Specularity of concentrator mirrors for CPV measured with VLABS

Abstract

We investigate the specular reflectance properties of four different mirror samples suitable for mass-manufacturing of CPV primary concentrators. The laboratory setup VLABS and its data evaluation procedure to calculate specular reflectance are introduced. We present measurement results of specular reflectance with a very high angular resolution around the specular direction making it possible to compare different mirror materials to a high degree of accuracy for arbitrary acceptance angles. It is shown that the specular reflectance can be significantly lower than hemispherical reflectance due to surface scattering. For a CPV system with 1° acceptance angle the loss of radiant flux due to surface scattering amounts to a maximum of 8% relative for the investigated samples.