Selective Absorber Coatings Research Articles

Analysis of solar absorption, degradation mechanism and thermal stability in air environments for SS/TiB2/Al2O3 spectrally selective absorber coating

The quest for high solar-thermal conversion efficiency and thermal stability is a significant challenge in the development of high-efficiency spectrally selectivity absorber coatings. A key aspect of this challenge is the creation of air-stabilized coatings, particularly crucial for scenarios involving unexpected vacuum loss or applications of concentrating solar power systems in air environments. In our study, TiB2 films own excellent spectral selectivity and thermal stability at air environment. In pursuit of revealing the absorption mechanism of the coating, the optical constants, absoption and transmission of the single TiB2 layer were measured. The result of analysis display that the TiB2 layer contribute the bulk of the sunlight absorption. Reflectance spectra of the SS/TiB2/Al2O3 coating was succeeding simulated by CODE software with the optical constant to fit the experimental spectra, which confirms the results obtained by spectroscopic ellipsometry. The solar-thermal conversion efficiency of the as-deposited coating could reach 88.9 % of 100 suns at 500 °C. After annealing at 300–500 °C, the absorbance and emittance of the coating change slightly. But after annealing at 600 °C, the changing surface morphology, increasing surface roughness, and oxidation reaction of TiB2 resulted in a decrease in the optical performance of the coating.

BiFeO3 perovskite-based all oxide ambient stable spectrally selective absorber coatings for solar thermal application

Enhancements in absorbance and thermal stability are essential for solar selective absorber coatings (SSACs) to convert solar energy efficiently into thermal energy.

Thermal stability of AlCrO antireflection layer for high-temperature cermet-based solar selective absorber applications

Highly stabled antireflection layers play a crucial role in enhancing the optical and thermal performance of cermet-based solar selective absorbing coatings. Few state-of-the-art antireflection layers are qualified for high-temperature (>873 K) utilizations due to the insufficient thermal stability and increased infrared emissivity. Herein, a highly stable multilayer cermet-based absorber with an AlCrO antireflection layer is developed using cathode arc ion plating. The deposited coating exhibits a solar absorptivity of 0.908 ± 0.005 and a thermal emissivity of 0.144 ± 0.004 even after annealing at 923 K for 2000 h in air, compared to the pristine coating with a spectral selectivity of 0.898 ± 0.002/0.186 ± 0.003. After undergoing the extensive annealing treatments, abundant particles with an average size of approximately 8 μm have been detected on the coating surface. However, the AlCrO layer exhibits a remarkably flawless and dense surface topography devoid of any cracks or voids. Based on the GI-XRD and TEM evaluations, the particles have been identified as Mn2O3 nanocrystals. The formation of Mn2O3 particles originates from the diffusion of Mn atoms from the stainless-steel substrate to the surface of the AlCrO layer, where they undergo oxidation. The presence of Mn2O3 can enhance the solar absorptivity by increasing transmittance in the visible light spectrum and reduce the emittance by enhancing reflection of infrared radiation. Then, the impact of Mn2O3 on spectra selectivity and thermal stability is discussed. These results indicate that the AlCrO layer exhibits remarkable durability when subjected to high-temperature annealing in an air environment, thereby significantly enhancing the thermal stability and optical performance of cermet-based solar selective absorbing coatings. These findings suggest that the AlCrO layer exhibits exceptional durability under high-temperature annealing in an air environment, thereby significantly enhancing the thermal stability and optical performance of cermet-based solar selective absorbing coatings.

Facile dip-coating assisted preparation of reduced graphene oxide-copper oxide nanocomposite thin films on aluminum substrate for solar selective absorber

Reduced graphene oxide integrated copper oxide nanocomposite thin film (rGO-CuO NC TF) solar selective absorber coatings were devised on aluminum substrate using dip-coating procedure. The prepared coatings were subjected to characterization by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, PL spectroscopy, UV–vis–NIR spectrophotometer, Emissometer and Raman spectroscopy. XRD and Raman analyses disclosed presence of mono-phase with highly crystalline monoclinic structured CuO in the rGO-CuO NC TFs. The SEM images revealed grain-like morphology of CuO, which are randomly distributed on rGO sheets. EDX and XPS investigations confirmed presence of anticipated chemical constituents and chemical composition, respectively in the NC TFs. The rGO-CuO NC TF with 1.0 wt% GO disclosed absorptance (α) of 79.92% and emittance (ε) of 4.2% with a highest selectivity (ξ) of 19.03 that suggests its promising prospect for solar absorber coating in solar thermal devices.

Enhanced high-temperature thermal stability of the novel MoAlSiN-based solar selective absorbing coatings by optimizing the multilayer structure

Solar selective absorbing coating (SSAC) plays an important role in the high-temperature concentrated solar power system. The high thermal stability of SSAC above 600 °C has been a big open question for molten salt concentrated solar power projects. In our work, the TiN/Mo/MoAlSiN/MoAlSiON/SiO2 and the TiN/Mo/MoAlSiN/Si3N4/SiO2 SSACs are developed for getting high-temperature thermal stability, besides excellent spectral selectivity. The solar spectral absorptivities of the MoAlSiN/MoAlSiON and MoAlSiN/Si3N4 SSACs are 95.2% and 93.2%, respectively. While the infrared emissivities of the MoAlSiN/MoAlSiON and MoAlSiN/Si3N4 SSACs are controlled below 10.6% and 10.5% at 400 °C, respectively. The novel MoAlSiN/Si3N4 SSAC deposited on quartz can maintain thermal stability even after heat treatment at 800 °C for 200 h in vacuum, which is one of the best results in the research field for high-temperature SSACs. It is found that the choice of suitable materials without oxygen and the elimination of interfacial thermal stress are very important for improving thermal stability. Furthermore, the practical total energy conversion efficiencies of the MoAlSiN/Si3N4 SSAC at 600 °C–800 °C are always above 57%. When the activation energy is assumed as 180 kJ/mol, the estimated service life of the MoAlSiN/Si3N4 SSAC at 600 °C is more than 25 years.

Realizing an Optical Micro‐Cavity in a CuCo2O4‐W‐CuCo2O4 Thin Film Stack for Spectrally Selective Solar Absorbers

AbstractTapping the potential of solar thermal energy requires spectrally selective solar absorber coatings, which lead to high photothermal efficiency. Micro‐cavities are known to dramatically enhance or suppress light absorption and emission in a directional manner and are used in nanophotonics, photodetectors, lasing, etc. Here, a dielectric‐metal‐dielectric multilayer stack with an optical micro‐cavity of a 12 nm tungsten layer formed between two dielectric layers of transition metal oxide CuCo2O4 (CCO) is designed. The CCO‐W‐CCO thin film multilayers deposited on stainless steel substrate by DC‐radio frequency magnetron sputtering achieve a 90% solar absorptance for the entire solar spectrum and a thermal emittance of 19% for the infrared spectrum. Optimization of thicknesses of individual layers is achieved by numerical simulations done in COMSOL Multiphysics, thereby reproducing the optical properties of each layer. The simulation results satisfactorily reproduce the experimental reflectance and demonstrate maximum power dissipation in the metallic layer in visible as well as NIR regions. Nevertheless, CCO material characterizations reveal that the enhanced absorption over the entire solar spectrum could be attributed to the underlying spinel crystal structure and the nanostructure film morphology.

Improved optical and mechanical characteristics of multilayered Cu/TiON/CrO2 coating via heat treatment for solar absorbing applications

In the last few decades, growing interest has been shown in the development of new solar selective coatings based on transition metal nitride and/or oxinitride for solar absorbing applications. Solar thermal collectors are well thought out to be the most effective process of converting and harvesting solar radiation. In this investigation, Cu/TiON/CrO2 multilayered solar selective absorber coatings have been coated onto Al substrates using the dip-coating process followed by an annealing process at (400, 450, 500, 550, and 600 °C. The XRD analysis showed excellent crystalline quality for the prepared thin films along with enhanced surface features as proved by FESEM images, and the grains are in the range of (27–81) nm. The optical investigations revealed that the film annealed at 600 °C exhibits improved solar absorptance, thermal emittance, and solar selectivity of ~ (90.7 %), (5.8 %) and 15.6, respectively. Also, the highest values of hardness ~ (26.8 GPa) and Young’s modulus ~ (250 GPa) were assigned for the film annealed at the highest temperature. Calculated optical band gaps of fabricated thin multilayered Cu/TiON/CrO2 films were found to be in the range of (1.8 – 2.10) eV.

Extracting Optical Parameters of Cu–Mn–Fe Spinel Oxide Nanoparticles for Optimizing Air-Stable, High-Efficiency Solar Selective Coatings

High-temperature Cu–Mn–Fe spinel-oxide nanoparticle solar selective absorber coatings are investigated experimentally and theoretically. A general realistic approach to evaluate absorption coefficient spectra from the optical measurements of the nanoparticle-pigmented coatings is developed by solving the inverse problem of the four-flux-radiative transfer model. The derived absorption properties are utilized to elucidate the direct and indirect bandgap transitions in the visible spectral regime as well as the sub-bandgap absorption in the infrared range. Furthermore, the optical properties of NP materials can be directly applied to optimize the solar selective coating design and analyze thermal degradation mechanisms. The analysis reveals that the Cu–Mn–Fe spinel oxides are semiconductors with an indirect bandgap ranging from 1.7 to 2.1 eV, while iron-free CuMn2O4 is a direct bandgap material with Eg = 1.84 eV. With the same coating thickness and nanoparticle load, the solar absorptance ranks in the order of Mn2O3 < MnFe2O4 < CuFe2O4 < CuFeMnO4 < CuMn2O4. The optimized spray-coated iron-free CuMn2O4 NP-pigmented coating demonstrates a high solar absorptance of 97%, a low emittance of 55%, a high optical-to-thermal energy conversion efficiency of ∼93.5% under 1000× solar concentration at 750 °C, and long-term endurance upon thermal cycling between 750 °C and room temperature in air. The optical parameter analysis approach can be easily extended to other material systems to facilitate the search and optimization of high-temperature nanoparticle-pigmented solar selective coatings.

Optical and thermal performance analysis of a compact solar collector with heat-pipe evacuated tube

Process industry consumed 15 % to 30 % of the global energy, and 40 % of it is thermal energy demand in the range of 80 °C-250 °C. To produce mid-temperature heat, a new solar collector was designed with heat pipe evacuated tube, including several parallel micro-parabolic troughs, heat pipes, double-layer vacuum tubes contained in a compact frame and an external mechanical solar tracker. In addition, the selective absorbing coating (SAC) was applied on the inner surface of the vacuum tube, and the gap between the heat pipe and the vacuum tube was filled with heat transfer oil. Since the height of the designed collector was only 124.5 mm, it can be easily integrated with buildings. Genetic algorithm (GA) was used to optimize the structural parameters based on maximum obtained solar energy of the collector, and theoretical analysis and numerical simulation are carried out for optical and thermal performance of the collector. The analytical and numerical results showed that the annual average optical efficiency is 57.6 % and the thermal efficiency is 30.6 % at 250 °C when the normalized temperature difference is 0.23. By exergy analysis, the collector has a maximum exergy efficiency of 15.5 % with operating temperature of 204.4 °C, which is the station of the best thermal performance of the collector. Furthermore, theoretical model was verified to be valid by a prototype. Overall, the proposed collector is suitable for mid temperature industrial applications and integrated with rooftop.

High-temperature thermal stable solar selective absorbing coating based on the dielectric-metal-dielectric structure

Obtaining high-temperature thermal stable solar selective absorbing coatings is a big challenge for ultra-high temperature solar-thermal conversion applications. In this paper, a dielectric-metal-dielectric (DMD) structured solar selective absorbing coating (SSAC), AlN/TiB2/AlN/Mo/AlN/substrate is proposed and then prepared by direct current magnetron sputtering. The as-deposited SSACs have a high absorptance of 93.4% and a low emittance of 6.9% at room temperature. The SSACs with the DMD structure deposited on the stainless steel (SS) substrate can maintain stability at 800 °C for 200 h in vacuum. The performance criterion (PC) value, a key factor to evaluate thermal stability, is only 0.010 for the coatings after heat treatment. The SSACs deposited on the quartz substrate can even remain stable at 900 °C with a low PC value of 0.008. Our findings will have great potential applications in ultra-high-temperature solar-thermal conversion, and satisfy fully the requirements of thermal stability for current CSP projects.

Structural and optical properties of DC sputtered AlxOy/Cr/AlxOy multilayer selective absorber coatings

AlxOy/Cr/AlxOy multilayered selective absorber was theoretically optimized using the individual layers’ optical constants acquired through fitting the transmittance and reflectance measurements into SCOUT software. The optimized multilayer was deposited onto polished aluminium substrates by DC magnetron sputtering at room temperature. The structural analysis of the multilayer stack revealed low crystalline diffraction peaks of Cr at 2θ ≈ 43.3° ascribed to (110) diffraction plane of BCC Cr metal. However, due to the amorphous nature of the deposited films, no AlxOy phase was detected by XRD. SEM and AFM analysis revealed the uniformly and densely distributed small grains with a considerably average surface roughness of ∼5.6 nm. The deposited AlxOy/Cr/AlxOy multilayered stack was found to have an optical absorptance of 0.91 and thermal emittance of 0.12 at a temperature of 373 K, which is potential and suitable for selective solar absorbers applications.

Research on the Thermal Stability in High-Temperature Air of Cr-Fe Composite Oxide Solar Coatings by Chemical-Colored of Stainless Steel

The stainless steel chemical coloration demonstrates excellent repeatability of process when adopted to fabricate solar selective absorber coatings (SSACs) on TTS445J1 stainless steel base material. The optical performance, morphology, and composition of coatings are characterized by UV-3600, IR-Affinity-1, SEM, EDS, etc. The experimental results suggest that the Cr-Fe composite oxides with coatings in a spinel structure obtained by chemical coloration on a stainless steel surface exhibit outstanding spectral selectivity, with α/ε = 0.9334/0.1326. The coatings were generated by the direct reaction between the stainless steel substrate composition and the coloring solution, which changes the traditional way of combining the coating with the substrate by physical methods. Comparing the SEM images of the coatings before and after aging at 500 °C in air, we noticed no significant changes at the interface between the coatings and the substrate, indicating excellent coating adhesion. At the same time, the substrate grains did not change much after the chemical reaction of the stainless steel substrate, indicating that the oxidation resistance of the stainless steel substrate was not weakened. Finally, the Cr-Fe composite oxide exhibited excellent thermal stability in air. Based upon a microstructure analysis, the Performance Creation (PC) is 0.01 after aging at 500 °C for 200 h in high-temperature air, primarily because of the loss of H2O molecules from the hydrates in the coatings. After aging for 800 h, PC = 0.0458. After the aging hours are extended to 1000 h, PC = 0.0762. During the aging process at high temperature, the coatings of the Cr-Fe composite oxides maintained stable composition and phase structures. The decay in optical performance is due mainly to the reconstruction of the surface morphology of the coatings as a result of the largening of grains.

Cobalt-rich spinel oxide-based wide angular spectral selective absorber coatings for solar thermal conversion applications

Solar energy conversion technologies attain enormous attention to create more efficient energy production sources to meet the current world's demand. The solar thermal conversion system converts solar energy to heat, and the receiver tube is crucial for achieving high photo-thermal conversion efficiency. The absorber coatings with high solar absorptance at normal and wide incidence angles of solar radiation improve the performance of concentrated and non-concentrated solar thermal systems. To achieve high photo-thermal conversion efficiency in the solar thermal conversion system, a novel spinel structured cobalt-rich transition metal oxide-based absorber coating was developed by a cost-effective wet chemical route. The developed absorber coatings with sub-micron scaled surface protrusions with porous structure (size 0.75 μm) exhibit an excellent spectral selectivity (α/ε = 0.91/0.13). In addition, the coatings show an excellent wide angular solar absorptance of 0.97–0.96 at incidence angles of 10°–40°. Extensive characterization has been carried out to analyze the structural properties of the absorber coatings and correlated to the spectral selectivity and wide angular solar absorptance property. The stability of the absorber coating at 400 °C for 100 h in an open-air atmosphere assessed by the performance criteria (PC) function value of 0.015 indicates the ability of the optimized absorber coatings to employ in solar thermal systems.

In-Situ Resistance Optimization for ALD Nanocomposite Resistive Materials

Atomic layer deposition (ALD) made resistive nanocomposite materials can be used in many emerging applications such as charge draining layers for electron optic and MEMS devices, functional resistive layers in electron/ion amplifying microchannel plates (MCPs) which are used in photodetectors and mass spectrometry, HF resistance with tunable electrical conductivity coatings for stabilizing Li-ion battery cathode materials, selective solar absorbing coatings for concentrated solar power (CSP), and barrier and encapsulation coatings. Over the last decade, we have worked broadly on the research and development of resistive nanocomposite coatings. In this context, we have developed many nanocomposite materials with tunable resistance based on mixing conducting ALD metal and insulating ALD metal oxide or metal fluoride processes. These ALD nanocomposite materials show robust material performance in many of the applications listed above. Here we are particularly targeting a functional resistive coating that now commercially used for manufacturing large area ALD-MCPs. For this, there are two key topics that we are addressing a) Minimum thickness requirement for resistive coating which provides a stable targeted resistance behavior for MCPs, and b) Can we tune the temperature coefficient of resistance (TCR) of the ALD nanocomposite materials so that the ALD MCPs can operate over a wide temperature range without affecting their performance. To address these two topics, we have utilized in-situ resistance monitoring during the ALD nanocomposite process. With this method we have optimized resistive nanocomposite material ALD processes e.g. (M:Al2O3 where M= W and Mo) for MCPs and also targeted the desired TCR of the materials and achieved ultra-low TCR values. We believe these optimized coatings will reduce the ALD-MCP processing time substantially and enable ALD-MCPs and photodetectors to operate over a broader temperature range compared to existing ALD-MCPs.

Nanoparticles based single and tandem stable solar selective absorber coatings with wide angular solar absorptance

Solar selective absorber coatings with wide angular solar absorptance aids in attaining high photo-thermal conversion efficiency for solar thermal systems. In this regard, nanoparticles-based absorber coatings were developed on stainless steel grade 304 by combining the impregnation method, solvothermal process, and dip-coating technique. Developed nanocomposite (SiO 2 nanoparticles in transition metal oxide matrix) based single layer absorber coating with nano void textured surface, exhibits solar absorptance of 0.92 and spectral emittance of 0.12. MgF 2 nanoparticles based anti-reflective layer on single-layer absorber coating improves the solar absorptance to 0.94 by destructive interference mechanism. Both nanoparticles based single and tandem absorber coatings show wide angular solar absorptance of 0.88 and 0.89, respectively, at an incidence angle of 50°. Besides, developed absorber coatings show lower thermal emissivity of 0.17 and good photo-thermal conversion efficiencies at high operating temperatures (400–500 °C). These developed absorber coatings offer excellent thermal stability at an open atmospheric condition till operating temperature, such as 400 °C for 100 h. Selective nature with wide angular solar absorptance and low heat loss behaviour of stable absorber coating show the photo-thermal conversion efficiency of 91% can improve the performance of receiver tubes in solar thermal systems. • Cost-effective and novel nanoparticles based single and tandem absorber coatings. • Nanocomposite based absorber coating exhibits wide angular solar absorptance. • Tandem layer (MgF 2 AR/nanocomposite) absorber shows solar absorptance of 0.94 • Absorber coatings shows excellent photo-thermal conversion efficiencies (>90%). • Absorber coatings are thermally stable at 400 °C for 100 h with good adhesion.

DC Sputtering Deposition of Copper Oxide Thin Films Doped with Carbon for Efficient Solar Selective Absorbers

In this work, carbon-doped copper oxide thin films were deposited by the reactive DC sputtering method for use as selective absorbents. The properties of the DC discharge plasma were studied, using the emission spectrum, in the presence of pure argon and by mixing it with oxygen once and carbon dioxide again to know the effect of adding these gases on the properties of the resulting plasma used in the deposition of films. The structural properties of the deposited thin films prepared with different flow ratio of carbon dioxide gas were studied using x-ray diffraction. To examine the selective absorber coatings, the reflectance within the UV-Vis spectrum was measured to calculate the percentage of energy absorbed by solar radiation using numerical integration. The reflectance was also measured in the range from 2.5 to 25 μm to calculate the thermal emission of the solar heater within a temperature of 373 K. Measurements showed good efficiency as a selective absorption layer. The best absorptance of the solar spectrum (α) was 0.8750, and the lowest emittance (ε) in the infrared region was 0.254 at 25% percentage of carbon dioxide in the reactive gas of the sputtering system. So, this ratio has the highest efficiency as a selective absorber.

Angular absorptance and thermal degradation analysis of TiB2/Ti(B,N)/SiON/SiO2 multilayer solar absorber coating

AbstractMultilayer solar selective absorber coatings have been developed in the last few decades. The thermal stability in terms of microstructure gives an insightful understanding of the optical properties of such coatings. In this context, we extensively utilized transmission electron microscopy (TEM) analysis to establish the thermal stability of TiB2/Ti(B,N)/SiON/SiO2 coating, under thermal cycling/continuous heating to 500°C in vacuum for 250 h. In particular, this work reports the variation in the solar absorptance of TiB2/Ti(B,N)/SiON/SiO2 coating with different angles of incidence of the solar radiation. Extensive analysis using the TEM technique reveals the presence of oxide interlayers that act as diffusion barrier layers to enhance the thermal stability of the coating. Computational simulation using SCOUT software validates the measured reflectance spectrum of the developed multilayer coating. The minor changes in absorptance and emissivity after heat treatment in vacuum at 500°C, together with high solar absorptance over a broad angular variation, establish the potential application of TiB2/Ti(B,N)/SiON/SiO2 as a selective coating in concentrated solar power systems.

Selective Absorber Coatings and Technological Advancements in Performance Enhancement for Parabolic Trough Solar Collector

Parabolic trough solar collector systems are the most advanced concentrating solar power technology for large-scale power generation purposes. The current work reviews various selective coating materials and their characteristics for different designs in concentrating solar power. Solar selective absorbing coatings collect solar radiation and convert it to heat. To promote higher efficiency and lower energy costs at higher temperatures requires, this study aims to analyse the fundamental chemistry and thermal stability of some key coatings currently being used and even under investigation to find reasons for differences, information gaps and potential for improvement in results. In recent years, several novel and useful solar absorber coatings have been developed. However, qualification test methods such as corrosion resistance, thermal stability testing and prediction of service life, which have essential technical value for large-scale solar absorbers, are lacking. Coatings are used to enhance the performance of reflectors and absorbers in terms of quality, efficiency, maintenance and cost. Differentiated coatings are required as there are no uniformly perfect materials in various applications, working conditions and material variations. Much more knowledge of the physical and chemical properties and durability of the coatings is required, which will help prevent failures that could not be discovered previously.

VO2:Ge based thermochromic solar absorber coatings

Flat plate solar collectors face the problem of overheating and the ensuing high thermal stresses and general collector damage lead to high maintenance costs. To address this challenge, absorber coatings with a passive optical switch at critically high operating temperatures are proposed. The remarkable near- and mid-infrared spectral modulation of thermochromic VO 2 makes it a promising material for smart selective absorbers with temperature dependent optical selectivity. Single VO 2 films readily achieve thermal emittance modulations of 40% points (p.p.) at a phase transition temperature of 66 °C. With 5 at.% Ge added to the VO 2 thin film, the transition temperature is increased to 82 °C. When VO 2 and VO 2 :Ge films are combined with a selective CuCoMnO x layer and an SiO 2 top layer, a thermal emittance modulation of 31 p.p. and 33 p.p. is retained, respectively. However, a simultaneous increase of the solar absorptance α sol by 7 p.p. and 5 p.p. limits the drop in collector efficiency at elevated temperatures. Simulations show that adding an absorber layer between the Al substrate and thermochromic VO 2 , decreasing solar absorptance over the phase transition is achieved. In line with these findings, a TiAlSiN//VO 2 :Ge//SiO 2 multilayer is prepared. Below the phase transition temperature, the efficiency of the thermochromic collector is similar to that of standard collectors. At the transition temperature, α sol decreases from 0.93 to 0.91 and ϵ th increases from 0.08 to 0.24. Such a decrease in α sol accompanied by an increase in ε th for increasing temperature has been achieved for the first time. The subsequent drop in selectivity, limits the maximum stagnation temperature of the thermochromic collector to 160 °C, 17 °C lower than for a standard collector in identical conditions. The absorber durability is confirmed through accelerated aging tests in dry and humid conditions alike. • Thermochromic VO 2 and VO 2 :Ge based selective absorber coatings are deposited. • ε th increases at 66 °C for VO 2 and 82 °C for VO 2 :Ge with 5 at.% Ge. • First absorber designs with both increasing ε th and decreasing α sol are reported. • High collector efficiencies and reduced stagnation temperatures are achieved. • Accelerated aging test in dry and humid conditions are successfully completed.

First principle calculation of thermal conversion properties of W-Al2O3 based solar selective absorbing coating

Al2O3 based solar selective absorbing coatings have been considered as a promising candidate for solar thermal conversions, but their properties are expected to be improved urgently. Herein, inspired by the composite materials design, an optimization method for optical performance and thermal stability of Al2O3 was explored by us, the W-Al2O3 based composite structures used for solar was developed, and its electronic structure and optical performance were investigated by the first-principles calculations. It was found that the band gap of the proposed composite structure can be successfully regulated and it decreases significantly with the increase of the mass fraction of W doped in Al2O3, which leads to the improvement of the thermal stability. The optical properties and solar thermal conversion properties of W-Al2O3 based selective absorption coating are accurately predicted. The results show that W-Al2O3 based solar selective absorption coating also has good absorption and reflection properties. The addition of W atom leads to the reduction of solar thermal efficiency. When the W mass fraction doped in W-Al2O3 is 23.92% at the temperature of 273 K, compared with pure Al2O3, the solar thermal conversion efficiency is reduced by 6.56%, and the corresponding absorption rate and thermal radiation was reduced by 6.54% and 1.99%, respectively.