Mg-Ti-H thin films as switchable solar absorbers

The reflection and transmission spectra of Pd capped MgyTi1??y thin films (y ¼ 0:7; 0:8 and 0.9) are measured in the 0.5–5.5 eV energy range, both in the as-prepared and hydrogenated states. Upon hydrogenation these films switch reversibly from a shiny metallic state into a ‘‘black’’ absorbing one. The composition and thicknesses can be tailored to achieve high solar absorptance and low thermal emittance in the hydrogenated state. The combination of these two characteristics is interesting for the application of this material as switchable absorber in solar collectors. The use of a MgyTi1??y switchable absorber in solar collectors allows to lower the stagnation temperature from 180 to 80 1C. The collector efficiency is affected only minimally.