A Survey of Selective Solar Absorbers and Their Limitations
نویسندگان
چکیده
A number of mater ia ls and techniques have been used t o form se lec t ive s o l a r absorber coatings. Each of the coating processes and the coatings formed has i t s own l imi ta t ions which a r e generally paorly defined. The poor s t a t e of knowledge on the l i m i t a t i o n s of the coating processes and the resu l t ing coatings poses a problem f o r the component design and the mater ia ls engineer. This paper reviews the s t a t e of knowledge of 9 of the coating processes and mater ia ls being used and of po ten t i a l usefulness i n mid-temperature solar-thermal co l l ec to r s . A p r inc ip le point t h a t is made i s the lack of production experience and knowledge of the degradation modes f o r most of the coating technologies and coat ing material . 1. 1nZrroduction.Solar r ad ia t ion is a low i n t e n s i t y energy source whose u t i l i z a t i o n requires e f f e c t i v e co l l ec t ion and re ten t ion t o beeconomically feas ib le . Operational temperature ranges of so la r co l l ec to r systems may be categorized as : low-temperature (T < 100°C), mid-temperature (100 < T < 400°C), and high-temverature (T > 400°C) . To obtain mid and high opera t ional temperatures, some degree of concentration of the incident r ad ia t ion is required /l/. In the mid-temperature range, the concentration ( r a t i o of aper ture area t o receiver area) w i l l gener a l l y be from 5 t o 50 while i n the high-temperature co l l ec to r s the concentra t ion may exceed 1000. Collector designs u t i l i z e a receiver surface t o absorb the inci dent s o l a r radia t ion /l/. In the "coating receiver1', the rad ia t ion i s absorbed i n a coating o r surface layer and the heat i s conducted through the container wall t o the heat t r a n s f e r media. In the "container receiver" , the rad ia t ion is absorbed within the cont a i n e r walls while the " f l u i d receiver" , the rad ia t ion is absorbed i n (U) This work i s supported by the U . S . Department of Energy under Cont r a c t DE-AC04-76-DP00789. (W) A U.S. DOE f a c i l i t y . Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981102
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