Evaluation of a New Tool for Heliostat Field Flux Mapping

A method for calculating the irradiance distribution on a receiver or target is further evaluated in this paper. The method, called PHLUX (Photographic Flux) mapping, uses a CCD camera to determine the irradiance distribution using recorded images of the illuminated receiver or target. The only information that is required is the direct normal irradiance, the receiver reflectivity, the subtended source angle of the sun (~9.3 mrad), and the pixel values of the receiver and sun images. Additional sensors, flux gauges, calorimeters, or scaling factors are not required. The novel feature of this method is that an image of the sun is used to scale both the magnitude and subtended angle of each pixel. This paper describes tests to evaluate the impact of camera settings (shutter speed, aperture, and filters) on the CCD response. Additional tests are performed that demonstrate that the FLUX method is independent of distance and angle between the camera and target, and that the method can be applied to non-planar (tubular) surfaces.