Spectral selectivity of high-temperature solar absorbers

Area of Science:

• Materials Science
• Optical Engineering
• Thermodynamics

Background:

• Selective solar absorbers are crucial for high-temperature energy conversion.
• Understanding the optical properties of absorber materials at elevated temperatures is essential for efficient design.

Purpose of the Study:

• To numerically calculate the thermal emissivity and normal incidence solar absorptivity of model spectrally selective solar absorbers at high temperatures.
• To investigate the effect of material composition and structure on absorber performance.

Main Methods:

• Numerical calculations were performed on model absorbers comprising Drude metal substrates coated with various dielectric and selectively absorbing layers.
• The study systematically varied layer composition, refractive index, and thickness, including graded refractive index profiles.
• Thermal emissivity (TH) and solar absorptivity (alpha(s)) were calculated as functions of temperature and layer properties.

Main Results:

• Coating metal substrates with dielectric layers increased thermal emissivity.
• Selective absorber layers with optimized spectral absorptivity resulted in high solar absorptivity and low thermal emissivity.
• Graded refractive index films showed marginal improvements in solar absorptivity and thermal emissivity compared to homogeneous films of similar thickness.

Conclusions:

• The optical properties of spectrally selective solar absorbers are highly dependent on material composition and structure.
• Graded refractive index designs offer minor performance enhancements for practical absorber applications at high temperatures.
• Further research may be needed to optimize graded absorber designs for significant performance gains.