Experimental study of a compressed carbon dioxide energy storage system under different phases: Focus on reservoirs’ dynamic behaviour

• Provide innovative experimental data of filling/emptying CO 2 tanks. • Comprehensive analysis of the dynamic behaviour of the CO 2 tanks. • Better understanding of CCES operating process with liquid storages. Energy storage systems are becoming a highly topical issue with the increasing integration of solar and wind energy into the electricity mix. Thermomechanical energy storage systems are attracting growing interest. They are based on thermodynamic cycles to store electricity under mechanical and/or heat energy. Compressed CO 2 energy storage systems are one emerging example. Despite numerous modelling studies, experimental investigations remain very limited. Existing experiments are restricted to gaseous CO 2 at low pressures. However, these systems are mostly investigated with storage tanks containing liquid or supercritical CO 2 . This study addresses this gap by presenting the first experimental results on the dynamic behaviour of reservoirs containing CO 2 in multiphase conditions (coexistence of liquid – gaseous CO 2 ) and reaching supercritical pressures. For that purpose, an experimental test rig based on conventional and commercial components was developed. It is composed of a 320 L low-pressure storage, a 240 L high-pressure storage and a 3 kW CO 2 pump. The mass flow rate ranges from 100 to 320 kg.h −1 , corresponding to charging times from 1 to 1.8 h (including a balancing step) with a maximal pressure of 22 MPa. The results indicate an inability to maintain a constant pressure during a tank emptying or filling due to temperature changes. During a discharge, the pressure in the high-pressure storage drops from 22 to around 3 MPa. As a consequence, this study highlights the possibility to balance the pressure after a discharge.