Solar thermal trapping at 1,000°C and above

Abstract

Common semi-transparent materials like quartz and water feature spectral optical properties characterized by low attenuation of visible radiation and strong absorption of infrared (IR) radiation emitted by hot surfaces. This leads to the thermal trap effect, exploitable in solar-concentrating applications to attain higher absorber temperatures and thermal efficiencies. Here, we demonstrate this effect at high temperatures with a quartz rod attached to an opaque absorber plate reaching 1,050°C when exposed to 135 suns of concentration, while the quartz front face remains at 450°C. A 3D heat transfer model, validated against the experimental data, is applied to determine the performance map of solar receivers exploiting thermal trapping. These are shown to achieve the target temperature with higher efficiency and/or needing a lower concentration than the reference unshielded absorber. Solar process heat at above 1,000°C can decarbonize key industrial applications such as cement manufacturing and metallurgical extraction.