Optimal design of irradiance redistribution guides for the National Renewable Energy Laboratory's high-flux solar furnace

The National Renewable Energy Laboratory (NREL) has developed and operates the high-flux solar furnace (HFSF), a 10-kW solar concentrator used for research in solar energy applications. An application of ongoing interest is the heat-bonding of metallic foils to ceramic substrates, a process requiring a highly uniform irradiance distribution over a 10 by 10-cm target area, as well as a mean irradiance of at least 10 W/cm2, and a working distance of at least 10-cm from the optics. Science Applications International Corporation (SAIC) and NREL have developed designs for two reflective irradiance redistribtuion guides (IRGs) for use in conjunction with the HFSF, which provide significantly enhanced irradiance uniformity while exceeding the mean-irradiance and working-distance requirements. Irradiance- uniformity levels of 7.2% and 3.1% root-mean-square (RMS) deviation over the target area were achieved by the two IRG designs. The designs were generated using SAICs nonimaging concentrator synthesis code, which employs a global optimization procedure. The HFSF was modeled by means of an optical ray set produced by NREL's solar furnace code. The IRG designs are novel in that they feature re-entrant optics combined with the intentional use of ray paths having different nubmers of multiple reflections within a single reflective optical component in order to achieve the desired irradiance distribution.