Thermodynamic and economic assessment of compressed carbon dioxide energy storage systems using a post-mining underground infrastructure

The paper presents the results of thermodynamic and economic analysis of a compressed carbon dioxide energy storage system using low-pressure reservoir, where carbon dioxide cannot be stored at a high-pressure, like in standard concepts. Such limitations may occur in post-mining underground excavations, the availability of which will increase in the coming years due to the ongoing decarbonisation of economies in many countries. In this paper the concepts of two systems using an isobaric high-pressure tank and a non-isobaric low-pressure reservoir which are built within a post-mine shaft are presented. The paper presents the results of technical analysis for systems with various structures. The results of the analysis show the storage potential and effectiveness of the compressed carbon dioxide energy storage system, which includes one, two or three sections of carbon dioxide compressor together with thermal energy storage tanks and the same number of expander's sections. The analyses were carried out for various ranges of allowable pressure change in the low-pressure reservoir. The paper identifies the pros and cons of the systems, such as high values of energy storage efficiency (which may reach almost 80%) and their technical complexity. The storage capacity and the required tank volumes were also assessed. For the system with single-section compressor and single-section expander, more in-depth analyses were carried out. The analyses were carried out for the assumed geometry of the mine shaft. For this solution economic analysis were also carried out. For the decision variables considered, the Levelized Cost of Storage ranges from 314.6 to 439.4 euro/MWh. The inspiration for the development of the system was the high storage potential of underground mine infrastructure available in the region of the Upper Silesia located in Poland; however, the solution is universal and may be applied in other industrial regions.