Selective Solar Receiver Coating for Low Emissivity at High Temperature
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Solution Overview
Problem
Current selective coatings for solar receiver devices in concentrated solar thermal plants face challenges in maintaining high solar absorbance while minimizing thermal emissivity, especially at high temperatures, leading to inefficiencies in energy conversion due to high emissivity values.
Innovation Solution
A process for producing an optically selective coating on receiver substrates using a multilayer structure comprising a high-melting metal (W) layer, a metal-ceramic composite (CERMET) layer with YPSZ as the ceramic matrix, and an antireflection layer, deposited using DC/RF sputtering without the need for matching layers, optimizing the coating's properties for high absorbance and low emissivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional selective coatings are used on receiver devices, then solar absorbance is achieved, but thermal emissivity increases at high temperatures causing energy loss
Solution Approach 1:
The coating is divided into multiple functional layers: a first CERMET layer (50-150 nm) with metal particles in ceramic matrix for solar absorption, a second CERMET layer (50-150 nm) with different metal-ceramic composition for thermal reflection, and an dielectric layer (100-300 nm) for optical interference. This segmentation allows each layer to specialize in either absorption or emission control, resolving the contradiction between absorbance and emissivity.
Solution Approach 2:
The invention uses CERMET composite materials consisting of metal particles dispersed in a ceramic matrix. The first CERMET layer uses metals like W, Mo, or Ta with ceramics like Al2O3 or ZrO2 for high solar absorbance, while the second CERMET layer uses different metal-ceramic combinations optimized for infrared reflection. This composite structure enables simultaneous optimization of both absorption and emission properties.
2Power
If temperature is increased to improve energy conversion efficiency, then more energy can be extracted, but thermal and chemical resistance of the coating deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the coating layers to achieve high-temperature stability. The CERMET layers use refractory metals (W, Mo, Ta) with high melting points and stable ceramics (Al2O3, ZrO2) that maintain their properties at temperatures up to 550°C or higher. The dielectric layer uses materials like SiO2, TiO2, or Ta2O5 with excellent thermal stability. This parameter optimization allows the coating to withstand elevated operating temperatures while maintaining optical performance.
3Manufacturing precision
If multilayer CERMET coatings are deposited using plasma evaporation, then optical properties are optimized, but manufacturing complexity and cost increase
Solution Approach 1:
The invention extracts and eliminates the matching layer that is traditionally required between the substrate and the first CERMET layer in plasma-evaporated coatings. By using sputtering deposition with optimized process parameters (power, pressure, gas flow), the patent achieves direct adhesion of the first CERMET layer to the substrate, reducing the number of deposition steps and simplifying the manufacturing process while maintaining optical performance.
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 process achieves absorptance values of 0.893 and hemispherical emissivity of 0.087 at 550°C, significantly improving the energy conversion efficiency by reducing heat losses and maintaining mechanical properties.
Implementation Method 1
deposition using DC/RF sputtering
Implementation Method 2
high absorbance to the receiver within the electromagnetic spectrum range which includes solar radiation and a low emissivity within the range of infrared thermal radiation
Implementation Method 3
a first metallic reflecting layer
Implementation Method 4
annealing under the same temperature and pressure conditions as the deposition of the reflecting layer
Data Source
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AI summary
A process for the production of an optically selective coating of a receiver substrate of a suitable material for solar receiver devices particularly suitable for operating at high temperatures, more specifically for receiver tubes of linear parabolic trough, which comprises : deposition of a layer reflecting infrared radiation consisting of a high-melting metal on a heated receiver substrate of a suitable material; annealing under the same temperature and pressure conditions as the deposition of the reflecting layer; deposition on the high-melting metal of one or more layers of metal-ceramic composite materials (CERMET), wherein the metal is W and the ceramic matrix is YPSZ ("Yttria-Partially Stabilized Zirconia"); deposition on the cermet of an antireflection layer; annealing under the same temperature and pressure conditions as the depositions of the cermet and antireflection layers.