Accelerated Aging Tests for Solar Absorber Coatings

Abstract

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.