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Fresnel lens is a kind of lens that can concentrate sunlight up to a level of thousands of suns with small space occupation which is widely used in the research of sunlight concentration and transmission systems via optical fiber. Most studies on the concentrated flux of lenses use experimental methods to measure the flux distribution on the receiver of parabolic trough solar concentrators, solar power towers, and parabolic dish concentrators, while for Fresnel lenses, especially large-aperture Fresnel lenses such as the one in this manuscript, the simulation approach was mostly used. In response to this problem, this study has developed an experimental system for measuring the concentrated flux density of Fresnel lenses. A charge-coupled device (CCD) camera was used to capture the image of spot of large-aperture (968 mm) Fresnel lenses in the CCD camera-based method, and a heat flow meter was used to calibrate the spot brightness image obtained by the CCD camera. Experimental data show that the peak flux of concentrated spot can reach 4.06 MW/m2. This method confirms the simulation results of previous studies that using the rays tracing method, that is, the flux level of the Fresnel lenses can reach 5000 suns. The experimental results demonstrated 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.

Radiation from the circumsolar region called circumsolar radiation is part of direct solar radiation, but not all circumsolar radiation can be received by concentrating solar power (CSP). Circumsolar ratio (CSR) reflects the proportion of circumsolar normal irradiance in direct normal irradiance (DNI). CSR is related to the radial distribution of solar brightness (sunshape) and it is influenced by atmospheric turbidity and air mass (AM).Performance of CSP is affected by CSR, which should be considered in the CSP simulation and analysis. This work introduces a method of measuring CSR with a CCD camera and filters. Also a calculation method of DNI for different field of view based on the measured CSR is proposed.

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