Operational dynamics and long-term stability in the novel CO-based electrothermal energy and geological storage system in salt cavities

Abstract

The massive integration of renewable energy sources and the development of advanced technologies to mitigate climate change are key factors in the energy transition towards a sustainable model. Increasing the contribution of renewables to the electricity market requires developing new energy storage systems. The novel CO 2-based electrothermal energy and geological storage system could be a viable option for large-scale storage in renewable power generation plants in the near future. This system utilises transcritical CO 2 cycles to convert electrical energy into thermal and mechanical energy, enabling integration with carbon capture and storage systems in geological formations, with an initial efficiency range of 52.8–61.5%. This dual approach enhances energy storage capabilities and contributes to reducing atmospheric CO 2 levels, offering a sustainable solution to address both energy and environmental challenges. This study evaluates, for the first time, the subsurface potential as a thermohydraulic buffer that ensures long-term operational stability and pressure management. Through long- term temporal simulations, a numerical model featuring coupled thermohydraulic simulations has been devel oped to incorporate subsurface heat transfer processes, considering a salt cavern scenario. Different scenarios are analysed depending on the characteristics of the production/injection processes, well depth, cavern size, or storage time. The research identifies a critical transition from an initial transient phase to a dynamic steady state. The results demonstrate that while operational fluid streams almost entirely govern the system’s short-term energetic response, geothermal interaction could be critical for long-term stabilisation. The energy gain dur ing injection directly influences the required CO 2 conditions at the wellhead. Wellhead pressure and temperature must be adjusted according to the desired conditions at the bottomhole. Maintaining high-pressure conditions in the salt cavern is essential to ensure proper coupling with the surface cycles and to operate with high electricity- to-electricity conversion efficiencies, reaching the range of 50.3–65.6% when the pressure approaches the upper limit. Active management of mass flow rates and pressures, along with advanced thermal control strategies, will be essential to improve system efficiency and flexibility.