Solar-absorbers of Ni-NiO is evaluated with a method where the effective refractive index has been analysed to determine the steepness in the transition from low reflectance in the solar wavelength range to high in infrared.
Optical constants for simulations were obtained by R- and T-measurements on TiAlN thin films deposited on Corning 7059 glass. The model parameterized free carrier effects and an inter-band excitation. The calculations demonstrated that the colour effects are due to interference and inter-band absorption around 500 nm in a single layer coating. The peak shifts with the thickness of the thin film which gives a simple way to obtain different colours. Solar absorptance of 86 % can be reached already for a single TiAlN-film on an Al substrate.
Angular dependence of coloured absorber coatingsShuxi Zhao1, Dechun Zhu2 and Carl-G.Ribbing1 1) Div. of Solid State Physics, Angstrom Laboratory, Uppsala University Box 534, SE-751 21 Uppsala, Sweden2) Dept. of Chemical and Materials Engineering, Hefei University 230022, Hefei, PR. China AbstractInvestigations of angular dependence of thermal solar absorber coatings have been carried out in the Uppsala SSP-division since more than 10 years. In this contribution the angular variation of the optical properties of the recently suggested TiAlN-based coloured absorber is reported. The presence of an interference controlled colour raises a concern that strong irradiscence might make the roof integration of such absorbers aesthetically unsuitable. Using colour coordinates calculated from the measured reflectance spectra we reach the conclusion that the attractive colour seen in normal incidence is only marginally changed by the natural change of angle of incidence for a stationary collector. A second issue to be considered is whether this new absorber surface performs better or worse than earlier cermet absorbers when the solar incidence angle varies. The reflectance of TiAlN, as well as the antireflected TiAlON, as a function of wavelength and angle of incidence has therefore been measured using an integrating sphere with a rotatable sample holder in the centre. For comparison and calibration such measurements, such measurement was also carried out on a freshly sputtered, opaque gold film. The angular variation was fitted using the Incident Angle Modifier Kta, the ratio of the measured absorptance for incidence angle, to that at normal incidence:AbstractInvestigations of angular dependence of thermal solar absorber coatings have been carried out in the Uppsala SSP-division since more than 10 years. In this contribution the angular variation of the optical properties of the recently suggested TiAlN-based coloured absorber is reported. The presence of an interference controlled colour raises a concern that strong irradiscence might make the roof integration of such absorbers aesthetically unsuitable. Using colour coordinates calculated from the measured reflectance spectra we reach the conclusion that the attractive colour seen in normal incidence is only marginally changed by the natural change of angle of incidence for a stationary collector.
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