Uncertainty Study of Reflectance Measurements for Concentrating Solar Reflectors

Abstract

The solar reflector is one of the main components of concentrated solar thermal systems. Therefore, accurate knowledge of its solar-weighted, near-specular reflectance is highly important. Currently, this parameter cannot be properly measured with a single commercial instrument. There is a great interest in having a suitable procedure that can guarantee the accuracy of reflector quality analysis, which already led to the publication of an international measurement guideline (title "Parameters and method to evaluate reflectance properties of reflector materials for concentrating solar power technology"). Still, more research work is needed to improve the state of the art. At present, both the specular reflectance and the spectral hemispherical reflectance are measured by using commercial portable reflectometers and spectrophotometers, respectively, to gain enough information. This article concentrates on the evaluation and calculation of the type-B (nonstatistical) uncertainties associated with these employed instruments and, therefore, leads to a more accurate definition of the measurement uncertainty. Considering type-B uncertainty, the expanded uncertainties of measurements for most of the reflector types are U B,ref = 0.006 for monochromatic specular reflectance and U B,spec = 0.016 for solar-weighted hemispherical reflectance.

UV degradation of primary mirrors in outdoor exposure and accelerated aging

“…Periodically, both the samples exposed outdoors and tested under accelerated aging conditions were collected and analyzed in the laboratory. Spectral hemispherical reflectance, ,h ([ a , b ], i ,h), at =[320, 2500] nm and i =8º, was measured with a spectrophotometer model Lambda 1050 manufactured by Perkin Elmer (and an integrating sphere of 150 mm diameter) to observe the wavelength regions affected for the UV dose [6]. To properly appreciate the reflectance degradation in the same scale, the hemispherical reflectance drop in the whole spectrum was calculated.…”