Development of cost efficient solar receiver tube with a novel tandem absorber system

New single layer, double layer and triple layer absorber tandems were designed and developed for high performance Organic Ranking Cycle (ORC) based solar thermal applications. A Cr-Mn-Fe composite oxide based absorber layer is devolved by controlled chemical oxidation and designed to have a nanoporous structure. It is covered with double antireflective layers a ZrO 2 -SiO 2 nanocomposite layer developed by the sol-gel route and a porous SiO 2 layer obtained from SiO 2 nanoparticle suspension. Double and triple layer tandem absorbers were developed by a combination of chemical, sol-gel and nanoparticle suspension methods. By varying process parameters like duration, temperature and withdrawal speed, different combinations of Cr-Mn-Fe oxides/ZrO 2 -SiO 2 double layer tandem and Cr-Mn-Fe oxides/ZrO 2 -SiO 2 /SiO 2 triple layer tandem composite absorber layers with varying refractive indices were developed on an economical variety of SS substrate. The optimized thickness of the absorber layer along with the antireflective layers shown a high absorptance (α = 94.9) and low warm emittance (e = 0.122 at 300 °C). More specifically, this novel double layer tandem coating has excellent optical properties along with high corrosion resistance (withstands > 200 h in salt spray test). It has good thermal stability in an open air atmosphere and is well suited for low and medium temperature solar thermal applications.