop heliostat surface control.