Performance Analysis And Energy Matching Mechanism Of The Photovoltaic-Thermoelectric Hybrid System

With the aggravation of energy crisis,the exploration of the solar power generation becomes one of the most urgent demands.The photovoltaic cell(PV)is a dominant method to utilize the solar energy.However,the photons with long wavelength cannot be utilized by the photovoltaic cell;furthermore,the thermalization process makes the conversion efficiency of the photons with short wavelength low.The thermoelectric generator(TE)does not have requirement on the wavelength of the photon,it means that the thermoelectric generator can compensate the weakness of the photovoltaic cell,therefore more and more researchers pay their attention to the photovoltaic-thermoelectric(PV-TE)hybrid system.The key technical problem of the PV-TE is that the requirement of the PV temperature is different from that of the TE temperature.The larger temperature difference can improve the efficiency of the TE;however,it may be detrimental to the PV.Therefore,it needs to research mechanisms of the energy matching and energy transferring.This dissertation will give its attention to utilizing solar energy in full spectra and establish the design criteria of the PV-TE hybrid system.The main contents are as follows:(1)Research on the energy matching mechanism of the PV-TE hybrid systemThe influences of the crystalline silicon photovoltaic cell,silicon thin-film photovoltaic cell,polymer photovoltaic cell and copper indium gallium selenide photovoltaic cell(CIGS)on the PV-TE are studied.With the increasing of temperature,the efficiency of polymer PV cell first increases and then decreases,which is suitable for PV-TE hybrid system.The numerical results also show that,decreasing the thermal contact resistance,enhancing the convection heat transfer and raising the optical concentration ratio can increase the energy that can be utilized by the TE.(2)Research on the heat transfer mechanism of the PV-TE hybrid systemThe heat transfer process of the PV-TE hybrid system is investigated.The heat flux of the concentrating PV-TE hybrid system is high;therefore heat loss caused by the radiation and natural convection can be ignored in this system.The design of the concentrating PV-TE hybrid system needs to pay its attention to the thermal resistances of both sides of the TE.Sandwiching a copper plate between the PV and the TE can improve the efficiency of the concentrating PV-TE hybrid system by improving the temperature uniformity.It is suggested to use the water cooling system to enhance the heat transfer at the cold side of the TE.(3)Performance improvement of a photovoltaic-thermoelectric hybrid system subjecting to fluctuant solar radiationThe adjustable cooling blocks are introduced in the PV-TE hybrid system to reduce the temperature fluctuation caused by the variation of the solar radiation.The tested results and the theoretical analyses show that this design can make the PV-TE hybrid system operate around the optimum temperature throughout the day,therefore the efficiency of the PV-TE hybrid system can also be improved.(4)Integrated design of the PV-TE hybrid systemThe integrated design is used to simplify the structure of the PV-TE hybrid system and enhance the heat transfer.The ceramic plate and the heat conducting plate are removed from the PV-TE hybrid system to reduce the thermal resistance.A V type groove is designed to enhance the absorption of the solar energy.The tested results show that 20% improvement in the efficiency can be obtained by these methods.(5)Circuit matching of the PV-TE hybrid systemThe influence of the electrical design on the performance of the PV-TE hybrid system is studied.In the PV-TE hybrid system whose thermal resistance can be adjusted and the PV-TE hybrid system with the phase change material,the influence of the variation in the solar radiation on the PV temperature is low.Therefore,the electrodes of the TE and that of the PV should be connected in parallel in these systems.(6)The perovskite solar cell-TE systemThe feasibility and features of the perovskite solar cell-TE system is estimated.The constitutive relation between the optical characteristics and the performance of the perovskite solar cell-TE system has been researched.The potential methods to decrease the cost of the perovskite solar cell-TE system are studied.It is found that the temperature coefficient of the perovskite solar cell is low,therefore the efficiency of the perovskite solar cell-TE system is higher than that of the single perovskite solar cell.The features of the perovskite solar cell make the perovskite solar cell-TE system suitable for the condition without an optical concentrated system.The thermal concentration is proved a good method of decreasing the efficiency of the perovskite solar cell-TE system.In addition,the design of the perovskite solar cell-TE system needs to pay attention to decreasing the long-wavelength emissivity.