Abstract
The goal of this presented study was to determine the optimum parameters of secondary optical elements (SOEs) for concentrated photovoltaic (CPV) units with flat Fresnel lenses. Three types of SOEs are under consideration in the design process, including kaleidoscope with equal optical path design (KOD), kaleidoscope with flat top surface (KFTS), and open-truncated tetrahedral pyramid with specular walls (SP). The function of using a SOE with a Fresnel lens in a CPV unit is to achieve high optical efficiency, low sensitivity to the sun tracking error, and improved uniformity of irradiance distribution on the solar cell. Ray tracing technique was developed to simulate the optical characteristics of the CPV unit with various design parameters of each type of SOE. Finally, an optimum KOD-type SOE was determined by parametric design process. The resulting optical performance of the CPV unit with the optimum SOE was evaluated in both single-wavelength and broadband simulation of solar spectrum.
Highlights
A concentrated photovoltaic (CPV) unit is generally composed of a primary optical element (POE), a secondary optical element (SOE) and a solar cell
Three types of SOEs were evaluated in the preliminary design process, including (1) kaleidoscope with equal optical path design (KOD); (2) kaleidoscope with flat top surface (KFTS); and (3) open-truncated tetrahedral pyramid with specular walls (SP)
When the incidence angle is smaller than 1.2°, most of the incident rays refracted from the POE will be refracted at the top elliptical surface of the KOD-type SOE and be reflected at the bottom surface to the solar cell
Summary
A concentrated photovoltaic (CPV) unit is generally composed of a primary optical element (POE), a secondary optical element (SOE) and a solar cell. Using a SOE with a Fresnel lens in a CPV unit will achieve high optical efficiency, lower the sensitivity to the sun tracking error, and improve the uniformity of irradiance distribution on a solar cell [8,9,10]. The three major factors used in evaluating a CPV system include the optical efficiency, the acceptance angle and the uniformity of irradiance distribution on the solar cell. The optical efficiency of a photovoltaic system is defined as the ratio of the radiant flux on the solar cell and the POE surface. Optical characteristics of the CPV unit with the optimum SOE were evaluated in broadband solar spectrum in the range of 400–1300 nm
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