Fabrication and characterization of multiscale, fractal textured solar selective coatings

Abstract

Photothermal conversion efficiency depends significantly on the selectivity of the thermal receiver surface through which a heat transfer fluid flows in a concentrated solar power system. This paper presents studies on novel multiscale, fractal textured solar selective coatings for solar thermal applications. The fractal surfaces are fabricated integrally on the substrate material using electrodeposition. The coatings are described in terms of fractal parameters that are uniquely determined from surface measurements, and the optical properties of the coatings are experimentally characterized in detail in terms of the fractal parameters. The effects of heat treatment on the optical properties of coatings over a range of fractal parameters are also described. The study is presented considering coatings on copper to demonstrate that fractal texturing of the surface provides a nearly three-fold performance improvement compared to coatings with no texturing or heat treatment. The findings equally apply to other materials used in higher temperature solar thermal applications.