Evaluation of the performance and economy for a hybrid energy storage system using hydrogen and compressed carbon dioxide as the energy carrier.

• A novel green concept of hybrid energy storage system has been proposed. • Three system forms are presented to satisfy different needs in multiple scenarios. • The multi-objective optimization is carried out. • Potential solutions to improve the system economic performances are discussed. A green concept of hybrid energy storage system with hydrogen and compressed carbon dioxide as the energy carrier has been proposed in this paper. The integration of the two energy storage methods leads to a hybrid efficient storage way, which can have higher energy density and lower pressure tank volume compared to the compressed carbon dioxide, and has higher energy storage efficiency compared with the hydrogen one. The ratio of the two energy storage is determined by the hydrogen consumption way. In this paper, the hydrogen fueled gas turbine with carbon dioxide as the working fluid (Allam cycle) is used for large amounts of the hydrogen consumption, and the mass flow rate ratio of hydrogen and CO 2 is 0.0048 at the design point. The combined system can be used for inter-regional power dispatching, peak and frequency modulation and so on. A basic system form is firstly introduced, and the round trip efficiency (RTE) and levelized cost of electricity (LCOE) are 42.41% and 0.2075 $/kWh at the design point, respectively. In addition, two improved types are proposed. The effect of key parameters, including the CO 2 compressor outlet pressure, the CO 2 compressor inlet pressure and the CO 2 mass flow rate, on the system performance is performed. The multi-objective optimization is also conducted. The comparison reveals that the improved form-I performs with a lower LCOE and a weaker RTE. In contrast, the improved form-II owns a better RTE but a higher LCOE. It can be concluded that the improved form-I can improve the economic performance of the energy storage system through the optimization of the compressed carbon dioxide high pressure storage subsystem. And the improved form-II can enhance the thermodynamic performance by adding the transcritical carbon dioxide cycle branch. Potential solutions to improve the system economic performances are also discussed and the results indicate that technology development, subsidies and electricity market transaction premium would be beneficial for the large-scale promotion of the system in practical. [ABSTRACT FROM AUTHOR]