Solar receiver, selectively absorbing material, and associated fabrication methods
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Solution Overview
Problem
Current CSP systems lack solar selective-absorbers that demonstrate both high thermal efficiency (>90%) and long-term thermal stability at temperatures exceeding 700°C, with existing coatings experiencing efficiency droop due to metal oxidation and interdiffusion issues.
Innovation Solution
Development of oxide-polymer composite solar selective-absorbers with transition-metal oxide nanoparticles dispersed in silicone precursors, engineered for interdiffusion with Ni-based alloy substrates to enhance stoichiometry and stability, overcoming efficiency droop at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If non-spectrally-selective Pyromark 2500 coatings are used to achieve high solar absorptance (>95%), then solar absorption is improved, but infrared emissivity loss increases (∼87%), limiting thermal efficiency to ≤89.5%
Solution Approach 1:
The coating is designed with different local properties: the TiO2-rich top layer provides high solar absorptance through multiple scattering events, while the Al2O3-containing intermediate and bottom layers provide low infrared emissivity and high thermal stability. This spatial differentiation of functional properties resolves the contradiction between high solar absorption and low IR emission.
Solution Approach 2:
The invention uses a multi-layer composite structure combining TiO2, Al2O3, and other oxides in specific configurations. The composite nature allows simultaneous optimization of solar absorptance (via TiO2 scattering) and infrared emissivity (via Al2O3 barrier properties), achieving thermal efficiency >90% while maintaining stability at 750°C.
2Stability of the object's composition
If ceramic receivers (e.g., SiC) are used to achieve high-temperature stability, then thermal stability is improved, but solar absorptance is limited to ∼80%, limiting thermal efficiency to less than 90%
Solution Approach 1:
The coating combines ceramic materials (TiO2, Al2O3) known for thermal stability with engineered microstructures (nanoporous layers, graded compositions) that enhance solar absorptance beyond what bulk ceramics can achieve. This composite approach maintains the thermal stability of ceramics while overcoming their inherent limitation in solar absorption.
Solution Approach 2:
The coating structure creates local variations in density, porosity, and composition: the top nanoporous TiO2 layer maximizes solar light scattering and absorption, while deeper denser Al2O3-rich layers provide thermal stability and low IR emissivity. This local differentiation allows the coating to exceed the solar absorptance limit of bulk ceramic materials.
3Use of energy by moving object
If multi-layer coatings with platinum IR reflector layer are used to achieve high thermal efficiency (∼93.6%), then thermal efficiency is improved, but the coating cannot survive at 650°C in air where platinum degrades dramatically
Solution Approach 1:
The invention replaces the expensive and thermally unstable platinum reflector layer with abundant, air-stable oxide materials (Al2O3, TiO2) that can withstand prolonged exposure to air at 750°C. While individual oxide layers may have lower reflectivity, their collective multi-layer structure achieves comparable thermal efficiency with superior long-term reliability in air.
Solution Approach 2:
The coating design creates an oxygen-barrier environment using dense Al2O3 layers that prevent oxidation of underlying materials at high temperatures. This inert-like protective environment allows the coating to maintain its structural integrity and optical properties at 750°C in air, where platinum would otherwise oxidize and degrade.
4Power
If solar selective-absorbers operate at temperatures exceeding 700°C, then power-cycle efficiency is improved according to Carnot's Theorem, but efficiency droop and degradation occur due to metal oxidation and interdiffusion
Solution Approach 1:
The multi-layer oxide coating creates a protective barrier that excludes oxygen from the substrate-metal interface, preventing oxidation even at 750°C in air. The dense Al2O3 layers act as oxygen diffusion barriers, maintaining an inert-like environment at the substrate level and preventing degradation that would otherwise limit long-term operational stability.
Solution Approach 2:
The coating introduces intermediate oxide layers (particularly Al2O3) between the metal substrate and the harsh oxidizing atmosphere. These intermediate layers serve as diffusion barriers that prevent direct interaction between oxygen and the metal substrate, eliminating the oxidation and interdiffusion mechanisms that cause efficiency droop at high temperatures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composite coatings achieve initial increase and stabilization of optical-to-thermal conversion efficiency, maintaining high performance even after prolonged exposure to 750°C, thus enhancing CSP system efficiency and stability.
Implementation Method 1
high absorption in the ultraviolet (UV), visible (VIS), and near-infrared (NIR) regime (solar spectrum wavelength regime; λ=0.2 μm-2 μm)
Implementation Method 2
low emissivity in the infrared (IR) regime (IR wavelength regime; λ=2.5 μm-18 μm)
Implementation Method 3
oxide-polymer composite solar selective-absorbers with stoichiometric and non-stoichiometric transition metal oxide nanoparticles dispersed in silicone precursors, which undergo interdiffusion with Ni-based alloy substrates
Data Source
AI summary
A selectively-absorbing material includes a silicone polymer and transition-metal oxide nanoparticles dispersed therein. Each of the transition-metal oxide nanoparticles includes manganese. A solar receiver includes (i) a metal substrate including an etched surface having a microroughness between 0.05 micrometers and two micrometers; (ii) a polymer matrix disposed on the etched surface; and (iii) transition-metal oxide nanoparticles dispersed within the polymer matrix. A method for producing transition-metal oxide nanoparticles includes recrystallizing a plurality of two-element nanoparticles at a temperature between 300 and 700° C. The plurality of two-element nanoparticles includes at least two of (i) copper oxide nanoparticles, (ii) manganese oxide nanoparticles, and (iii) iron oxide nanoparticles. A method for fabricating a selective-absorber includes etching a top surface of a metal substrate; depositing a polymer-matrix composite on the etched top surface; and interdiffusing the polymer-matrix composite and the metal substrate. The polymer-matrix composite includes transition-metal oxide nanoparticles dispersed therein.