Optimization Of The Photovoltaic-thermoelectric Hybrid System With And Without Optical Concentrator

Photovoltaic power generation can directly convert solar energy into electrical energy,which is an important means of utilizing solar energy.However,the current efficiency of photovoltaic cells is low,only a small part of solar energy can be converted into electrical energy,and the rest of the solar energy is reflected by photovoltaic cells or converted into waste heat.The efficiency improvement of solar power generation is the most important research direction in the field of solar power generation.The photovoltaic-thermoelectric coupled system has drawn widespread attention in recent years due to its potential utilization of full-spectrum solar energy.The output power of thermoelectric?TE?is usually much less than that of photovoltaic?PV?,because the temperature difference of TE module is usually very small.Thus,the optical concentrating method has been used to increase the temperature difference,but it increases complexity of the structure and extra cost for the sunlight tracking system.Another practical way is using the thermal concentrating method to increase the heat flux of the TE module.However,for there two PV-TE coupled systems i.e.optical and thermal concentrating systems,there exists a confrontation between the PV cell and the TE module.The efficiency of PV cell decreases with the increasing temperature,while the performance of the TE module increases with the increasing temperature difference.In some conditions,the total efficiency of the PV-TE coupled system may be even lower than that without TE module.Therefore,it is necessary to investigate the optimal combination mode of PV cell and TE module for the coupled system.In this paper,a thermodynamic model based on energy-balanced equation is established to investigate the structural optimization and efficiency improvement of PV-TE coupled power generation system,which considers the effects of the thermal concentration factor,the length of thermocouples,the ratio of load resistance to internal resistance of TE module,solar irradiance and thermal diffusion factor?the number of pairs of thermocouples,cross-sectional area of thermocouples?,optical concentrating ratio,cooling water flow rate.The influence rules of these factors on power generation efficiency of PV-TE coupled system without and with concentrator are also theoretically analyzed.The results of research are as follows:For the PV-TE coupled system without concentrator,the thermal concentration factor and the length of thermocouples have similar effects on the total efficiency of the coupled system.When the efficiency temperature coefficient of PV cells?_ref is small and the figure of merit of TE module Z is large,the optimal thermal concentration factor or the length of thermocouples exist to maximize the total efficiency of the coupled system.As the ratio of load resistance to internal resistance increases,the total efficiency of the PV-TE coupled system always increases first and then decreases.When?_ref is 0.001 K^-1,the total efficiency of the coupled system increases with the increase of solar irradiance.While?_ref ranges from 0.002K^-1 to 0.004K^-1,the total efficiency of the coupled system decreases with the increase of solar irradiance.For the PV-TE coupled system with concentrator,if the values of the thermal diffusion factor caused by individual changes in the cross-sectional area of the thermocouples or the number of pairs of thermocouples are the same,the influences of these two factors on the total efficiency of the coupled system are exactly the same.It is suggested that the thermal diffusion factor is about 3.0,and a larger total efficiency of the coupled system can be achieved with a smaller material cost.While?_ref is 0.001 K^-1,the total efficiency of the coupled system increases with the optical concentrating ratio increasing.In other cases,the total efficiency of the coupled system decreases with the increase of the optical concentrating ratio.When the cooling water flow rate is between 0.25m/s and 0.35m/s,the PV-TE coupled system with concentrator will have a higher overall efficiency.