Spectral characterization of specular reflectance of solar mirrors

•A new instrument for spectral measurements of specular reflectance was designed.•It permits to measure spectral specular reflectance at different acceptance angles.•The precision of the system is in the range of ±0.1 percentage points.•The solar weighted specular reflectance of four typical reflectors has been measured.•The measured data points have been fitted applying a specular reflectance model.

Solar reflectors for concentrating solar power (CSP) concentrators require a high specular reflectance over the whole solar spectrum. A preliminary procedure to measure the reflectance of solar mirror materials has been proposed in the SolarPaces reflectance measurement guideline [1]. However, the guideline clearly states that the currently available measurement instruments need further improvement in order to be able to fully characterize the reflectance properties of solar reflectors. In this work a high precision spectral reflectometer has been developed that permits the measurement of the solar weighted specular reflectance at different incidence and acceptance angles and thus provides all relevant reflectance data of solar mirrors. Four typical reflector materials have been measured and the solar weighted reflectance as a function of the acceptance angle has been modeled.