Abstract:
A Standard-Compound Parabolic Concentrator (S-CPC) has been used to collect and/or concentrate the solar radiation from the solar over a relatively wide range of angles. Once the S-CPC has been placed along the east-west direction in the northern hemisphere towards the north, where the solar rays irradiate from the south side, the south-facing panels cannot effectively concentrate to intercept the light directly to the surface of the absorber throughout the year. Particularly, the southern side of the non-concentrating surface absorbs the solar radiation energy after the temperature rises, resulting in the increasing thermal stress for the material aging, where the face shape structure can be more easily damaged. In this study, a novel mathematical model was constructed for the face structure of a Shell-Shape Compound Parabolic Concentrator (SS-CPC) with a circular absorber, according to the non-imaging optical fringe light. The partial light interception by the southern face of the S-CPC was effectively eliminated to run smoothly during the daylight hours from the autumn equinox to the following spring equinox. Meanwhile, a physical prototype of SS-CPC was also fabricated using 3D printing. A visible laser experimental device was then selected to verify the concentrating characteristics. It was found that the light paths from the numerical simulation and experimental measurement were better consistent within a certain difference range, indicating the high accuracy of the theoretically constructed SS-CPC surface structure. Four SS-CPCs were prepared with different rotation angles β (0°, 7°, 34°, and 44°) in the Kunming City, Yunnan Province, southern China at 25°N. The optical performance was determined to compare with the S-CPC with the same acceptable half-angle. The results were as follows. 1) The rotation angle β was negatively correlated with the overall optical efficiency of the SS-CPC. There was a slow decrease and then a gradual increase in the optical efficiency of the SS-CPC within the full incidence angle, with the increase of the incidence angle of the sunlight. The optical efficiency decreased significantly after exceeding the maximum receiving angle θa, but still maintained above 0.1, until the sunlight cannot be received on the surface of the concentrator. The average optical efficiencies of SS-CPC were 0.639 8, 0.635 2, 0.620 1, and 0.609 3 for the four β values, which were much higher than that of S-CPC (0.567 6). 2) The aperture width L of SS-CPC increased gradually, but then decreased at the critical, as the projected incidence angle θp of solar rays increased. The aperture L also increased gradually, as the rotation angle β increased. As such, there was a significant effect on the light-harvesting volume of SS-CPC. 3) The uniformity index of energy flux distribution on the surface of SS-CPC absorber also increased, with the increase of β values within the maximum acceptable angle. Once exceeding that, there was a negative correlation between the β value and uniformity index. The uniformity index of energy flux distribution in the SS-CPC with the four different β values were 0.169 2, 0.193 0, 0.171 9, and 0.184 2, respectively, which were much smaller than that of S-CPC (0.204 0), when θp was 20°. Nevertheless, the uniformity index of energy flux distribution in the SS-CPC was much larger than that of S-CPC for the other projection angles. Consequently, the SS-CPC increased the width of the effective aperture, compared with S-CPC, thereby effectively avoiding the failure to concentrate the light caused by the intercepting solar rays on the southern face of S-CPC. This finding can also provide a strong reference for the utilization of solar radiation and the cost-saving consumables during photovoltaic concentrator manufacturing.