Mechanism And Experiment Investigation On Solar Thermophotovoltaic System

With the increasing shortage of the energy, many countries are committed to seeking a new kind of electricity generation plant. As clean energy, solar energy has incomparable superiority since it is not only primary energy, but also renewable energy. Solar thermophotovoltaic (STPV) is another way of solar energy utilization. Modularity, portability, absence of moving parts, pollution-free, high efficiency, high power density are key advantages of STPV systems, which may have a wide application prospect. The purpose of this thesis is to investigate the operational mechanisms of STPV system, optimize the various component parts and carry out a comprehensive experimental study. The detailed contents are focused on the following aspects: (1) Numerical investigation of the mechanism of the solar thermophotovoltaicAn integrated theoretical analysis model of the STPV system is constructed. Monte-carlo method is used to investigate the convergence characteristic of the dish reflector, the effects of the non-parallelism of sun rays, tracking errors and reflection errors on the size and location of the facula are numerically analyzed. The physical model of the heat transfer and thermo-electricity conversion process in the TPV system is constructed, the effects of the characteristic parameters on the cell performance are discussed; also, a model of predicting the performance of the whole STPV system is presented and the relation of the concentration ratio, the emitter temperature, cell temperature and the velocity in the cooling system is investigated in depth, which provides necessary theoretical guidance for the optimization design of the STPV system.(2) Design of the STPV systemThe main component parts of the STPV system including the emitter, the filter and the cooling system are designed in this thesis. A numerical model of predicting the performance of the emitters with different configurations and materials is presented. The cut-off factor and the energy loss of the different emitters are analyzed, also the temperature distribution and its impact on the system performance are simulated. Simultaneously, the energy utilization and the system efficiency of the different selective emitters and the graybody emitter with photonic crystal filter are compared. The one-dimensional micro-structure spectral control device are numerically designed for the GaSb cell, also the matched characteristics with the cell and the power distribution of the emitter are analyzed. A new type of water cooler for STPV systems is designed and the numerical simulation of heat-transfer and flow performance is operated in virtue of CFD software. The influence of the configuration, the material and the velocity on the cooling performance is investigated.(3) Thermal analysis of the STPV systemAn in-depth research on the heat exchange process in the STPV system is done. A 3-D model is used to investigate the approximate estimation of the natural convection heat transfer in the emitter cavity, and the effects of the free convection heat loss on the emitter temperature and the output characteristics of the cells are discussed. Also, some improvement methods are proposed to reduce the free convection loss without affecting the amount of the solar energy absorbed. The performance of the improved system is compared with the system with open emitter and provides a theoretical guidance for the system optimization. The energy exchange between the emitter and the cell in the TPV converter is studied and the physical model of the heat transfer of free convection and radiation is constructed. The influence of the emitter temperature on the radiation and convection heat load in the cell is analyzed, also the effects of the free convection heat transfer on the system performance are discussed. Meanwhile, the cell output power and system efficiency under different emitter temperature, inlet velocity of the cooling system and the cell heat load with the existence of the free convection are studied. The optimal inlet velocity corresponding to every emitter temperature is obtained by the optimization algorithm in order to get the optimum working conditions.(4) Optimization of the STPV system and the investigation with the second law of thermodynamicsAn optimal design method of the STPV system is established to further improve the system performance and the conversion efficiency. Aimed at the energy leakage at the entrance of the radiator, a selective film with the optimized cut-off wavelength is put forward as it will reduce the radiation loss. Based on the second law of thermodynamics, a theoretical model is established for efficiency analysis and optimization of the STPV system. The entropy production for the component modules involved in the whole system assembly is analyzed. The effects of the concentration ratio, emitter temperature, energy bandgap, cell temperature on the entropy and the efficiency are investigated and an in-depth discussion of the STPV system is carried out from another point of view.(5) Experimental study of the STPV systemThe whole STPV system is experimentally investigated in this thesis. The subassemblies of the system including the concentrator, the emitter, the filter, cells and the cooling system are selected and processed, also the performance of the concentrator, the cooling system and the PV cells are tested. The TPV converter is designed and put up, combined with the auto-tracking module, the whole system is tested. The influence of the solar radiation on the emitter temperature is analyzed and the temperature distributions of the emitter under different inlet conditions are compared. The ouput characteristics of the cells under different emitter temperatures are measured and the effects of the velocity in the cooling system on the cell temperature and output power are investigated. Finally, the reasons for the difference between the theoretical and the experimental results are discussed.