Design and fabrication of concentrated photovoltaic optics with high numerical aperture using a curved catadioptric optical system

We developed an optical system for a concentrated photovoltaic system composed of primary and secondary optical elements designed to reduce the thickness of the module and minimize the optical loss. The Primary optical element (POE) was designed as a catadioptric Fresnel lens with an annular stepped structure to reduce the focal distance and optical loss. To introduce light rays focused by the POE at large exit angles to the surface of a solar cell with a homogeneous intensity distribution, the Secondary optical element (SOE) was designed with a total internal reflection surface. Each of the optical elements was fabricated and assembled, and the optical efficiency of the system and the photoelectric transformation efficiency were evaluated in indoor and outdoor tests, respectively. The optical efficiency of the module was ~80%, with an acceptance angle of ± 0.6°. A photoelectric transformation efficiency of 30.75%, based on the peak value, was measured through outdoor current-voltage measurements.