Development of a low environmental impact, porous solar absorber coating utilizing binary/ternary solvent blends for CSP systems

Abstract

Concentrated solar power utilizes a field of mirrors to redirect solar rays onto a central receiver to generate thermal energy through heat transfer media and a Rankine steam cycle. To effectively transfer heat to the heat transfer material, the receiver has to efficiently convert/absorb the incoming solar flux without losing energy to radiation. Receivers are coated with a solar absorber coating evaluated with a figure of merit which weighs the energy absorbed by the sample against the total incident energy. The structure of the painted coating plays a large part in the long-term stability and optical properties of the solar absorber coatings. We investigated the effects of different solvents on the micro-structure of black oxide coated paint tiles and evaluated the stability of the paint colloid using the Gibbs free energy of mixing. We also investigated the use of low environmental impact solvents as potential alternates to standard solvents to create low-stress films. The results show that paint blends thinned by blends of dimethyl carbonate and tertbutylbenzene have low-stress surface morphology with pore-like structures due to the favorable Gibbs free energy value of the colloid and reduced evaporation rate of the primary solvents. These coatings also exhibited strong optical performance with figure of merit and solar absorbance values of 91.60% and 96.86%, making them ideal coatings for next generation concentrated solar power plants.