Energy Management Technologies And Efficient Improvement Metohds Of High-temperature Cell System

Energy storage systems based on electrochemical cells are attracting huge attentions because they have the advantages of large scale, low cost and flexible distribution. Enery management as one of the key methods to enhance energy efficiency in electrochemical cell system is becoming more and more important. Heat generation is normally the big waste in electrochemical energy storage system, which means the heat management is one of the main approaches of the energy management.For low temperature system, the cogeneration/utilization of heat and electricity is the main choice for energy management. However, a big challenge is the heat management for high temperature electrochemical cell system. More importantly, the enengy efficiency is required to be high than 80% for commercial utilization,especially for the commercial high temperature electrochemical cell system. However,traditional heat storage/utilization method is not sufficient to enhance the roundtrip efficiency to as high as 80%. Therefore, it is necessary to develop a novel and effective method for heat storage in high temperature electrochemical cell system. In this thesis,we take the high temperature solid oxide cell system as an example,combing the phase-change metal for high temperature heat storage/utilization with a solid oxide cell system. We investigate the electricity storage and utilization,electricity roundtrip efficiency and its influcnece factors,and then we discuss and provide effective approaches for energy management improvement.Firstly, it is a big challenge to store and utilize the high temperature heat in the high temperature energy conversion cells and the huge heat loss is one of key problems in high temperature heat management. In this chapter, we consider the specific requirement for high temperature heat management and then we construct a model based on phase-change metal for heat storage/utilization. We then combine the heat management system with a typical high temperature electrochemical cell system like solid oxide cell system, to construct a combined system for heat management in high temperature electrochemical cell system, which is the basis for the following work in this thesis.Secondly, we study the electricity storage/generation in a reversible solid oxide cell stack with silver tank for energy storage. The model is set up and utilized for the calculation. The system heat is for the first time tentatively stored in a silver metal with phase change when the stack is operated to generate electricity in fuel cell mode and then reused to store electricity in an electrolysis mode. The state of charge, H2 frication in cathode, effectively enhances the stack OCVs while the gas pressure in electrodes also increases the OCVs. On the other hand, higher system pressure facilitates the species diffusion in electrodes that therefore accordingly improve electrode polarizations. With the aid of recycled system heat, the roundtrip efficiency reaches as high as 92% for the electricity storage and generation.Thirdly, we investigate the heat storage and utilization based on copper metal tank to enhance the electricity cycling efficiency in the solid oxide cell system. The model is set up and utilized for the calculation. It is found that the OCVs of this planar solid oxide cell system rely on more on the state of chare than system pressure and the cell polarization resistances mostly come from the fuel electrode polarization. The system temperature can be effectively changed by the heat balance of gas, cell component and operation circumstance. While the heat loss in the system has a huge influence on the system temperature and electricity cycling efficiency. It is found that the electricity cycling efficiency can be reaching 80% when copper tank is utilized for heat storage in fuel cell mode and heat utilization in electrolysis cell mode.Fourthly, we consider the effective approaches for enhancing electricity cycling efficiency by analyzing the heat storage and utilization in the solid oxide cell system.It is found that the energy storage capacity can be effectively increased at high operation pressure or by enlarging the heat storage capacity. The state of charge,system operation temperature and amount of phase change metal only change the energy storage capacity but contributes less on the electricity cycling efficiency.However, the operation conditions like high current are favorable for the enhancement of electricity cycling efficiency.Finally, we report the modifications of the model of the solid oxide cell system. We firstly analyze the reported work and then conducted the experimental work to confirm the Faraday current efficiency of solid oxide cell in fuel cell and electrolysis cell mode. Then we use the data to calibrate the balance of state of charge in the system in fuel cell and electrolysis mode, which accordingly influences the electrochemical heat generation/absorption and even the operation time.