Solar mirror qualification setup, the key instrument in a new strategy for evaluating off-normal near-specular solar-reflectance.

Solar reflectance is one of the most important parameters characterizing the mirrors used to redirect the solar radiation toward a receiver in concentrating solar power plants. In Solar Power and Chemical Energy Systems (SolarPACES) Task III, an international group of experts is drafting the reflectance guidelines and debating the hard task of measuring off-normal near-specular solar-reflectance. Because of the lack of suitable commercial instruments, several research institutes are studying and setting up special equipment. Since 2012, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) proposed an articulated strategy based on modeling the hemispherical spectral reflectance with the equivalent model algorithm and the ratio of near-specular to hemispherical reflectance with the total integral scattering equation; in the latter, the roughness is replaced by the heuristic parameter σ φ , nonphysically dependent on the acceptance angle. The solar mirror qualification experimental setup was conceived for measuring σ φ . Recently, SolarPACES approved a new project to support the working group for improving the proposed instruments. The paper summarizes the ENEA strategy and presents the latest version of the instrument, SMQ2, discussing its several important new features: self-calibration, setup simplification, straightforward applicability to high specular mirrors, measurement-time cutoff, and acceptance-angle range extended up to 50 mrad.