Energy storage system based on transcritical CO2 cycles and geological storage

•Energy storage system based on transcritical CO2 cycles and renewables.•System combines reversible heat pump, CO2 capture and geological storage.•Electric to electric Round-trip efficiencies reach 42–56%.•Efficiency affected by location: depth of the well and availability of renewables.•Flexible system to operate under different scenarios for decarbonization. The use of CO2 as a working fluid in power generation and storage applications has experienced a significant boost in recent years, based on its high-performance characteristics in power generation or heat pumps. This work proposes a novel combined use of transcritical CO2 cycles as an energy storage system and carbon dioxide storage inside geological formations. In this work, the layouts for concept integration were developed. They were adapted to operate under different scenarios and operation modes based on storing energy from renewable sources or storing energy to capture CO2. The preliminary results show these cycles as promising energy storage technologies, with a high potential to compete in terms of electric to electric storage efficiencies (42–56%) and costs (70–120 USD/MWh). Besides, results show that more than 1 Mton/year of CO2 could be additionally stored with this renewable energy storage concept depending on the conditions. These results show the opportunity for the concept as an energy storage system, with special interest when combined with carbon-intensive industries as cement or chemicals.