Highly-Efficient Selective Metamaterial Absorber for High-Temperature Solar Thermal Energy Harvesting

TL;DR

This paper presents a nanostructured metamaterial solar absorber with high broadband solar absorption, low IR emittance, and thermal stability up to 350°C, significantly improving solar thermal energy harvesting efficiency.

Contribution

The work introduces a novel metamaterial design with nanostructured titanium gratings that achieves high solar absorption and low IR emittance, demonstrating experimental validation and high-temperature stability.

Findings

Absorber achieves >90% absorption in UV, visible, and near IR

Mid-IR emittance is approximately 20%

Predicted solar-to-heat efficiency up to 80% at 400°C

Abstract

In this work, a metamaterial selective solar absorber made of nanostructured titanium gratings deposited on an ultrathin MgF2 spacer and a tungsten ground film is proposed and experimentally demonstrated. Normal absorptance of the fabricated solar absorber is characterized to be higher than 90% in the UV, visible and, near infrared (IR) regime, while the mid-IR emittance is around 20%. The high broadband absorption in the solar spectrum is realized by the excitation of surface plasmon and magnetic polariton resonances, while the low mid-IR emittance is due to the highly reflective nature of the metallic components. Further directional and polarized reflectance measurements show wide-angle and polarization-insensitive high absorption within solar spectrum. Temperature-dependent spectroscopic characterization indicates that the optical properties barely change at elevated temperatures up to 350{\deg}C. The solar-to-heat conversion efficiency with the fabricated metamaterial solar absorber is predicted to be 78% at 100{\deg}C without optical concentration or 80% at 400{\deg}C with 25 suns, and could be further improved with better fabrication processes and geometric optimization during metamaterial design. The strong spectral selectivity, favorable diffuse-like behavior, and excellent thermal stability make the metamaterial selective absorber promising for significantly enhancing solar thermal energy harvesting in various system at mid to high temperatures.