World’s Highest Absorption and Durability Coating for High-temperature Solar Thermal Receivers

1. Introduction
Nano Frontier Technology (NFT), in collaboration with Shinshu University and the Australian National University, has developed a coral-structured solar absorber coating with high absorption and durability, specifically designed for receivers in Concentrated Solar Power (CSP) systems [1]. Our unique coatings are applied to heated substrates to create high performance solar absorption and durability with a coral-structure. In this study, we summarize the coating fabrication process and report on its performance together with the latest experimental results in a laboratory environment, in the field using a drone-assisted deposition and using a robot-assisted deposition to a heated commercial receiver.
2. Experimental Details
2.1. Sample preparation
We prepared two types of ink. ‘NFT Black’ and ‘NFT Top’. We use ‘NFT Black’ for both the base layer and the absorption layers. By changing the spray conditions, it is possible to create coating with different structures. Titanium precursor reacts with acetylaceton then add black spinel pigments and additives. For the top layer coating, ‘NFT Top’, a mixture of polymerized silica and silica nanospheres, was used [2].
2.2. Application method
In the laboratory test, place the substrate on a hot plate and heat it to the appropriate temperature. For the base layer, the substrate was heated at 270°C and for the absorption layer and top layer, the substrate was heated at 300°C. A two-fluid spray gun was used to create a uniform, precious coating. In the field test, commercial receiver with dimensions of 2 x 2 m was prepared. To create coral-structured coating we have developed, the surface of the receiver tube needs to be heated when coating. Heated oil was circulated through the receiver tube during coating. For the coating test, we prepared the robotic arm and drone equipped with a spray nozzle.
3. Result
In all lab and field tests (both robotic and drone), we were successful in creating a coating with a coral-like structure. Even after the long term aging test, the coatings did not peel off or deteriorate. In the laboratory tests, the absorptance of the coating remained over 96% even after 3000 hours of aging at 850°C. Our coating had almost 2% higher absorptance than Pyromark 2500, the state-of-the art coating in CSP. The coating created by the robot and drone also showed high light absorption and durability.
4. Conclusion
In this study, a novel solar absorber coatings is shown to be more durable than Pyromark 2500 after aging at high temperature. Importantly, this coral-structured coatings did not fail when coated on the substrate SS316L, whereas Pyromark reportedly failed after around 900 hours. The coating deposited by the robotic arm and drone showed high absorption and durability, just as in the laboratory tests. This coating approach enables us to coat uniformly on the receiver while reducing maintenance application time and labor costs. Futhermore, the use of a robotic arm and drone eliminate serious safety hazards for operators, compared to those who manually coat receivers placed at elevated heights.
References
[1]J. F. Torres, K. Tsuda, Y. Murakami, Y. Guo, S. Hosseini, C-A. Asselineau, M. Taheri, K. Drewes, A. Tricoli, W. Lipinski and J. Coventry. “Highly efficient and durable solar thermal energy harvesting via scalable hierarchical coatings inspired by stony corals”, Energy & Environmental Science 15, 1893 (2022) DOI: 10.1039/d1ee03028k
[2]Y. Guo, K. Tsuda, S. Hosseini, Y. Murakami, Antonio Tricoli, J. Coventry, W. Lipinski, and J. F. Torres, “Scalable nano-architecture for stable near-blackbody solar absorption at high temperature”, Nature Communications 15, 384 (2024) DOI: 10.1038/s41467-023-44672-3
[3]Y. Guo, K. Tsuda, M. Mohsenzadeh, S. Hosseini, Y. Murakami, J. Coventry and J. F. Torres. “Titania-based coral-structured solar absorber coating with improved scalability and durability at high temperature”, Advanced Science, 2407409 (2024) DOI: 10.1002/advs.202407409