Techno-economic analysis of a combined heat pump and liquid CO₂ energy storage system: A pathway for energy density enhancement

As the integration of intermittent renewable energy increases, efficient and reliable energy storage solutions are crucial for sustainable energy systems. Liquid carbon dioxide energy storage (LCES) has gained attention for its high roundtrip efficiency and lack of geographical constraints. This paper presents a novel hybrid system combining a heat pump cycle with LCES for 10 MW output. Excess electrical energy is stored as compression energy and high-temperature thermal energy. Waste heat from compression is recovered and stored as thermal oil through the heat pump cycle. During the discharging process, the turbine's output is enhanced by combining compressed and thermal energy, increasing the system's energy density. Thermodynamic and economic models are established to assess the hybrid system's performance, with exploring the sensitivity analysis of key parameters on system performances. Multi-objective optimization yields optimal exergy efficiency of 55.72 %, energy density of 32.11 kWh/m³, and a levelized cost of electricity of 0.1177 $/kWh.