Ultra-Accelerated Weathering System: Restoration, Optical Characterization, and Validation

The restoration of the Ultra-Accelerated Weathering System (UAWS) at the National Renewable Energy Laboratory (NREL) is a strategic step forward in U.S. technological infrastructure, increasing the potential for workforce development and domestic manufacturing. The UAWS is an experimental apparatus developed to expose samples to highly concentrated ultraviolet (UV) radiation from reflected natural sunlight. As one of just three UAWS installations in use globally, this system enhances America's leadership in advanced materials testing and development by facilitating the accelerated outdoor assessment of cutting-edge technologies in the defense, aerospace, automotive, and innovative energy industries. The UAWS system uses a rectangular arrangement of 370mm square spherical mirror facets mounted on a tracking structure. These facets have a specialized UV-reflective coating to deliver a homogeneous concentrated UV flux over a 150mm square target plane at the intersection of the facets' reflections. The original system used 29 facets to achieve a concentration ratio of 100:1 at the target plane, but was recently damaged by a severe hailstorm. The solar tracking system was repaired, and a new pyrheliometer was installed to ensure that the solar tracking kept the system aligned during unmanned operation. Extensive optical characterization work was performed to re-characterize the remaining 20 of the original 29 reflective facets, and the new effective UV concentration ratio was determined to be 65.8 at the sample area. This guarantees quick and precise testing procedures that shorten product development cycles, enhances quality assurance procedures, and reduces manufacturing cost. The direct normal UV flux was measured concurrently at NREL's co-located Solar Radiation Research Laboratory (SRRL) and used to produce calculations of the total UV radiation delivered to the sample area, with uncertainty bounds. In addition, standardized samples of polystyrene were irradiated on the UAWS to measure their degradation and test whether even flux was being delivered across the sample area, despite the missing facets. The results confirm that there were no significant differences in the weathering of the samples relative to their placement on the UAWS. America's larger strategy for industrial resilience and technological leadership is supported by this infrastructure investment, especially in areas that are essential to future economic growth and energy independence.