Analytical investigation of the compressor layout for off-design operation of a transcritical CO2 cycle in an electrothermal energy storage

Storage technologies are critical for the massive integration of renewable sources. Among the most promising storage technologies are those based on Carnot batteries. This work analyses CO₂-based electrothermal energy storage coupled with geological storage (CEEGS) under off-design conditions when integrated into a fluctuating system such as a PV system. The integration of simulation models over an annual cycle provides valuable insights into the dynamic behavior of the system, supporting informed decision-making for future research on such innovative technologies. The developed model enables the optimisation of both design and operational parameters, tailored to specific applications and geographic locations. The valuable information obtained has shown a bottleneck in the compressor that leads to a strong effect on the overall performance of the storage system based on technological limits and stored energy losses. In this regard, this work proposes different pathways based on compressor layout that can improve the integration of storage systems in general and, in particular, the system under study when integrated into fluctuating systems. The multi-compressor operating mode leads to an improved efficiency of up to 18% and an average increase in daily operating range of 1.5 h based on improved compressor adjustment. The proposed split flow for identical compressor operating mode shows a daily operating range equal to the multi-compressor operating mode and a slight loss of efficiency with respect to the multi-compressor operating mode because the first adjusts better with constraining system fluctuations. However, the latter is a simpler configuration, and it is highly efficient, 16.3% more efficient than the basic compressor layout.