Process for producing an element for absorbing solar radiation for a thermal concentrating solar power plant
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Solution Overview
Problem
Current selective coatings for solar radiation absorber elements in concentrated solar thermal power plants fail to simultaneously meet performance and durability requirements, especially at high operating temperatures above 400°C and in oxidizing atmospheres, leading to increased manufacturing costs and stability issues.
Innovation Solution
A method for producing a solar radiation absorber element with a high-performance, durable, and stable selective coating on a stainless steel substrate, involving surface polishing and heat treatment in an oxidizing atmosphere with at least 5% oxygen precursor between 550°C and 650°C, forming a thin intrinsically selective superficial layer with a thickness greater than 70 nm on stainless steel with an aluminum content greater than 0.5% by weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional selective coatings are used on stainless steel substrates, then solar radiation absorption performance is improved, but durability and stability at high temperatures above 400°C in oxidizing atmospheres deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the stainless steel substrate by specifying precise ranges of aluminum (0.5-2.0 wt%), silicon (0.05-0.5 wt%), and other alloying elements. These compositional parameter changes enable the formation of a stable oxide layer that maintains both optical performance and durability at high temperatures in oxidizing atmospheres
Solution Approach 2:
The invention creates a composite structure where a selective coating layer is formed on a specially composed stainless steel substrate. The multi-layer system includes the coating layer with specific optical properties and the substrate with optimized chemical composition, working together to achieve both high solar absorption and long-term stability in harsh environments
2Use of energy by moving object
If complex multi-layer interference filters are used to achieve excellent selective performance, then optical performance is improved, but manufacturing complexity and difficulty increase
Solution Approach 1:
The invention extracts and utilizes the natural oxide formation capability of aluminum-containing stainless steel substrates. By leveraging the substrate's inherent tendency to form stable oxides in oxidizing atmospheres, the invention simplifies the coating structure while maintaining excellent selective optical performance, avoiding the need for complex multi-layer interference filters
Solution Approach 2:
The invention enables the substrate to self-form a protective and optically functional oxide layer through controlled exposure to oxidizing atmospheres at elevated temperatures. This self-organizing process creates the selective coating structure without requiring complex external deposition equipment or multi-step manufacturing procedures
3Reliability
If vacuum envelope protection is added to protect selective coatings at high temperatures, then coating durability is improved, but manufacturing cost increases
Solution Approach 1:
The invention converts the harmful oxidizing atmosphere at high temperatures into a beneficial process that forms a protective and optically functional oxide layer on the substrate. Instead of trying to prevent oxidation through vacuum envelopes, the invention utilizes oxidation to create the desired selective coating, eliminating the need for expensive vacuum protection systems
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 solution achieves efficient absorption of solar energy and minimal infrared radiation re-emission, ensuring stability and performance at temperatures above 400°C, including in oxidizing conditions, while being cost-effective and easy to implement on an industrial scale.
Implementation Method 1
heat treatment of the substrate, in an oxidizing atmosphere containing at least 5% by volume of an oxygen precursor, in a range of temperatures between 550°C and 650°C, to form at the outer surface of the substrate, at least one thin intrinsically selective superficial layer
Implementation Method 2
The selective coating is intended to allow maximum absorption of incident solar energy while re-emitting as little infrared radiation as possible
Implementation Method 3
reflects all the wavelengths above this same cut-off wavelength
Implementation Method 4
the surface treatment by polishing the substrate
Data Source
Figure 1~5
Figure 6~7
AI summary
An element for absorbing solar radiation, for a thermal concentrating solar power plant, is produced by forming a selective coating (5) on an external surface of a substrate (2) made of a stainless steel chosen from stainless steels having an aluminium content higher than 0.5 wt%. The selective coating (5) is formed in a surface treatment step, by polishing the substrate and then a step of heat treating the substrate in an oxidizing atmosphere in a range of temperatures lying between 550oC and 650oC. The heat treatment in particular allows at least one thin intrinsically selective superficial layer (1) to be formed on the external surface of the substrate.