Dynamic characteristics and performance analysis of typical liquid carbon dioxide energy storage systems

Liquid carbon dioxide energy storage holds significant promise for stabilizing renewable power due to its high efficiency and compactness. However, the dynamic thermodynamic behavior in storage tanks and its system-level impacts remain underexplored. This study employs unsteady-state modeling to elucidate the real-time effects of tank parameters on performance of three typical liquid carbon dioxide energy storage systems, supported by comprehensive performance comparison and parametric analysis. Results indicate that synchronous fluctuations of tank pressure and temperature during carbon dioxide inflow and outflow are main factors affecting the operation of system components. Constant-pressure operation outperforms sliding-pressure mode in operating persistence, with cryogenic high-pressure system showing a 3.47 % reduction in runtime under the latter. At design conditions, the gas-liquid conversion system achieves optimal round-trip efficiency of 60.23 % in constant-pressure mode, while the cryogenic high-pressure system attains the highest energy storage density of 4.843 kWh/m³. In contrast, the dual high-pressure system underperforms due to its minimal 3.14 % tank space utilization. To further boost system performance, attention can be paid to the design of turbomachinery and heat exchangers, and the improvement in tank utilization. Parametric analysis further reveals that appropriately lowering the volume and maximum pressure of low-pressure storage tanks while increasing counterparts of high-pressure storage tanks enhances system metrics. Compared to the natural convection storage tank model, both isothermal and steady-state models improve system performance, whereas the adiabatic model only benefits round-trip efficiency. The steady-state model maximizes tank spatial utilization, emerging as the most optimized model.