Design And Analysis Of A Multi- Ring Fresnel Heliostat

In tower solar thermal power generation systems,the cost of heliostats is huge,accounting for about 40% to 50%.In order to ensure the optical performance of heliostats and further reduce the cost,based on the research progress of heliostats,this paper proposes a construction method of multi-circle Fresnel heliostats composed of plane sub-mirrors.This paper mainly carries out theoretical analysis and exploration from the following aspects:By analyzing the parameters of traditional heliostats,combined with an umbrella mechanical structure,a heliostat model of a single-turn Fresnel surface was established.The optical performance of the heliostat was analyzed by the optical simulation of TracePro.The mechanical design of the prototype was completed by using 3D modeling of CAD.The concentrating experiment was carried out in Nanjing.In order to further improve the optical performance and reduce the cost of sub-mirrors,a multi-turn Fresnel heliostat model was established using Solidworks.The results show it can make the mirror mirrors have a small gap ratio and reduce the sub-segment.The smaller the sub-mirror size,the higher the geometric concentration ratio,and the increased number of submirrors,resulting in an increase in the corresponding support structure and an increase in the cost of the support and position adjustment device.In order to determine the optimal tilt angle of the heliostats under different working conditions,a set of algorithms for calculating the tilt angle is proposed by geometric analysis.it is found that the size of the focal spot formed make the energy density of the heat absorption surface more uniform.the difference between Fresnel heliostat and ideal spherical heliostat at the optimal tilt angle is compared.The results show that the focal spot size of Fresnel heliostat changes more slowly with the incident angle.Analyze the influencing factors of the optimal tilt angle.The results showthe value of the optimal tilt angle is almost independent of the design incident angle,;the closer the heliostat is to the heat absorbing surface,the lower the accuracy of the tilt angle.The influencing factors of the focal spot size of heliostats are studied.The results show that the focal spot size of heliostats increases with the increase of incident angle.After the incident angle is greater than 30°,the growth rate is sharp,below 20 ° The growth rate is slow;the focal spot size of the heliostat depends mainly on the focal spot size formed by the outermost mirror,so the accuracy of the tilt angle of the outermost mirror is higher,and the tilt angle of the other inner mirrors can fluctuate.The scope,the accuracy requirements are lower,and the installation and debugging is more convenient and quick.