Proposal of a new parameter for the comprehensive qualification of solar mirrors for CSP applications

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Abstract

Hemispherical and near-specular solar reflectance are today the main parameters used in solar mirror characterization. Unfortunately they can not properly describe the mirror effectiveness in redirecting the Sun radiation towards a receiver in CSP applications because the reflectance concept is developed by assuming the impinging radiation travelling as a plane wave, like that emitted by an infinitely far point light source. Besides that, the measurement of the near-specular reflectance is so much difficult that slowed down the progress of the SolarPACES reflectance guidelines, still stopped at the 2013 version. The present paper launches a new idea in the ongoing discussion on solar-mirror qualification to work around these difficulties: solar mirrors could be better characterised by the new parameter named Sun Conic Reflectance (SRC), which represents the amount of solar radiation reflected at a point of the mirror, and intercepted by the receiver with acceptance-angle 2φR. The standard measurement of SCR requires the setting of two conditions about the solar radiation: spectrum and divergence. The first is ASTM G173-03, for the second here was chosen that of a perfect clear-sky day, when the Sun-disk surface is uniformly radiating, and viewed from the Earth under 9.46 mrad, but any other could be chosen if it can experimentally implementable. For φ < 4.73 = 9.46/2 mrad, SCR and near-specular solar reflectance behave very differently, because the first represents the solar radiation intercepted by the receiver, while the second refers to the reflection of impinging plane-waves, with solar spectrum, towards directions deviating from the specular one of less than φ. When φ ≥ 4.73 mrad, the difference is much lower, and becomes null when φ is large enough. The second advantage of SCR is that it can be directly measured by means a simple experimental set-up which schema is shown and discussed in the paper. The formulae for computing SCR from near-specular reflectance are also reported.
Original languageEnglish
DOIs
Publication statusPublished - 31 May 2016
Event21st International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2015 - Cape Town, South Africa
Duration: 31 May 2016 → …

Conference

Conference21st International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2015
CountrySouth Africa
CityCape Town
Period31/5/16 → …

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All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Cite this

Montecchi, M. (2016). Proposal of a new parameter for the comprehensive qualification of solar mirrors for CSP applications. Paper presented at 21st International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2015, Cape Town, South Africa. https://doi.org/10.1063/1.4949224