Advanced Solar Absorber Coatings Based on Nanocomposites

The design of an efficient and stable solar selective coating for photo-thermal conversion plants requires a complex study of the materials that composed the coating. The optimal optical properties for those absorber coatings are high solar absorptance in the wavelength range of 0.3 to 2.5 μm which corresponds to solar spectrum under atmospheric conditions and low thermal emittance in the infrared wavelength range.
Carbon-transition metal nanocomposites have been selected as absorber materials because they show appropriate optical properties as well as thermal and mechanical stability at high temperatures. The refractory metal carbide nanoparticles have been experimentally shown to stabilize the surrounding carbon matrix at least up to 700°C.
The computer simulation program CODE has been used to calculate solar absorptance and thermal emittance of various multilayers coatings material combinations of carbon - metal nanocomposites (NCTM). The optical properties of the inhomogeneous composite material were simulated with a physical model proposed by Bruggeman and Maxwell Garnett which average the dielectric function of the components of the composite. This allows treating the composite system as an effective medium.
This contribution compares simulated optical properties for different nanocomposite structural configurations (layer thickness, metal to carbon ratio). The calculated results are in the range of 0.91-0.97 for solar absorptance and 0.02 - 0.07 for thermal emittance at 300K.