Calculation of the incidence angle modifier of a Linear Fresnel Collector: The proposed declination and zenith angle model compared to the biaxial factored approach

Abstract

Since their first appearance as a contribution by Professor Francia at the University of Genova, Italy, the Linear Fresnel Collectors (LFC) demonstrated to be an engineering efficient technology for medium to high temperature solar applications. The strength of the LFC concept is related to the simple mirror motion law, to the compactness of the mirror fields (power to land surface ratios), to the lowest resistance to wind, to the system intrinsic scalability. To perform reliable LCOE analyses, robust performance simulation tools are needed. The Authors developed to this aim a 3D ray-tracing model, able to account for shading, blocking, and end effects as a function of LFC geometry, including primary and secondary mirror curvatures. In this paper, a new approach is implemented to reduce huge yearly ray-tracing datasets and provide very compact analytical equations for fast hourly performance simulations. The present model introduces new Incidence Angle Modifier (IAM) correlations based on the declination and zenith angles. The new model demonstrated to fit subhourly 3D ray-tracing data all year long with an overall error lower than 1.5%, well below the best IAM factored models here compared as a general criticism to the biaxial factored approach related to Fresnel applications.