Optical damage tests on reflecting materials for solar applications using concentrated sunlight

Year: 2014

Authors: Coraggia S., Fontani D., Jafrancesco D., Sansoni P., Francini F., Mercatelli L., Sani E., Meucci M., Marconi L.

Autors Affiliation: CNR-INO Istituto Nazionale di Ottica, Largo E. Fermi 6, 50125 – Firenze

Abstract: Concentrated Solar Power (CSP) and Concentrating Photovoltaics (CPV) usually involve secondary optics (lenses or mirrors) in order to improve system energetic performances. These secondary elements should collect the sunlight concentrated by the primary optic. Therefore, the materials suitable for the realization of secondary concentrators must withstand a long-time exposure to solar high power densities without significant decay of their optical performances. An accurate optical characterization of these materials should include an investigation on their degree of resistance to high-power light, by means of exposing them to concentrated sunlight for several hours in monitored conditions. This paper presents the optical study on three samples of two different materials, which are possible candidate for the construction of secondary reflectors for a solar furnace. The goals of this study were to test the samples endurance at the working power density, verifying if an achievable damage threshold exists and eventually correlating it with some measurable parameters like exposure time or temperature. In synthesis the tests were of two types: field tests with sun exposure and laboratory optical characterization. The field test consisted in exposing the samples (named A, B and C) to sunlight by using a dual-axis solar tracker and a suitable Fresnel lens. Samples A and B were sections of the same glass mirror. Sample C was a multilayer mirror based on an aluminum substrate. The measured parameters were: Temperature of the back side of the sample; solar power density concentrated on the sample; exposure time. The optical characterization involved measurements of reflectance, regularly performed to check variations in the optical features. Only sample B suffered a structural failure at the end of the exposure period, and this involved only the glass cover; none of the samples showed appreciable decays in reflectance during the whole exposure period.

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KeyWords: Materials; Solar concentration; Solar tests
DOI: 10.1016/j.egypro.2014.10.318

Citations: 1
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