| Solar energy is clean,widely distributed and free of charge.It is one of the most promising energy sources.Fuel cell is based on the galvanic cell reaction.So the energy conversion efficiency is not limited by the "Kano cycle",the theoretical efficiency can reach up to 90%.The Combined Cooling,Heating and Power(CCHP,Trigeneration)system can realize the energy cascade utilization to improve energy utilization rate.Therefore,the trigeneration system based on solar energy and fuel cells is an energy system with low cost,low cmission and high efficiency.The research on this kind of energy system can effectively improve the energy efficiency,ease the energy shortage,and improve the single energy structure situation in China.The main research content of this work is the efficient utilization of solar energy and fuel cell,and the key issue is the energy conversion.A type of solar thermal conversion system based on new structure is presented with its physical model in this work.The geometrical optics model of the concentrating system based on Monte Carlo ray tracing principle is developed to study the optical properties of the concentrator by means of numerical simulation,including the concentration ratio and the light loss in the cavity solar receiver.The thermodynamic model coupled convective and radiative heat transfer is established to analysis the effects of various factors on convection and radiation heat loss.A three-dimensional model for Proton Exchange Membrance Fuel Cell(PEMFC)is established based on the analysis of fuel cell energy conversion process.The aging characteristic of the sealing material for PEMFC is also experimentally studied.On this basis,a residential trigeneration system based on solar energy and PEMFC is proposed.The thermodynamic model of each subsystem and the energy consumption model,economic and environmental performance analysis model for the whole system are also developed.The cycle characteristics of the working fluids in the organic Rankine cycle are comparatively analyzed.Then,the energy efficiency,exergy efficiency,economic and environmental performance of the trigeneration system are theoretically analyzed.In the end,a multi hierarchy comprehensive evaluation model based on mixed grey theory is established to evaluat the synthetic performance.Through the above-mentioned research contents,the main conclusions are as follows:(1)The total error of concentrating system has a significant effect on the concentration ratio and the focal spot area,especially with small total error.There are some similarities in the optical properties of the cavity receiver with similar geometry.Compared with three traditional cavity solar receivers,the thermal performance of the improved one presented in this work is much better,and the total heat loss can be reduced by 6.5%?56.8%.(2)The fuel cells will produduce more water with large current density,which may easily lead to the decrease of the reaction gas partial pressure and affect the electrochemical reactions.The anode gas humidification is beneficial to the wettability of the proton exchange membrane,but the voltage will be reduced.The fuel cells can reach higher performance with higher operating pressure.The existence of water molecules can accelerate the aging of silicone rubber,especially at high temperature.(3)R601 is chosen as the best working fluid in the trigeneration system.The energy efficiency of system I in summer and in winter are 0.929 and 1.232,respectively.Moreover,the exergy can reach 58.3%.While the energy efficiency for system II are 1.190 and 1.391 in summer and in winter,respectively.The exergy efficiency is about 47.5%.(4)The primary energy saving rate in summer and in winter are 64.9%and 60.0%for system 1,and 31.8%and 36.2%for system II.The reduction rate of greenhouse gases,CO and NOx are 84.9%,97.9%and 90.8%for system ?,and 69.2%95.8%and 81.5%forsystem II.The payback period for the two systems is 9.56yr and 6.03yr.The trigerneration systems presented in this work show better performance compared with three other systems.System I can be used for long-term operation while the system ? is better in the short run.The solar thermal conversion model proposed in this work is consummate and applicable,which can provide a theoretical basis for the design and optimization of the subsequent collectors.The heat loss of the modified cavity solar receiver can reduce 6.5%?56.8%with good economic benefit.The proposed trigeneration system provides a more efficient utilization method for fuel cell and energy solar.The synthetic evaluation model can provide theoretical basis for the design and optimization of trigeneration system. |
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