Abstract
In a thermophotovoltaic (TPV) system, a heat source brings an emitter to incandescence and the spectrally confined thermal radiation is converted to electricity by a low-bandgap photovoltaic (PV) cell. Efficiency is dominated by the emitter's ratio of in-band emissivity (convertible by the PV cell) to out-of-band emissivity (inconvertible). Two-dimensional photonic crystals (PhCs) offer high in-band emissivity and low out-of-band emissivity at normal incidence, but have reduced in-band emissivity off-normal. According to Lambert's law, most thermal radiation occurs off-normal. An omnidirectional PhC capable of high in-band emissivity at all angles would increase total in-band power by 55% at 1200°C. In this work, we present the first experimental demonstration an omnidirectional hafnia-filled 2D tantalum PhC emitter suitable for TPV applications such as combustion, radioisotope, and solar TPV. Dielectric filling improved the hemispherical performance without sacrificing stability or ease of fabrication. The numerical simulations, fabrication processes, and optical and thermal characterizations of the PhC are presented in this paper.
Highlights
Our 2D metallic photonic crystal meets all of the requirements of a selective emitter for high-temperature energy conversion
The performance of our conformally coated photonic crystal has been consistently good at normal incidence [9, 10], most of the thermal radiation occurs off-normal according to Lambert’s law
While metamaterial designs based on metal-dielectric stacks [11] and 2D metallic pyramid arrays [12] have shown promise, they are difficult to fabricate and have not been experimentally demonstrated at high temperatures under extended operation
Summary
- Photonic Crystal Emitters for Thermophotovoltaic Energy Conversion Veronika Stelmakh, Walker R Chan, Michael Ghebrebrhan et al. - Photonic Crystal Enabled Thermophotovoltaics for a Portable Microgenerator Walker R Chan, Veronika Stelmakh, Christopher M Waits et al. - Energy shift experiment in photonic crystal medium A A Akhmadeev, R Kh Gainutdinov, G Hermann et al
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