Solar Coatings Based on Ag Infrared Reflector with High Stability at Medium and High Temperature

Salvatore Esposito,Antonio Guglielmo,Michela Lanchi,Antonio D’Angelo,Claudia Diletto,Gabriella Rossi

doi:10.3390/en14185910

Salvatore Esposito, Antonio Guglielmo + Show 4 more

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https://doi.org/10.3390/en14185910

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Abstract

The manufacturing of thermally stable solar coatings with high photo-thermal performance represents a key factor for the further deployment of the CSP technology. Since 2005, ENEA has been developing solar coatings suitable for medium and high temperature applications based on the technology of double nitride cermet, by employing silver and tungsten as infrared reflectors, respectively. Thanks to the high infrared reflectance of silver, the corresponding coatings have better optical performance than those with tungsten; however, the high diffusivity of silver compromises its use at high temperature. In order to improve the structural and chemical stability at medium and high temperature of coatings based on silver, this infrared reflector was placed between compact and uniform layers of metal and cermet manufactured by using high-energy and fast deposition processes. In particular, an Unbalanced Magnetron cathode was adopted to promote an ion-assisted deposition process that improved uniformity and compactness of the metal and cermet films. The new coating shows no photo-thermal parameters degradation after 25 years of service at the operating temperature of 400 °C, while its photo-thermal conversion efficiency decreases by only 1.5% after 25 years of service at an operating temperature of 514 °C.

Highlights

Concentrating Solar Power (CSP) technology can be considered as a mature technology for large-scale renewable energy production [1,2], destined to significantly contribute to the ambitious decarbonization objective set by the European Green Deal of greenhouse gas emissions reduction of at least 50% by 2030 and environmental neutrality by 2050.this technology can play an important role in allowing high shares of solar PV and wind in the energy mix, thanks to its capability to provide dispatchable renewable heat/electricity
Efficient surface pre-treatments of stainless steel (SS) substrates were implemented and an Ag layer was placed between layers of W and W-aluminum nitride (AlN), characterized by higher compactness and homogeneity than those of W and WN-AlN of the double-nitride cermet technology previously developed by ENEA [26,28]
The multilayer structure of the optimized solar coating with improved thermal stability is composed of the following layers: SS/W/Ag/graded cermet (W-AlN)/antireflection filter (AR) filter (AlN, low Metallic Volume Fraction (MVF) cermet, SiO2 )

Summary

Introduction

Concentrating Solar Power (CSP) technology can be considered as a mature technology for large-scale renewable energy production [1,2], destined to significantly contribute to the ambitious decarbonization objective set by the European Green Deal of greenhouse gas emissions reduction of at least 50% by 2030 and environmental neutrality by 2050. This technology can play an important role in allowing high shares of solar PV and wind in the energy mix, thanks to its capability to provide dispatchable renewable heat/electricity. In linear focusing CST technology, two types of collectors are currently used: parabolic trough collector (PTC) and linear Fresnel collector (LFC) [5,6,7,8,9,10]

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