On-site optical control for solar mirrors

Surface profile control on heliostats is crucial because the mirror surface can be imperfectly manufactured, and the distribution of solar irradiance on the receiver is sensitive to the slope of the heliostat surface. In practice heliostat surface irregularities introduce aberrations that contribute to enlarge the spot on the receiver and the resulting energetic losses depend on the collection characteristics of the solar plant. Since the solar field can be formed by thousands of mirrors, it is indispensable to have a method of rapid and economic control to be used during the operations of fabrication and successively also on the field during installation. The proposed method is based on techniques of structured light and assesses the heliostat surface quality by means of the inspection of a colored pattern image. This on-site optical control was applied on various mirror types, adapting the colored pattern. The method application requires only a photographic camera and a screen with heliostat sizes. Mirror surface defects appear as deformations in the pattern image. The main advantages are facility of application, low-cost equipment, elaboration simplicity.