| Improving the proportion of solar energy in China ' s energy structure and energy utilization efficiency is an important technical means to achieve the dual-carbon goal.Optical fiber transmission solar system provides a new technical route for the development of solar energy,which is a promising technical approach.Optical fiber is an efficient energy transfer medium,which can realize the long-distance transmission of light by using the low loss characteristics of optical fiber.The solar energy is coupled into the optical fiber to realize the free transmission of space light,and the sunlight can be introduced into the room where the sunlight cannot be directly irradiated.Solar energy transmission through optical fiber as a new solar energy utilization technology has been widely used in photovoltaic,photothermal,lighting and other fields.At present,solar fiber lighting has made preliminary progress,but the low coupling efficiency of optical fiber and the low transmission efficiency of wide spectrum restrict the development of solar fiber energy transmission technology.Using flat convex lens as secondary concentrating device can reduce the size of solar focusing spot.At the same time,the full spectrum of solar light is divided into narrow-band spectrum by using the splitter.In this study,a two-stage concentrating solar fiber coupling energy transfer system with Fresnel concentrator and flat convex lens is proposed.In this system,the selective input of solar spectrum by splitting can effectively improve the coupling efficiency and improve the energy transfer effect of the system.The main research contents of this paper include :(1)The energy loss characteristics of Fresnel concentrator are analyzed,and the focusing spot and spot energy distribution characteristics of Fresnel concentrator and two-stage concentrator system are analyzed.The influence of the three coupling losses of the fiber on the coupling efficiency is studied,and the coupling chromatic aberration loss model is established.The transmission loss affecting the fiber is analyzed.The results show that the spot size after two-stage concentrating decreases with the increase of wavelength.It can be seen from the chromatic aberration model that when the incident spectrum is determined,there is a minimum spot size with the moving of the fiber position.At this time,the coupling efficiency of the fiber is the largest,that is,the optimal coupling distance of different spectra is different.The larger the wavelength is,the larger the optimal coupling distance is.(2)Experiment and analysis of Fresnel concentrating system and fiber coupling energy transfer.The experimental platform of Fresnel concentrator was set up to measure the size,energy distribution and temperature distribution of the spot.The spot size of Fresnel lens spot at different locations was measured by experiments.the measured Fresnel concentrator concentration ratio is 900.The energy density distribution characteristics of the spot measured by the experiment are in accordance with the Gaussian distribution.The energy of the focusing center is the highest,and the energy decreases sharply from the center of the optical axis to the surrounding,which is consistent with the simulation results.(3)A laser fiber coupling energy transfer experiment platform was built to test the coupling transmission characteristics of fiber under different spectra and the influence of fiber core diameter on coupling efficiency.The experimental results show that the focal length of different spectra through the same coupling lens is different.The highest coupling transmission efficiency of 532 nm green laser is 82.16 %,and the coupling distance is 15 mm.The highest coupling transmission efficiency of 660 nm red laser is 80.556 %,and the coupling distance is 16 mm.The optimal coupling distance of long spectrum is greater than that of short spectrum.Moreover,the coupling transmission efficiency of the fiber can be effectively improved by increasing the diameter of the fiber core.When the fiber core increases from 0.5 mm to 1.5 mm,the coupling transmission efficiency of the fiber increases from 28.947 % to 82.164 %.(4)By establishing the model of Fresnel lens and optical fiber transmission system in Tracepro,the energy density distribution characteristics and spot size of Fresnel lens spot at different positions are obtained by simulation calculation.The simulation model is verified by comparing the experimental results with the simulation results.The results show that the energy distribution characteristics and spot size of the spot are consistent with the experimental results.(5)The coupling transmission characteristics of different spectra and the influence of oblique incidence of light on the coupling efficiency are simulated,and the relationship between the optimal fiber coupling distance and the spectrum is verified.The simulation results show that the coupling efficiency of the fiber decreases gradually with the increase of the deviation angle of the light relative to the optical axis.When the deviation angle is greater than 1 degree,the coupling efficiency is close to zero.Moreover,the chromatic aberration of broad-spectrum sunlight through the coupling lens will lead to different optimal coupling distances of different spectra : the optimal coupling distance of infrared spectrum is the largest,the optimal coupling distance of full spectrum is the second,and the optimal coupling distance of visible spectrum is the smallest.(6)The Fresnel concentrator,flat convex lens and optical fiber two-stage concentrator fiber coupling transmission system is established in Trace Pro.The influence of two-stage concentrator coupling on coupling efficiency and transmission efficiency is studied,and the results of direct coupling are compared.The simulation results show that the coupling efficiency of the two-stage concentrating system is higher than that of the direct coupling when the different spectra of sunlight are focused by Fresnel lens.The coupling efficiency of infrared spectrum by adding a flat convex lens coupling fiber is up to 57.4 % higher than that by Fresnel lens focusing directly coupling fiber.The coupling transmission efficiency of different spectra is different.The visible spectrum is the largest,followed by the full spectrum,and the infrared spectrum is the smallest.When the direct coupling method is adopted,the coupling transmission efficiencies of visible light spectrum,infrared light spectrum and full spectrum are18.839 %,14.909 % and 16.358 %,respectively.When the two-stage concentrating fiber coupling method is adopted,the coupling transmission efficiencies of visible light spectrum,infrared light spectrum and full spectrum are 52.627 %,43.480 % and47.581 %,respectively.The coupling transmission efficiency of visible light spectrum is improved by 33.788 % when the two-stage concentrating fiber coupling method is adopted. |
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