Design of a double-sided Fresnel lens for compact concentration photovoltaics systems

Fresnel lenses have become the mostly used concentrator in concentration photovoltaics (CPV) due to its thinness and high concentration. Typical Fresnel lens design principle requires the focal length much greater than its diameter, posing potential spatial confinement to CPV configuration. In this paper, a CPV with concentration ratio of 245 at 3.5 mm from the center of the lens is designed, featured with a double-sided circular Fresnel lens (20 × 20). For traditional PMMAbased Fresnel lens, a long focal-length is required to avoid the concentration efficiency loss on the edge of the grooves due to total reflection. To overcome the limitation, a theoretical model of double-sided Fresnel lens is proposed. In this model, groove parameters of the rear surface are carefully tuned to pair the refracted light from the front surface in order to achieve desired ray deviation. Uniform radiation and an angle tolerance for incline illumination of 6 degrees is also taken into account to ensure the overall performance of the concentrator. The design shortens the axial working distance between the concentrator and the photovoltaic cell, in order to create a more compact CPV module or satisfy some spatial-confined CPV applications.