Avoidable exergy performance analysis in the integration of an electrothermal energy system based on transcritical CO2 cycles

• Exergy approach based on the effects of integration between the components of a system. • Analysis based on avoidable exergy destruction in storage systems. • Study based on the optimal points of a storage system and its key parameters. • Exergy analysis of a novel CO 2 electrothermal energy and a geological storage system. This paper develops an exergy approach to analyse avoidable exergy destruction in complex systems, which can lead to significant results when applied to storage systems. The proposed methodology in this paper has been applied to a novel CO 2 electrothermal energy and geological storage system. The methodology follows a two-step approach. In the first stage, an analysis of the different components individually, considering their operational characteristics, identifies their thermodynamic limits and the related unavoidable exergy destruction in each component. In a second stage, the exergy study at the system level, which comprises off-design models, integrates the components and provides valuable insights into the system’s dynamic behaviour based on the interaction between components. The avoidable exergy performance is defined as the comparison between the avoidable exergy destruction of the system and the unavoidable exergy of the components, which can be used as an indicator of the integration impact. For the case of the novel energy storage concept, the individual study of the components has shown that the unavoidable exergy destruction takes a value of 22.69 kJ/kg CO2, and the compressor is the most critical component. The dynamic behaviour of the system based on integration has shown that the avoidable exergy destruction, under these conditions, is 32.77 kJ/kg CO2 when the load rate takes an optimal value, achieving an avoidable exergy performance of 75.3 %. These results lead that under optimal conditions, the system cannot achieve the unavoidable exergy destruction, which is based on opposing behaviours between the components. The sensitivity analysis based on design parameters leads to an improved avoidable exergy performance of up to 18.2 %.