Investigation Of Photothermal Performance Of Solar Compound Parabolic Concentrator

In the medium-low temperature solar applications,the solar compound parabolic concentrator has the advantages of low requirement for tracking accuracy and receiving part of scattered light.However,it’s concentrating performance is greatly affected by the incidence angle,and the total daily output energy fluctuates greatly.Therefore,a new type solar compound parabolic concentrator is designed in this paper through adding double-sided undersurface of the glass cover plate,which can recieve the light without photothermal conversion and realize photoelectric conversion,and improve the overall ray’s receiving rate and solar energy utilization efficiency of concentrator.When the concentrator works in winter,the glass cover can also be defrosted by using hot air generated by Photovoltaic modules,so it can realize the efficient coupling of photothermal photoelectric conversion process in ’ inner concentrating ’ solar capture device.Firstly,based on the composed equation of the new type solar compound parabolic concentrator,the 3D model is established and imported into the optical simulation software Trace Pro.Theoretical comparative analysis of the overall ray’s receiving rate,light escaping rate and heat collecting efficiency on new type solar compound parabolic concentrator and the traditional solar compound parabolic concentrator,and the number of light on cylindrical receiver and Photovoltaic modules surface are calculated.The results indicate that when the incidence angle is 12°,the overall ray’s receiving rate of the new type solar compound parabolic concentrator is 97.5 %,which is 62.13 % higher than that of the traditional solar compound parabolic concentrator.Based on the laws of thermodynamics,the steady-state heat transfer model of the new type solar compound parabolic concentrator is established.Based on this,a new type solar compound parabolic concentrator performance testing bench is built.Under the actual weather conditions,the effects of solar irradiance,ambient temperature,receiver shape and air flow rate on the temperature of inlet and outlet,the air temperat.in cavity,glass cover temperature,instantaneous heating collection,back temperature of Photovoltaic modules and output power of concentrator are tested,and the influence mechanism of incidence angle on the discrepancy between the inlet air temperature and outlet of the concentrator,the output power and the back temperature of the Photovoltaic modules was analyzed,then the thermal performance such as the discrepancy between the inlet air temperature and outlet of the concentrator operated in cloudy days was comparatively studied.The results show that when the air flow rate is 2.87 m/s,the maximum instantaneous heat collection,average photothermal conversion efficiency and photothermal-photoelectricity comprehensive efficiency of the concentrator with “mi” shaped reciever are 427 W,77.27 % and 77.72 %,respectively,which are 37 W,14.47 % and 9.51 % higher than that of the concentrator with mesh receiver.When the concentrator is running at noon and the incidence angle is 0°,the maximum discrepancy between the inlet air temperature and outlet and the instantaneous heat collection of the concentrator are 14.25 °C and 427 W,respectively,which are 7.1 °C and 201 W higher than that when the incidence angle is 10°.When the concentrator operates in winter,the new type solar compound parabolic concentrator has the function of “self-defrosting”.By changing the relative height of the back of the plate installed at the light inlet of the concentrator relative to the Photovoltaic modules,an air flow channel is formed along the oblique direction of the glass cover plate.When the obliquely incident solar light enters the concentrator,it is first absorbed by the Photovoltaic modules.The hot air generated in the photoelectric conversion process can defrost the surface of the glass cover plate,shorten the startup time of the concentrator,and improve the daily output heat collection of the concentrator.In order to facilitate the quantitative description of the defrosting ability of the concentrator,the defrosting rate is proposed.The results show that on the test day,when the ambient temperat.is-6 °C,the maximum temperature of the glass cover plate of the concentrator is about 10 °C,and the defrosting rate is 20.34 g/h.The defrosting of the glass cover plate is realized before the incident sunlight is received by the embedded receiver in the single glass tube.