Integration of energy storage systems based on transcritical CO2: Concept of CO2 based electrothermal energy and geological storage

Abstract

Energy storage systems are crucial for the massive deployment of renewable energy at a large scale. This paper presents a conceptual large-scale thermoelectrical energy storage system based on a transcritical CO2 cycle. The concept is developed through the analysis of three high-efficiency systems: renewable energy storage using a thermoelectric energy storage system based on a reversible heat pump; a CO2 storage system; and novel integration of energy storage using a reversible heat pump and geological injection of CO2. The latter system efficiently integrates energy and CO2 storage, taking advantage of the synergies between the operational requirements of both systems. The system uses CO2 captured in stationary sources as a working fluid to store energy from renewables. The energy is stored and recovered in geological formation and heat/cold tanks, with energy storage based on sensible or latent heat of ice and water. A fraction of the CO2 is expected to be permanently sequestered in the geological formation. The analysis of the time evolution of the system, under different operation profiles, shows the interest of the concept as a feasible integration for energy storage and CO2 capture based on renewable energy, with an electric-to-electric efficiency varying between 40 and 50 %.