Accelerated aging tests to selective solar absorber coatings for low temperature applications

• Published in: Solar energy materials and solar cells 2021-10, Vol.232, p.111320, Article 111320
• Main Authors: Diamantino, Teresa C., Gonçalves, Rita, Páscoa, Soraia, Alves, Isabel N., Carvalho, M. João
• Format: Article
• Language: English
• Subjects: Accelerated aging test; Accelerated aging tests; Accumulators; Aging; Atmospheric corrosion; Chlorides; Coatings; Component reliability; Contaminants; Corrosion; Drying; Durability; Durability test; Environmental stress; Gases; Humidity; International standards; Low temperature; Materials; Nitrogen dioxide; Nitrogen oxides; Outdoor exposure; Photochemicals; Physical vapor deposition; Selective solar absorber coatings; Selective surfaces; Solar absorver surfaces; Solar collectors; Solar energy; Solar energy absorbers; Solar heating; Solar thermal collectors; Spraying; Stress corrosion; Sulfur; Sulfur dioxide; Wetting
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2021.111320

The need of a higher role of solar energy within the energy mix in the coming decades obliges the collectors to increase their performance and reliability. It is demanded that the solar absorbers, as the key component of solar thermal collectors, should be low cost with high efficiency for extended lifetimes under different kinds of environments. Commercially, there are presently two main types of solutions as selective solar absorbers coatings for low temperature applications: coatings obtained by physical vapour deposition (PVD) and by paint coatings (PC). These coatings present different physical and chemical characteristics. Therefore, it is important to know how these commercial coatings degrade over time in different environments. Results obtained with two different PVD coatings and three PC, under different accelerated aging tests, are presented. The aging tests performed included different environmental stress corrosion conditions: temperature, humidity, chlorides, sulfur dioxide and nitrogen oxides. The chlorides and the gases SO2 and NO2 affect distinctly the different selective coatings. Cyclic variation of corrosion promoting gases (sulfur dioxide and nitrogen dioxide), higher humidity, salt spraying and drying seem to be an aging test that reflects the different environments where the solar thermal collectors are exposed. In addition to the contaminants, drying/wetting cycles also play an important role in degradation mechanisms of absorber coatings. So, the international standard ISO 22975-3 needs to be revised to include cyclic conditions with these contaminants. [Display omitted] •Selective solar absorber coatings were ranked the same way in accelerated tests and in outdoor exposure.•Synergistic or inhibitory effects between environmental agents are crucial in the degradation of selective coatings.•Degradation depends on the absorber coating and the damaging agent.•AAT involving cyclic conditions of neutral salt spray, pollutant gases and TDW show good correlation with outdoor exposure.•The standard ISO 22975-3 need to be revised to include accelerated aging test to include the main damaging agents that STC are subject.