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X-ray diffraction (XRD) patterns of as-synthesized Co3O4 and CuCo2O4 nanoneedles. Asterisks indicate peaks from the Haynes 230 substrate.
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Solar absorber coatings have widely been investigated for solar-thermal technologies including concentrated solar power and solar thermochemistry. While various nanostructures such as nanowires and nanotubes have been commonly used for high solar absorptance owing to their potent light trapping effect, the high temperature stability of these nanost...
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Light-trapping nanostructures have been widely used for improving solar cells’ performance, but the higher surface recombination and poor electrode contact introduced need to be addressed. In this work, silicon nanostructures were synthesized via silver-catalyzed etching to texturize solar cells. Atomic-layer-deposited Al2O3 passivated the nanotext...
Citations
... Nanostructures have been widely investigated as means of improving CST coatings [10][11][12][13][14][15][16][17] . Current CST coatings have nanostructures that are generally produced by a curing process in which organic material is burnt, such as engineered polymer beads 18 or a binder as in Pyromark 2500® 19 (or "Pyromark"); the latter coating is considered to be the gold standard in CST. ...
Light trapping enhancement by nanostructures is ubiquitous in engineering applications, for example, in improving highly-efficient concentrating solar thermal (CST) technologies. However, most nano-engineered coatings and metasurfaces are not scalable to large surfaces ( > 100 m²) and are unstable at elevated temperatures ( > 850 °C), hindering their wide-spread adoption in CST. Here, we propose a scalable layer nano-architecture that can significantly enhance the solar absorption of an arbitrary material. Our electromagnetics modelling predicts that the absorptance of cutting-edge light-absorbers can be further enhanced by more than 70%, i.e. relative improvement towards blackbody absorption from a baseline value without the nano-architecture. Experimentally, the nano-architecture yields a solar absorber that is 35% optically closer to a blackbody, even after long-term (1000 h) high-temperature (900 °C) ageing in air. A stable solar absorptance of more than 97.88 ± 0.14% is achieved, to the best of our knowledge, the highest so far reported for these extreme ageing conditions. The scalability of the layer nano-architecture is further demonstrated with a drone-assisted deposition, paving the way towards a simple yet significant solar absorptance boosting and maintenance method for existing and newly developed CST absorbing materials.
... air, water, or oil). 11 The conversion of solar energy to heat energy is a potential sector of renewable energy generation 12 due to its highly distributed capabilities 13 to meet future energy demands if properly exploited. Various types of solar collectors are used nowadays, such as flat plate, evacuated tube, parabolic dish, and parabolic trough collector. ...
... 25 In this present study, the analysis is done for a single riser tube of a flat plate collector for simplicity. Several researchers 13,20,21,25 conducted numerical simulations of flat plate collectors assuming single riser tubes for this type of simplicity. Considering adiabatic and symmetric side walls, analyzing a single riser tube is sufficient for studying the collector's behavior. ...
... The PEC values of the collectors for cases 2, 3, 4, 5, and 6 with respect to case 1 were calculated and are listed in Table IV using Eq. (13). ...
To obtain improved thermal performance of flat plate solar collectors, the effect of square and rectangular riser tubes of a flat plate collector (FPC) were numerically investigated and compared with circular riser tube FPC in the present study. For this purpose, a three-dimensional numerical model for FPC collectors has been developed and simulated in CFD software ANSYS FLUENT. Transient thermal performance analysis is carried out to find out the optimum geometrical configuration of the FPC riser tube. The numerical results indicated that using the square-shaped riser tube in FPC improves the collector’s useful heat exchange rate as well as thermal efficiency as compared to the use of circular and rectangular riser tubes. There is a maximum 8.1% higher heat exchange rate of the collector with a square riser tube than a circular riser tube under the same operating conditions. The average efficiency of the collector with the circular tube is 65.95%, whereas the square tube has the highest efficiency of 70.44%. However, the pressure drops through the square and rectangular riser geometry are higher than the circular tube. By making a balance between enhanced heat exchange rate and increased pressure drop, the performance evaluation criterion was evaluated and the square-shaped riser tube having the highest value of 2.65 is better than the other configurations. The results clearly indicate that the collector’s performance is notably influenced by the shape of the riser tube, with a square shape yielding superior performance.
... This allows very high solar absorption [40], even in very thin materials, leading for instance to a price reduction of PV panels [41][42][43]. Some examples of these structures are gratings [44][45][46], cavity arrays [47,48], metamaterials [49,50] and nanoparticle arrays [51][52][53]. [44] The dimensions of the texturing can be microscopic or macroscopic, and light scattering can be isotropic or anisotropic. The resulting absorption and emission are defined by the geometrical parameters of the structure, such as the dimensions of the patterns (height/depth, distance), its orientation and the layer thicknesses. ...
Concentrated solar power (CSP) plants provide renewable energy thanks to the concentration of solar irradiation by mirrors upon a solar absorber, which converts it first into heat, enabling large-scale thermal storage to mitigate solar intermittence, then into electricity. The lifetime over which performance is expected to be maintained is typically 25 to 30 years for this technology. However, the latter operates under very demanding conditions for materials (highly concentrated solar irradiance/high temperature combined with oxidant/corrosive atmospheric conditions). The main component exposed to these harsh conditions is the solar absorber, susceptible to high deterioration resulting in high sun-to-heat conversion losses. The solar absorber is often covered with a selective absorber coating, to increase the absorption of solar radiation (high solar absorptance) while reducing radiative thermal losses (low emittance). This solution is optically efficient but requires complex multilayer coating architectures which may easily suffer degradations in CSP conditions of use. It is therefore crucial to prove the durability of new solar absorber coating architectures before they can be used in CSP installations. Aging tests must be applied to study their thermal stability, reliability and potential service life. However, no standardized aging procedures for solar absorber coatings exist today. This thesis work thus provides: i) a critical review of existing aging protocols and tools, and identified aging phenomena; ii) a critical analysis of classical (purely thermal) and original (thermal + concentrated solar) aging protocols based on their experimental application to three types of new selective absorber coatings, using two unique aging tools including a solar furnace. The influence of the main sources of degradation in real CSP operation (high temperature, high concentrated solar irradiation, slow/rapid thermal cycling) is investigated and partly decorrelated, by following the evolution with aging of their optical performance, surface state and chemical composition. This work analyses the pertinence of studied aging protocols and tools, and proposes broadly applicable strategies for solar absorber coating developers.
... Spinels are a tightly packed crystal minerals that form in high temperature processes, thereby they help prevent the diffusion of oxygen or metal ions such as chromium, which makes spinel pigments highly stable at high temperatures. In CST applications, spinel pigments are usually held together by a porous binder and have reached absorptance of >97% [8][9][10][11] , but the coating still degrades rather rapidly during operation. The observed optical degradation is due to sintering of the nano-scale morphology, crystallisation of the binder, and cracking 3 , while the mechanical degradation is due to oxide layer growth since the nano-scale porosity is not effective in hindering diffusion of ions 7 . ...
Concentrating solar thermal (CST) is an efficient renewable energy technology with low-cost thermal energy storage. CST relies on wide-spectrum solar thermal absorbers that must withstand high temperatures (> 700°C) for many years, but state-of-the-art coatings have poor optical stability. Here, we show that the largely overlooked macro-scale morphology is key to enhancing both optical resilience and light trapping. Inspired by stony-coral morphology, we developed a hierarchical coating with three tuneable length-scale morphologies: nano- (~ 120 nm), micro- (~ 3 µm) and macro-scales (> 50 µm). Our coating exhibits outstanding, stable solar-weighted absorptance of > 97.75 ± 0.04% after ageing at 850°C for more than 2,000 hours. The scalability of our coating is demonstrated on a commercial solar thermal receiver, paving the way for more reliable high-performance solar thermal systems.
... Zhang and co-workers reviewed various solar absorber coatings and thermal stability test methods, discussed ageing mechanisms and mentioned several commercial applications and challenges [112]. It is thought that cation diffusion from the substrate through the coating, its subsequent oxidisation promoted by the high temperatures and cracks induced by thermal cycling, result in the reduced absorptance and subsequent failure of Pyromark 2500 [113,114]. An expensive re-coating process has to be implemented to cope with the degradation of Pyromark 2500 [115]. ...
... They showed that, on stainless steel (SS253MA), its solar-weighted absorptance was over 0.965 after 100 h of annealing at 850 • C, whereas Pyromark 2500 was found to fail [110]. Rubin and co-workers developed Co 3 O 4 and CuCo 2 O 4 nanoneedles that preserve their high aspect ratio and sharp tips after annealing at 800 • C for 100 h [114], inspired by several exotic nanostructures such as carbon nanotube array [124]. Rubin and co-workers reported a record solarweighted absorptance of 0.990 and 0.993 for the Co 3 O 4 and CuCo 2 O 4 nanoneedles, respectively [114]. ...
... Rubin and co-workers developed Co 3 O 4 and CuCo 2 O 4 nanoneedles that preserve their high aspect ratio and sharp tips after annealing at 800 • C for 100 h [114], inspired by several exotic nanostructures such as carbon nanotube array [124]. Rubin and co-workers reported a record solarweighted absorptance of 0.990 and 0.993 for the Co 3 O 4 and CuCo 2 O 4 nanoneedles, respectively [114]. Nonetheless, the needle morphology could potentially have lower solar-weighted absorptance at steeper incident angles which are common in CSP plants. ...
High-temperature solar thermal energy systems make use of concentrated solar radiation to generate electricity, produce chemical fuels, and drive energy-intensive processing of materials. Heat transfer analyses are essential for system design and optimization. This article reviews the progress, challenges and opportunities in heat transfer research as applied to high-temperature solar thermal and thermochemical energy systems. The topics discussed include fundamentals of concentrated solar energy collection, convection heat transfer in solar receivers, application of liquid metals as heat transfer media, and heat transfer in non-reacting and reacting two-phase solid–gas systems such as particle–gas flows and gas-saturated porous structures.
... MoO 3 with different structures has been prepared by many techniques; including Atomic Layer Deposition, hydrothermal process, Chemical Vapor Deposition, thermal evaporation, sputtering, Electrodeposition, among others [14][15][16][17][18][19][20][21]. However, these approaches have drawbacks that restrict their commercial applications; like complicated preparation, high energy consumption, expensive equipment, or the use of toxic and dangerous reagents [13]. ...
Black Moly (MoO3) coatings obtained by a facile sustainable wet chemical etching method has been investigated to understand the effect of etchant time on the prepared coatings. The effect of the time of etching on the structural, morphological and optical properties of black moly coatings have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and UV–Vis spectroscopy. The XRD spectrum of the prepared coatings showed only peaks from the Molybdenum substrate indicating amorphous coatings. But when annealed at 500˚C, it showed crystallisation to MoO2. In this work, we developed a nanostructured coating, black moly, with a high solar absorptance of over 81%. These results suggest that black moly coatings made from refractory metal oxides can be used for solar thermal absorbers.
The emergence of metamaterials and their continued prosperity have built a powerful working platform for accurately manipulating the behavior of electromagnetic waves, providing sufficient possibility for the realization of metamaterial absorbers with outstanding performance. However, metamaterial absorbers composed of metallic materials typically possess many unfavorable factors, such as non‐adjustable absorption, easy oxidation, low‐melting, and expensive preparation costs. The selection of dielectric materials provides excellent alternatives due to their remarkable properties, thus dielectric‐based metamaterial absorbers (DBMAs) have attracted much attention. To promote breakthroughs in DBMAs and guide their future development, this work systematically and deeply reviews the recent research progress of DBMAs from four different but progressive aspects, including physical principles; classifications, material selections and tunable properties; preparation technologies; and functional applications. Five different types of theories and related physical mechanisms, such as Mie resonance, guided‐mode resonance, and Anapole resonance, are briefly outlined to explain DBMAs having near‐perfect absorption performance. Mainstream material selections, structure designs, and different types of tunable DBMAs are highlighted. Several widely utilized preparation methods for customizing DBMAs are given. Various practical applications of DBMAs in sensing, stealth technology, solar energy absorption, and electromagnetic interference suppression are reviewed. Finally, some key challenges and feasible solutions for DBMAs’ future development are provided.
Selective absorber is an important component for enhancing the solar-to-heat efficiency in high-temperature solar applications. In this paper, a selective metamaterial absorber possessing four-pointed star prisms was proposed and studied. Firstly, an optimal metamaterial absorber with perfect spectrally selective performance was obtained after optimizing the structure. It was found that the optimal absorber can achieve the high total solar absorptance of 0.958 and the low total emittance of 0.2355-0.4062, thus obtaining the high solar-to-heat efficiency of 92.31%-77.78% at 1000 suns and 1273-1673 K. Secondly, the underlying mechanisms for the good spectral selectivity of the optimal absorber were analyzed. The results showed that the high spectral absorptance in the solar spectrum owes to the impedance matching and the coupling effects of different plasmonic modes. The low spectral emittance within the mid-infrared band can be explained by the impedance mismatching. Thirdly, the effects of the geometrical parameters on the spectral selectivity of the absorber were studied, indicating that the height of the SiO2 layer above the star and the short diagonal length of the rhomb influence little on the spectral absorptance when they are in certain ranges. However, other parameters have obvious influences on the spectral absorptance. Finally, study on the effects of the polarization angle and incident angle indicated that the optimal absorber exhibits good insensitivities to the polarization angle and the incident angle. These results indicate that the proposed perfect absorber is a promising candidate for high-temperature solar applications.
CuCr2O4 thin films grown by physical vapour deposition were studied in order to evaluate their potential as absorber material for the next generation of concentrated solar power plants. A series of Cu-Cr-O thin films was deposited by reactive ion beam sputtering. The Cr/Cu ratio in the sputter target is demonstrated as the most important parameter to achieve the intended film stoichiometry. In-air annealing at 800°C leads to structural transformations of the as-deposited films and results in phase compositions according to those expected from the ternary Cu-Cr-O phase diagram. Tetragonal CuCr2O4 with 98.6 at.% phase purity regarding the solid film constituents is obtained for the appropriate Cr/Cu ratio in the sputter target. CuCr2O4 thin films absorb light in the entire solar spectral range from 300 nm to 2500 nm. Their energy gap is found to be < 0.5 eV, and their solar absorptance is estimated to be (0.85 ± 0.03). The dense microstructure with good thermal conductivity, full adhesion to the substrate, and a relatively low surface roughness are discussed as technological advantages of CuCr2O4 thin films grown by physical vapour deposition.
The adoption of nanostructured metal-oxides integrated graphene monolayers-based heterostructures appears to be a promising approach for enhancing the performance of various devices. However, precisely controlled growth of such unique heterostructures without disturbing the monolayer graphene characteristics remains a challenging task especially over a large area with good uniformity. Herein, ultrathin metal-oxide (p-Co3O4 and n-ZnO) nanostructures (MONSs) integrated graphene monolayer (GML) heterostructures are carefully developed by fascinating the graphene native defects while nucleation and growth of MONSs. Metal-oxides integrated graphene monolayers with lower material densities (≤ 30 μg/cm²) significantly enhanced the quality (2D/G ~5–9) and reduced the electrical resistance (11–17 Ω/sq.) of graphene layers, whereas the heterostructures developed with higher densities possess predominant water-oxidation characteristics than that of their individual components. Further, the Co3O4/GML heterostructures-based micro-supercapacitors, fabricated over 25 µm polyimide sheets, showed excellent mechanical stability and flexibility with a volumetric and specific capacitance of 7.76 F/cm³ and 1.27 F/g, respectively. The ZnO/GML heterostructures designed over micron thick parylene film displayed exciting photoresistor characteristics with photosensitivity of ~1.54 and superb flexibility and skin-mountability. Synergistic multifunctional characteristics of these ultrathin heterostructures offer the possibility to realize various eco-friendly ultrathin as well as skin-mountable energy and health monitoring devices.
