4E (Energy, Exergy, Economic, Environment) analysis and optimization of a multigeneration system integrating two energy storage systems for remote islands

• A multigeneration system is presented based on two energy storage systems . • Combines renewable energy, CO 2 energy storage, Carnot battery and reverse osmosis . • Considers non-adiabatic pipeline model for underwater CO 2 transport. • Energy, exergy, economic, and environmental analyses and system optimization. • Optimized round trip efficiency of system is 63.38%. Remote island areas, due to their unique geographical locations, possess abundant renewable energy resources. However, fluctuations in these resources make it essential to integrate energy storage systems to enhance energy reliability and improve the energy consumption situation for residents. Therefore, this paper presents a multigeneration system based on underwater compressed CO 2 energy storage and the Carnot battery, which supplies electricity, thermal energy, and freshwater. The system includes an underwater CO 2 storage subsystem, a Carnot battery subsystem, and a reverse osmosis desalination subsystem. Performance is evaluated across energy, exergy, economic, and environmental aspects, with key factors such as heat storage temperature, underwater pipeline diameter, compressor pressure ratio, and CO 2 mass flow rate analyzed. Results show that increasing thermal storage temperature and pipeline diameter improves overall system efficiency, and round trip efficiency rises from 52.70% to 67.54% as temperature increases from 95 ℃ to 135 ℃. However, a higher compressor pressure ratio and CO 2 mass flow rate reduce performance. Under optimal conditions, the system achieves a round-trip efficiency of 66.46% and a levelized cost of electricity of 0.4134 $/kWh. A multi-objective optimization shows that a round-trip efficiency of 63.38% and a reduced electricity cost of 0.3874 $/kWh are achievable.