The Development of Direct Absorption and Storage Media for Falling Particle Solar Central Receivers
Spherical sintered bauxite particles between 200 mu m and 700 mu 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 (alpha(s)) greater than 0.90, which gradually degrades with extended heating in air at 700 degrees C and above. The degradation mechanism is an oxidation reaction that can be reversed via thermal or chemical reduction, resulting in alpha(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.