From short-term buffering to long-duration time-shifting: Evaluating the dynamic roles of compressed air and CO2 Carnot Battery energy storage in future power systems

To elucidate the multi-timescale dynamic adaptability of thermo-mechanical energy storage in renewable-dominated grids, this study developed dynamic simulation models for an Adiabatic Compressed Air Energy Storage (A-CAES) system and a CO2 Carnot Battery system. By coupling these models with real-world meteorological boundary conditions, the transient thermodynamic behaviors and fluctuation smoothing mechanisms were rigorously evaluated. The results indicated that the A-CAES system, leveraging the volumetric effect of air storage, excelled in short-term buffering by attenuating source-side power fluctuations of up to ±31.66%, achieving a power fluctuation smoothing rate of 59.05% and a high-frequency noise suppression rate of 84.27%. However, sliding-pressure operation induced thermodynamic mismatch and significant exergy destruction, causing the stage expansion ratio to decay continuously from an initial value of 4.45. This reduced the effective single-stage temperature drop from approximately 200 K to nearly 60 K. In contrast, the CO2 Carnot Battery functioned as a thermal buffer, utilizing the substantial thermal inertia of molten salt to achieve deep energy time-shifting. Statistical analysis revealed the Carnot Battery's dual adaptability: it mitigated high-amplitude power fluctuations in wind-dominated winter scenarios with a power fluctuation smoothing rate of 98.18% and a high-frequency noise suppression rate of 99.53% (attenuating spectral energy by an average of 2.34 orders of magnitude). In solar-dominated summer scenarios, it reshaped the probability distribution of power output—reducing the source-side pulse kurtosis from 4.76 to 0.70—while maintaining seasonal round-trip efficiencies between 58.88% and 66.40%. These findings clarify the complementary roles of the two technologies, positioning A-CAES for rapid volatility suppression and CO2 Carnot Battery for large-scale, long-duration accommodation of renewable energy.