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25 November 1992 Silvered low-iron glass: experience and new developments
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Glass is a well established material in the area of solar reflectors for the excellent match between its basic properties and the requirements for such applications. When using 4 mm glass with low iron content in combination with silver as a reflecting layer and the appropriate protection layers to guarantee its environmental stability, the initial reflectance of 94% (averaged over the solar spectrum) can be maintained during its useful life even under harsh conditions as they are prevalent in such applications. The FLACHGLAS Group has manufactured solar reflectors since 1978 and the accumulated output exceeds 2 million m2. This paper gives information about the experience gained during the past decade in terms of optical performance, soiling and cleaning history, and overall durability of the mirrors. When using glass as a reflector material, the mirror is also an important structural element of the solar collector as a whole and this paper, therefore, gives some basic design considerations. Using examples from other fields where glass is used for structural elements it shows that the mechanical performance of glass is often underestimated. Most of the reflector surface operating in solar applications today serves to concentrate the incident solar radiation onto heat collecting elements. Optical quality is then described by the solar averaged reflectivity and the image quality via the contour accuracy of the formed mirror. The solar R&D community has currently put an emphasis on `Solar Chemistry.' Here, an additional specification for solar concentrators is a high reflectance in the UV-range of wavelengths, which conventional silver reflectors cannot render. The paper describes a recent development of a durable glass mirror with enhanced UV-reflectance while maintaining a solar averaged reflectance of over 94%.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ingo Susemihl and A. Dauwalter "Silvered low-iron glass: experience and new developments", Proc. SPIE 1727, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XI: Selective Materials, Concentrators and Reflectors, Transparent Insulation and Superwindows, (25 November 1992);


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