Performance Research On Trough Solar Compound Parabolic Concentrating System

The shortage of fossil energy and the environment pollution caused by the utilization of fossil energy have been one of the most serious challenges in the modern human society.It is urgent to find a kind of clean renewable energy which may relieve or even replace fossil energy.Solar energy is regarded as one of the most promising renewable energy because of its huge amount,wide distribution and convenient access.However,it also has some disadvantages,such as low energy flow density,uneven spatial distribution and discontinuous sunshine time,so it is necessary to concentrate solar radiation by solar concentrator collector in order to achieve the purpose of efficient utilization of solar energy.Although the high temperature that the point or line focusing collector could be achieved,the requirement for tracking accuracy increases the construction,operation and maintenance cost of solar energy collection system,which is not conducive to the promotion of marketization.Therefore,this paper designs a kind of Compound Parabolic Concentrator,which is suitable for low and medium temperature thermal applications,with large receiving half angle and low requirement for tracking accuracy.The research on it is carried out as follows:The parabola equation of the concentrator is obtained,also the relationship between the acceptance half angle and height-width ratio of the concentrator is given.The 3D model of the concentrator is established by SolidWorks software.The effects of the receiver position,ray incident angle and solar height angle tracking error on the performance of the concentrator are simulated and studied by the optical simulation software.The results show that,the ray receiving rate and efficiency of the CPC increase first and then decrease with the increase of the distance between the receiver and the bottom of the CPC,and there is an optimal focusing position for receiver under a given size.With the increase of ray incidence angle and solar azimuth tracking error,the ray receiving rate and concentrating efficiency of the concentrator decrease.The ray receiving rate of the receiver surface is still up to 75.87% when the ray incidence angle increases to 8 °.The solar azimuth tracking error has a greater effect on the performance of the concentrator.When the solar azimuth tracking error is 8 °,the ray receiving rate of the concentrator is only 35.31%.According to the CPC model designed,an object of the concentrator is obtained by mechanical design and machining process,and based on the results of optical simulation,a testing system for the photo-thermal performance of the concentrator is built in Hohhot.Under the actual weather conditions,the effects of the installation angle of the concentrator,the solar radiation,the mass flow rate of the medium and the cover plate on the performance of the concentrator when the heat conduction heat transfer medium of oil or air are studied in correlation experiments.It is obtained that when the inlet oil temperature of the oil is the same,the outlet oil temperature of normal incidence is about 3 ℃ higher than that of outlet oil with incident angle tracking error of 10 °.The photo-thermal conversion efficiency of the CPC increases with the decrease of mass flow rate of heat conduction oil,and when the mass flow rate is 100 kg/h,the instantaneous photo-thermal conversion efficiency of normal incident CPC is 65.04%.The temperature difference between inlet and outlet of the concentrator decreases with the increase of air velocity,under the actual operating conditions,and the maximum temperature difference between the inlet and the outlet of the concentrator with an inclination angle of 55 ° can reach 9.4 ℃,which is about 2.5 ℃ higher than that with an inclination angle of 10 ° at the same time.The glass cover plate has a great influence on the thermal performance of the concentrator.The maximum temperature difference between the inlet and the outlet of the concentrator with the cover plate is up to 11.3 ℃,which is 7.9 ℃ higher than that of the concentrator without the cover plate at the same time.The maximum efficiency of the cover plate concentrator is 55% at noon,which is 1.53 times of the maximum efficiency of the concentrator without cover plate.Finally,in order to further increase the acceptance angle of the CPC and reduce the tracking accuracy requirement of the concentrator,based on the original CPC and the target parameters.The parabolas that formed the concentrator are obtained by rotating and translating the original parabolas.A non-imaging CPC with height-width ratio of about 1 and concentration ratio of about 2,meanwhile parabola’s focus below the exit port of the concentrator,is designed by the method mentioned.The model of the concentrator is established by SolidWorks,and its optical performance is simulated and analyzed by the optical software.The optical performance analysis shows that the maximum acceptance half angle of the concentrator is up to 25 °,which is larger than that of the original concentrator.