Characterization of High Temperature Solar Thermal Selective Absorber Coatings at Operation Temperature

AbstractIn cooperation between the Physikalisch-Technische Bundesanstalt (PTB) and the SCHOTT Solar CSP GmbH (SCHOTT Solar) measurements have been carried out with the goal to assure, that the directional-hemispherical reflectance measurements, done as production control by SCHOTT Solar, lead to applicable results for calculating the emittance of absorber tubes for parabolic trough receivers at their operation temperatures above 350°C.A significant influence of the temperature on the directional spectral emittance could not be found. Due to the spectral characteristics of the emittance with a rising spectral emittance towards shorter wavelength the spectral integrated quantity: directional total emittance becomes larger with an increasing temperature due to the shift of the Planckcurve.Furthermore, the measurements of PTB confirmed the emittance values calculated from the reflection measurements and the directional-hemispherical reflectance measurements performed by SCHOTT