Proposal and assessment of a novel carbon dioxide energy storage system with electrical thermal storage and ejector condensing cycle: Energy and exergy analysis

The intermittent nature of renewable energy leads to significant issues when increasing the penetration level of renewable power. Energy storage system is generally considered to be an efficient measure for stabilizing the fluctuations of renewable power. A creative liquid carbon dioxide energy storage system integrating with transcritical Brayton cycle, electrical thermal energy storage and ejector condensing cycle is kindly proposed in this paper. To evaluate the feasibility of the developed system, the system thermodynamic model is clearly established and verified. The parametric analysis is performed based on energy and exergy methods to assess the relationships between key functioning variables and the system performance. The analysis results indicate that the ejector condensing cycle can be introduced as a green solution to the dilemma of carbon dioxide condensation during discharging stage. A higher turbine inlet pressure and temperature both bring about a promotion of the system net power output as well as the round trip efficiency. The ejector entrainment ratio gives a decrease with the rise in ejector back pressure, and the decreasing trend is first steep until the ejector back pressure being at 8.2 MPa in the considered conditions and then becomes distinctly moderate. Meanwhile, the optimal system efficiency is always located at the constant ejector back pressure (8.9 MPa in the considered conditions). The exergy destruction within the ejector condensing cycle decreases substantially with the low pressure storage temperature, increases monotonically with turbine inlet pressure, keeps unchanged with turbine inlet temperature and decreases with ejector back pressure.