Design of Fresnel Lens With Constant Height Spherical Facets

Abstract

In the present work, a ray tracing model based on Snell’s law of refraction is developed using MATLAB for the design of Fresnel lens with spherical facets of equal height. In practice, the facet curvature is approximated by straight line, which causes an increase in spherical aberrations and reduction in concentration ratio. The proposed model takes facet curvature into consideration, which will result in effective utilization of incident solar radiations. Fresnel lenses are available with facets having constant width and facets with constant height. A comparison of spherical aberrations in the two cases has also been presented using different f - numbers (ratio of focal length to aperture diameter). Effect of different parameters like number of facets and refractive index of lens material on concentration ratio is also presented in present study. The proposed ray tracing model is validated with the model developed in SolTrace, an open access software. The predictions from the proposed model are in good agreement with the results of SolTrace model with an average deviations of 6.8% for concentration ratio and 2.2% for focal length.