The Development of Direct Absorption and Storage Media for Falling Particle Solar Central Receivers

Spherical sintered bauxite particles between 200  μ m and 700  μ m in diameter have been shown to be effective in the direct absorption and storage of concentrated solar energy. These particles are commercially available in large quantities and exhibit as-received solar weighted absorptance ( α s) greater than 0.90, which gradually degrades with extended heating in air at 700 °C and above. The degradation mechanism is an oxidation reaction that can be reversed via thermal or chemical reduction, resulting in α s > 0.95 along with enhanced resistance to further degradation for some formulations. Certain metal oxide pigments, added to Al2O3:SiO2, have proven to achieve solar weighted absorptance levels similar to those of the commercially available particles and may be promising alternatives to currently available materials.