Commercial first-surface solar-mirrors, which are alternatives to conventional glass mirrors, reflect solar radiation in a broader manner because of light scattering. However, in concentrated solar power all the radiation reflected in the solid angle of receiver-viewing is useful. This makes a mirror-evaluation methodology which takes into account not only specular, but also near-specular reflectance, mandatory. Two laminated mirrors and one traditional were analysed with a new method based on near-normal incidence reflectance measurements of the hemispherical spectrum, and near-specular at 405.5, 543.5 and 632.8. nm, for several acceptance angles. For a given acceptance angle, the wavelength-behaviour of the ratio near-specular/hemispherical is found well modelled by the well-known Total Integrated Scattering relationship. The angular-behaviour of the hemispherical reflectance is predicted by a simplified optical model of the mirror. As final result, the behaviour of solar reflectance versus the incidence-angle over the investigated acceptance-angle range was obtained. © 2013 Elsevier Ltd.

Approximated method for modelling hemispherical reflectance and evaluating near-specular reflectance of CSP mirrors

Montecchi, M.
2013

Abstract

Commercial first-surface solar-mirrors, which are alternatives to conventional glass mirrors, reflect solar radiation in a broader manner because of light scattering. However, in concentrated solar power all the radiation reflected in the solid angle of receiver-viewing is useful. This makes a mirror-evaluation methodology which takes into account not only specular, but also near-specular reflectance, mandatory. Two laminated mirrors and one traditional were analysed with a new method based on near-normal incidence reflectance measurements of the hemispherical spectrum, and near-specular at 405.5, 543.5 and 632.8. nm, for several acceptance angles. For a given acceptance angle, the wavelength-behaviour of the ratio near-specular/hemispherical is found well modelled by the well-known Total Integrated Scattering relationship. The angular-behaviour of the hemispherical reflectance is predicted by a simplified optical model of the mirror. As final result, the behaviour of solar reflectance versus the incidence-angle over the investigated acceptance-angle range was obtained. © 2013 Elsevier Ltd.
Reflectance;Hemispherical;Off-normal;Mirror;Near-specular;CSP
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.12079/663
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