Study On Cascade Solar Photovoltaic-thermoelectric Hybrid Generator System

The solar energy is expected to be the ultimate energy of human by the merits of non-pollution, wide distribution, extreme abundance, free of charge, etc. Photovoltaic cell, whichis one of the main ways of solar utilization, can convert solar energy to electricity directly.However, photovoltaic cell can only convert small part of solar energy to electricity becauseof low efficiency, a majority of solar energy is converted into waste heat, enhancing theefficiency of photovoltaic electricity generation is the main research direction in the field ofsolar power. Thermoelectric(TE) generation is one technologywhich can convert heat directlyinto electricity by Seebeck effect, with the advantages of without vibration, without noice,without wear, small size, light weight, high reliability, long life, non-pollution, etc. Byattaching TE modules to the back of PV panel, we can get a cascade PV-TE hybrid generatorsystem. In this system, TE modules convert the waste heat produced during PV cell works toelectricity, giving rise to the solar conversion efficiency.Firstly, the present thesis carried out the multiphysics numerical simulation andexperimentalresearch ofTE module. The multiphysics model ofTE module is developed, andthe effectsofthetemperature difference acrosstheTE module, theoutput current ontheoutputpower and efficiency of TE module are investigated. The model is validated throughcomparing the results of simulation and experiment. Results show that, the efficiency andpower of TE module both increase with an increase in temperature difference across themodule. The efficiency and power approximately follow linear and parabolic relations withthe temperature difference, respectively. In addition, the output current of TE module has agreat influence on the efficiency, power and the heat absorbed by the hot side of TE module.Enhancing the temperature difference across TE module is crucial for TE generation. Theseconclusionsobtained canprovide important guidanceforthedesignofPV-TEhybrid generatorsystem.Secondly, a comprehensive model for PV-TE hybrid generator system is established andsimulated. A novel PV-TE (denoted by PV1-TE) hybrid generator system, in which theceramic substrate of TE module is also used as the back panel of PV panel, is proposedaccording to the simulation result. The effects of many factors on the performance of PV1-TEis computed and discussed, such as solar irradiance, air temperature, wind speed, the output current of TE module, the length of TE element, etc. Compared to traditional PV-TE hybridsystem, the temperature of PV in the proposed PV1-TE hybrid system decreases and thepowers of both PV and TE increase significantly. The power of PV1-TE increases rapidly asthe solar irradiance increases. As the air temperature increases, the power of PV in the PV1-TE hybrid decreases, but the power ofTE module almost remains the same. As the wind speedincreases, the power of PV in PV1-TE hybrid generator system increases, however, the powerof TE module decreases simultaneously. The output current of TE module not only influencesthe power of itself, but also has an effect on the power of PV to some extent. As the coolingability of the cold side ofTE module increases, the powersof traditional PV generator system,PV1-TE hybrid generator system, PV1and TE module all increase. But the growth ratedecreases gradually and tends to zero finally. As the length of TE leg increases, the power ofPV decreases, but the power of TE module increases. The power of PV1-TE hybrid systemwith high performance TE material is higher30%than that of traditional PV system when thetemperature difference of TE module reaches10K.Finally, PV1-TE hybrid generator system is investigated experimentally. Prototypes oftraditional PV and PV1-TE are prepared and their output properties are researchedcomparatively. The effects of solar irradiance and cooling ability on the performance of PV1-TE hybrid generator system are discussed. The experimental results and parts of simulatedresults are compared simply. The power of PV1-TE hybrid generator is5.37percent higherthan that of traditional PV when the solar irradiance is160mW/cm2and the temperature ofcooling water is5℃.In conclusion, the present paper systematically research a cascade PV-TE hybridgenerator system. The obtained conclusions provide important guidance for the design andoptimization of PV-TE hybrid generator system.