Enhanced Thermal Stability of W‐Ni‐Al₂O₃ Cermet‐Based Spectrally Selective Solar Absorbers with Tungsten Infrared Reflectors

Abstract

Solar thermal technologies such as solar hot water and concentrated solar power trough systems rely on spectrally-selective solar absorbers. These solar absorbers are designed to efficiently absorb the sunlight while suppressing re-emission of infrared radiation at elevated temperatures. Efforts for the development of such solar absorbers must not only be devoted to their spectral selectivity but also to their thermal stability for high temperature applications. In this work selective solar absorbers based on two cermet layers are fabricated using a magnetron sputtering technique on mechanically 2 polished stainless steel substrates. The targeted operating temperature is 500 -600 °C. However, we observed a detrimental change in the morphology, phase, and optical properties if the cermet layers are deposited on a stainless steel substrate with a thin nickel adhesion layer, which is due to the diffusion of iron atoms from the stainless steel into the cermet layer forming a FeWO 4 phase. In order to improve thermal stability and reduce the infrared emittance, we find tungsten to be a good candidate for the infrared reflector layer due to its excellent thermal stability and low infrared emittance. We demonstrate a stable solar absorptance of ~0.90 and total hemispherical emittance of 0.15 at 500 °C.

Concentrating solar thermoelectric generators with a peak efficiency of 7.4%

“…4). 41 The solar absorber has a temperature-independent solar absorptance of approximately 0.91 and measured infrared total hemispherical emittance of ~0.15 at 500 °C which can be extrapolated to ~0.18 at 600 °C. The high-temperature reference paint HE6 by Rolls Royce is applied on a stainless steel substrate and used as the black paint solar absorber with a temperature-independent solar absorptance and total-hemispherical emittance of 0.95…”

“…9 At high optical solar concentration STEGs are fabricated with a solar absorber based on a spectrally-selective double cermet multilayer stack. 41 The STEG for high optical concentration is also fabricated with a reference black paint (HE6) as solar absorber surface ( Supplementary Fig. 7).…”

“…Another possible explanation is absorber damage since at ~250 kW m -2 , the absorber operating temperature is above 600 o C (Fig.2d) while the double-cermet absorber was only proven to be stable in vacuum up to 600 °C. 41 Overall, however, the gain in efficiency by using a spectrally-selective solar absorber instead of black paint at such high optical solar concentration is not substantial and might not justify the increased complexity in the STEG fabrication. STEGs optimized for high optical solar concentration, it is still a remarkable improvement over previous reports in the literature (Fig.…”

Large‐Scale Nanophotonic Solar Selective Absorbers for High‐Efficiency Solar Thermal Energy Conversion

“…Although various combinations of host ceramics such as Al 2 O 3 , AlN, and SiO 2 with metal particle fi llers including Ni, Co, Mo, W, Au, Ag, etc., have been extensively investigated in terms of spectral performance and thermal stability, it is still quite diffi cult to develop high-performance cermet-based absorbers stable at >700 °C. [ 8,9 ] Nanophotonic structures, e.g., 1D, 2D, and 3D photonic crystals, have been explored for use as solar selective absorbers, but these structures are far from meeting the goal of ≈100% absorptance for the broadband solar spectrum. [10][11][12][13][14] Moreover, these nanophotonic structures are fabricated through high-cost and complex processes, such as reactive ion etching (RIE), atomic layer deposition (ALD), chemical mechanical planarization (CMP), and cannot be easily scaled up.…”

Toward a High‐Efficient Utilization of Solar Radiation by Quad‐Band Solar Spectral Splitting

“…[13,14] Cermet based spectral-selective absorbers are integrated in the quad-band splitter owing to their high solar absorptance, low IR emittance as well as good thermal stability for mid-and hightemperature applications. [14] There are many kinds of selective solar-thermal absorbers with different configurations, such as intrinsically selective semiconductor-metal coatings, textured surfaces, multi-layer metal-composites (cermets), and selectively-transmitting coatings on [14,15] can demonstrate a solar absorptance of 0.90~0.96.…”