Abstract
SummaryThis work experimentally studies a silicon-cored tungsten nanowire selective metamaterial absorber to enhance solar-thermal energy harvesting. After conformally coating a thin tungsten layer about 40 nm thick, the metamaterial absorber exhibits almost the same total solar absorptance of 0.85 as the bare silicon nanowire stamp but with greatly reduced total emittance down to 0.18 for suppressing the infrared emission heat loss. The silicon-cored tungsten nanowire absorber achieves an experimental solar-thermal efficiency of 41% at 203°C during the laboratory-scale test with a stagnation temperature of 273°C under 6.3 suns. Without parasitic radiative losses from side and bottom surfaces, it is projected to reach 74% efficiency at the same temperature of 203°C with a stagnation temperature of 430°C for practical application, greatly outperforming the silicon nanowire and black absorbers. The results would facilitate the development of metamaterial selective absorbers at low cost for highly efficient solar-thermal energy systems.
Highlights
Within the last decade, nanostructured metamaterials have become an attractive topic in the field of radiative heat transfer for thermal energy harvesting (Bello and Shanmugan, 2020; Jin et al, 2016; Khodasevych et al, 2015; Woolf et al, 2018; Xu et al, 2020) and radiative cooling (Raman et al, 2014; Zhai et al, 2017)
Simpler and more costeffective methods are still in need for large-area manufacturing of selective metamaterial solar absorbers. All these experimentally demonstrated metamaterial solar absorbers are achieved via typical periodicity and feature size around a few hundred nanometers, which can be feasibly fabricated with deep UV projection or stepper photolithography (Enrico et al, 2019; Greiner et al, 2006; Park and Lee, 2016)
We present the simple fabrication, optical characterization, and laboratory-scale solar-thermal tests of a selective metamaterial solar absorber made of silicon-cored WNWs to experimentally demonstrate the improved performance in converting solar energy to heat under multiple solar concentrations due to its excellent spectral selectivity
Summary
Within the last decade, nanostructured metamaterials have become an attractive topic in the field of radiative heat transfer for thermal energy harvesting (Bello and Shanmugan, 2020; Jin et al, 2016; Khodasevych et al, 2015; Woolf et al, 2018; Xu et al, 2020) and radiative cooling (Raman et al, 2014; Zhai et al, 2017). For harvesting solar energy to heat, spectrally selective absorbers with high solar absorption and low infrared emission are highly desired for efficient energy conversion, and many metamaterial selective solar absorbers have been designed and experimentally demonstrated recently based on multilayer (Chirumamilla et al, 2016, 2019; Dyachenko et al, 2016; Khoza et al, 2019; Thomas et al, 2017; Wang et al, 2018), periodic tungsten convex or concave gratings (Jae Lee et al, 2014; Wang et al, 2015; Wang and Wang, 2013), nickel nanopyramids and tungsten nanowires (WNWs)/doughnuts (Behera and Joseph, 2017; Li et al, 2015; Tian et al, 2018), and nanoporous or nanoparticle composite structures (Lu et al, 2016, 2017; Prasad et al, 2018) Due to their submicron feature sizes, advanced fabrication techniques such as electron-beam lithography and focused-ion beam were usually needed for fabricating these metamaterial structures (Wang et al, 2015), which are expensive with low throughput prohibiting their large-area application. Diffraction gratings for optical devices and nanoimprinting stamps, made of nanopatterned silicon wafers fabricated by deep UV projection lithography along with selective chemical or plasma etching (Opachich et al, 2015; Sanjay et al, 2014), have been commercialized in large area with controllable shape and geometries (Lightsmyth, n.d.)
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