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- Accelerated aging tests to selective solar absorber coatings for low temperature applicationsPublication . Cunha Diamantino, Teresa; Gonçalves, Rita; Páscoa, Soraia; Alves, Isabel Nascimento; Carvalho, Maria JoãoABSTRACT: 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.
- Accelerated aging tests for solar absorber coatingsPublication . Cunha Diamantino, Teresa; Gonçalves, Rita; Páscoa, Soraia; Alves, Isabel Nascimento; Chambino, Teresa; Ferreira, Cristina; Carvalho, Maria JoãoABSTRACT: The need of a higher role of solar energy within the energy mix in the coming decades obliges the systems to increase their performance and reliability. It is demanded that the solar absorbers, as the key component of solar thermal systems, should be low cost with high efficiency for extended lifetimes under different kinds of environments. Commercially, there are two different types of solutions as selective solar absorbers coatings: coatings obtained by physical vapor deposition (PVD) and by paint coatings (PC). These coatings present different physical and chemical characteristics. Therefore, it is important to know how these 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, sulphur dioxide and nitrogen oxides. 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.
- Coletores solares térmicos : evolução do comportamento térmico após diferentes períodos de exposição em ambientes com distintas corrosividadesPublication . Carvalho, Maria João; Páscoa, Soraia; Mexa, Nuno; Gonçalves, Rita; Correia, J.; Gano, António; Cunha Diamantino, TeresaRESUMO: Os coletores solares térmicos devem estar preparados para suportar condições ambientais adversas, como temperatura, humidade e irradiância ultravioleta elevada ou cargas de vento e neve, mas também outras influências, como os níveis de contaminantes como cloretos, dióxido de enxofre e óxidos de azoto, dependendo da localização geográfica. Num trabalho que se desenvolve desde 2012, têm sido estudados os efeitos destes contaminantes existentes no ambiente exterior e a sua penetração no interior dos coletores, assim como a evolução do comportamento térmico dos coletores quando expostos por períodos prolongados em ambientes com diferentes corrosividades. Neste trabalho apresentam-se os resultados para um período de três e cinco anos em dois locais com distintas corrosividades, Sines e Lisboa, observando-se que locais como Sines com um ambiente marítimo industrial tem impacto no comportamento térmico dos coletores expostos.
- The importance of developing accelerated tests on the reliability of solar absorber and solar reflector coatingsPublication . Cunha Diamantino, Teresa; Gonçalves, Rita; Páscoa, Soraia; Alves, Isabel N.; Carvalho, Maria João; Fernández-García, Aránzazu; Wette, Johannes; Sutter, FlorianABSTRACT: Selective absorber coatings for solar thermal collectors and reflector coatings for Concentrating Solar Power (CSP) plants are the key components of these technologies and their durability is one of their most important characteristics. They should be low cost and withstand 20-30 years under different kinds of environments without significant loss of optical performance. Commercially, there are different physical vapour deposition (PVD) coatings for aluminium absorbers and reflectors. Results obtained with two commercial PVD solar absorber coatings (SA) and two solar reflector coatings (SR), under different accelerated aging tests (AAT), are presented and correlated with outdoor exposure. An Outdoor Exposure Testing (OET) site with maritime and industrial influence was used for an exposure campaign of the absorbers and reflectors for two years. Alternative artificial aging tests are proposed for absorbers and reflectors that better reproduce the corrosion mechanism obtained in natural conditions with maritime and industrial influence. The characterization of the coatings and degradation mechanisms of different aluminium absorbers and reflectors were evaluated optically, morphologically and chemically. The results obtained in an atmosphere with high corrosivity as in marine and/or industrial areas are a reliable way to verify the corrosion resistance of new materials in a short time and are a valuable tool to validate the different methodologies of accelerated aging tests.