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- Aging of elastomeric components of a solar thermal collector under solar radiationPublication . Ferreira, Cristina; Ritto, G.; Cidade, M. T.; Carvalho, Maria João; Cunha Diamantino, TeresaABSTRACT: Elastomeric components play important functions in solar thermal collectors (STC’s) as sealings, fittings or absorbers, being important that they maintain their performance along STC lifetime. However, stress factors such as high temperatures and high levels of solar radiation, as exist in southern Europe countries, can affect the properties of those components. A testing programme for the assessment of elastomeric materials of such components is detailed in international standards (ISO 9808 and ISO 9553), which already considers the effect of heating.
- 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.
- Advanced cyclic accelerated aging testing of solar reflector materialsPublication . Wette, Johannes; Sutter, Florian; Tu, Mai; Fernández-Garcia, Aránzazu; Buendia, Francisco; Carvalho, Maria João; Cunha Diamantino, TeresaABSTRACT: Lifetime prediction methods for the components of concentrated solar power (CSP) plants have been in the focus of interest of manufacturers and plant developers for the past years. Recently, an accelerated aging standard for solar mirrors was published by the Spanish AENOR committee [1]. This standard allows performing comparative testing but it is not suited to derive meaningful life-time estimations. Firstly, the testing defined in the standard is not aggressive enough to produce significant degradation on most of the materials and secondly, it has been shown that the passing of these tests does not guarantee a high durability during outdoor exposure [2]. These findings have proven the need for the investigation of more realistic procedures. To provoke the mechanisms that are detected during outdoor exposure, a more realistic application of environmental stresses is being investigated. In this work a series of tests is conducted in which several weathering stresses are combined and applied in a cyclic manner. Some of these cycles have shown to correlate better with real outdoor behavior.