At IGTE, there is the possibility to optically characterize materials. For this purpose, an UV-VIS-NIR (ultraviolet-visible-infrared) double-beam spectrometer is available which allows measurements of spectral reflection, transmission and absorption in a wavelength range of 170 up to 3,300 nm with a resolution of 1 nm.
In the field of solar thermal applications, the measurement of the diffuse reflectance or transmittance is usually relevant. Therefore, the spectrometer is equipped with an integrating sphere (also called Ulbricht sphere). Thus, the desired parameters in a wavelength range of 250 up to 2,500 nm can be determined in compliance with the relevant standard specifications.
The performance of thermal solar collectors is significantly influenced by the optical properties of the materials used. The absorptivity of the absorbers and the transmittance of transparent coverings are crucial.
The determination of the optical properties of solar collector components is described in the ISO/DIN 22975-3 standard. Among other things, the requirements are specified for the measuring system; and the procedure is described for determining the solar absorptance of absorbers or the solar transmittance of transparent covers.