| With the increasing penetration of renewable energy into the power grid,the uncertainty and intermittency of renewable energy sources have brought significant challenges to the operation of the power grid.Energy storage systems are considered an effective way to solve these challenges.The excellent thermal properties of carbon dioxide make compressed carbon dioxide energy storage system more technological and economical.However,in current researches,the steady-state characteristics analysis of compressed carbon dioxide energy storage systems has been mostly focused,while parameters such as the pressure of the storage tank and the efficiency of the compressor and expander will result in the variable system operations,resulting in system performance deviating from its designed conditions.However,researches on the dynamic characteristics of compressed carbon dioxide energy storage systems are still incomplete and need further improvement.Therefore,in this paper,the steady-state and dynamic characteristics of compressed carbon dioxide energy storage systems are investigated and compared.The main research contents are as follows:Firstly,in this research,the steady-state characteristics of the compressed carbon dioxide energy storage system are studied and the models for subcritical,supercritical,and liquid compressed carbon dioxide energy storage systems are established.The effects of changes in thermodynamic parameters on the compressed carbon dioxide energy storage system are studied by genetic algorithms to explore the upper limit of the round trip efficiency of the compressed carbon dioxide energy storage system.The results show that the round trip efficiency of the subcritical,supercritical,and liquid compressed carbon dioxide energy storage systems would be 66.9%,71.6%,and 70.0%,respectively.Secondly,to investigate the dynamic characteristics of compressed carbon dioxide energy storage systems,dynamic models of compressed carbon dioxide energy storage system are established and an experimental bench of compressed carbon dioxide energy storage system was built to verify the dynamic system models.The performances of the compressed carbon dioxide energy storage system under four working modes are analyzed and the maximum capacity of the compressed carbon dioxide energy storage system is explored.The results show that the round trip efficiency of the compressed carbon dioxide energy storage system under the off-designed power operation mode and designed constant power operation mode were 4.92%and 3.16%,respectively.Through the exploration of the maximum capacity of the compressed carbon dioxide energy storage system,it is found that the capacity of the compressed carbon dioxide energy storage system increased at first and then decreased with the increasing load,and there is a maximum value.Finally,in this research,the steady-state and dynamic characteristics of compressed carbon dioxide energy storage systems are compared.The cost models for each component of compressed carbon dioxide energy storage are established to compare the thermodynamic and techno-economic characteristics of steady-state and dynamic systems.It is found that under steady-state operation,both the charging time and discharging time of the compressed carbon dioxide energy storage system are longer than the duration of dynamic operation.However,the exergy efficiency of the compressed carbon dioxide energy storage system is lower under steady-state operation,which is 20.39%,and the exergy efficiency under dynamic operation is 48.77%. |
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