Optical Characterization of a New Facility for Materials Testing under Concentrated Wavelength-Filtered Solar Radiation Fluxes

Abstract

The materials used to manufacture solar receivers for tower power plants must withstand high fluxes of concentrated solar radiation (from 0.1 to even 1.5 MWm−2) and operate at high operating temperatures (>800 °C). Durability is a key aspect in these systems, which must be ensured under these demanding operating conditions, which also include daily heating–cooling cycles throughout the lifetime of these power plants. So far, to the authors’ knowledge, which wavelengths of concentrated solar radiation have the greatest influence on the mechanisms and speed of aging of materials used in solar receivers has not been analyzed. Yet, such an analysis is pertinent in order to implement strategies that delay or inhibit such phenomena, and, thus, increase the durability of central tower systems’ receivers. To perform such analyses, a new solar furnace was recently designed and installed at the Plataforma de Almería (Spain). This paper describes the components of this new solar furnace. The components are as follows: a heliostat to redirect the direct solar radiation towards a Fresnel lens that concentrates the solar radiation on the material under study, a shutter that allows varying the amount of concentrated solar radiation incident on the Fresnel lens, and reflective filters with selective reflectance that are placed between the Fresnel lens and the material. This paper also describes the procedure and the first results of the energetic and spectral characterization of this new solar furnace. The first experimental results of the characterization of this new test bed using the heliostat and the Fresnel lens showed that concentration ratios of up to 1000 suns (1 sun = 1000 Wm−2) could be achieved. Furthermore, the paper presents the results of the spectral characterization of the test system, using selective reflectance mirrors in the near-visible–IR wavelength range (400–1125 nm) and in the visible–IR red region (700–2500 nm).