Measurement Of The Highly Concentrated Solar Flux Of Large Fresnel Lens

A Fresnel lens is a type of lens that can concentrate sunlight up to thousands of times with minimal space occupancy,and it is widely used in the research of sunlight concentration and transmission systems via optical fiber.While most studies on the concentrated flux of lenses rely on experimental methods to measure the flux distribution on the receiver of parabolic trough solar concentrator,solar power tower,and parabolic dish concentrators,simulation approaches are typically employed for Fresnel lenses,especially for large-aperture ones,as in this manuscript.To address this issue,this study developed an experimental system for measuring the concentrated flux density of Fresnel lenses.The present paper explores the measurement and calculation of the concentrated flux of a large-aperture Fresnel lens,both theoretically and experimentally.First,we provide a detailed introduction to different scenarios,including the CCD camera method,the heat flow meter method,and the simulation simulation method.For the hardware scenario required in this paper,a large Fresnel concentrated flux measurement system is built,which includes a manual two-axis tracking system,a focusing system(large-aperture Fresnel lens and shelters),and a measurement system(heat flow meter,CCD camera).In the CCD Camera-based method,a charge-coupled device(CCD)camera is used to capture the spot image of large-aperture(968 mm)Fresnel lenses,while a heat flow meter is used to calibrate the spot brightness image obtained by the CCD camera.Additionally,an infrared thermal imager is used to observe the temperature field information of the focused spot in the experiments.Our study proposes a measurement system based on the CCD camera method,which can measure the high-level concentrated flux and obtain the flux density distribution by combining it with information such as the direct normal irradiance(DNI)of the sun.The experimental data show that the peak flux of the concentrated spot can reach 4.06 M W/m2.This method confirms the simulation results of previous studies that used the rays tracing method,demonstrating that the flux level of the Fresnel lenses can reach 5000 suns.Our experimental results demonstrate that the CCD camera-based method,combined with a heat flow meter,is competent in measuring the intensity of flux with a level of 5000 suns.