Thermodynamic analysis of a novel liquid carbon dioxide energy storage system and comparison to a liquid air energy storage system

Renewable energy is difficult to utilize efficiently due to its intermittent. Energy storage system is commonly considered to be an effective solution to stabilize fluctuations of renewable energy. In this paper, a novel liquid carbon dioxide energy storage system (LCES) with two artificial storage tanks based on Rankine cycle is proposed. A comparative study is carried out between the LCES and the liquid air energy storage system (LAES) to evaluate their performance. Thermodynamic models are established, then energy and exergy analyses are carried out for both systems. The effects of key parameters on both system performance are compared. Finally, the influence of the solar energy as a heat source on the performance of LCES is analyzed. The results show that LCES has a relatively high round trip efficiency (RTE) and exergy efficiency compared to LAES, but a lower energy generated per unit volume (EVR). The RTE, exergy efficiency and EVR of the LCES system under design conditions are 45.35%, 67.2% and 18.06 kWh/m³, while those of the LAES are 37.83%, 45.48%, and 101.6 kWh/m³, respectively. However, for LAES system, the total volume of liquid tanks is 2493 m³, which is close to the total volume of LCES (2383 m³), because it need extra four tanks for cold medium storage. The solar fluctuations have little effect on the turbine inlet temperature of the LCES.