High-temperature "ion baseball" for enhancing concentrated solar power efficiency

Recent guidelines for the third generation of solar absorber coatings have shown an unavoidable necessity for low thermal emittance coatings for concentrated solar power tower technology to decrease the thermal loss at the absorber surface. By tuning the pigment spinel crystal structure, density or roughness of a coating, improved optical properties for the coating can be achieved. In this study, a high solar-radiation absorbing pigment CuMn1.5Fe0.5O4 was calcined with 3 wt % Al, Fe, Ni, Mo and Cr to study the optical property improvement of the absorber coating, which could increase the efficiency of concentrated solar power plants. The modified pigment particles were investigated and compared to the non-modified pigment by XRD, TEM and elemental mapping, which showed that the pigment was successfully doped with Fe, Ni, and Cr. In contrast, no spinel doping was observed when Al and Mo were used. The most likely final position of the migrating Cr atoms was determined by comparing the experimental IR spectrum of the Cr-doped spinel structure with the spectra of various structures calculated based on first principles density functional theory calculations. Furthermore, the prepared coatings were thermally aged for 1300 h at 800 degrees C in air, followed by repetitive optical measurements. Outstanding results were achieved for the aged coating, which was made from a Cr-doped black pigment. Its solar absorptance ( > 95%) and epsilon(T)/alpha(s) ratio (0.94) after 1300 h of thermal ageing were better than that of a standard paint (epsilon(T)/alpha(s) = 1). We estimated that it may be possible to save up to 300,000 (sic)/year on a fully operating concentrated solar power (CSP) plant by replacing the standard absorber paint with the Cr-doped pigment due to its better absorption efficiency.