CATARACT - Computer Code for Improving Power Calculations at NREL's High-Flux Solar Furnace

The High-Flux Solar Furnace (EIFSF), operated by the National Renewable Energy Laboratory, uses a camera-based, flux-mapping system to analyze the flux distribution and to determine total power at the focal point. The flux-mapping system consists of a diffusely reflecting plate with seven circular foil calorimeters, a charge-coupled device (CCD) camera, an IBM-compatible personal computer with aframe-grabber board, and commercial image analysis software. The calorimeters provide flux readings that are used to scale the image captured from the plate by the camera. The image analysis software can estimate total power incident on the plate by integrating under the 3-dimensional image. Because of the physical layout of the HFSF, the camera is positioned at a 20 degree angle to the fluxmapping plate normal. The foreshortening of the captured images that results represents a systematic error in the power calculations because the software incorrectly assumes the image is parallel to the camera's array. We have written a FORTRAN computer program called CATARACT (Camera/TARget Angle CorrecTion) that we use to transform the original flux-mapper image to a plane that is normal tothe camera's optical axis. A description of the code and the results of experiments performed to verify it are presented. Also presented are comparisons of the total power available from the HFSF as determined from the flux mapping system and theoretical considerations.