Life-cycle exergetic efficiency and CO2 intensity of diabatic and adiabatic compressed air energy storage systems

Abstract

This study uses the concept of exergy-return on exergy-investment (ERoEI) to evaluate the life-cycle exergetic efficiency and CO₂ intensity (grams CO₂ per MJ of electricity) of (diabatic and adiabatic) compressed air energy storage (CAES) systems. Several CAES configurations are assessed under defined system boundaries, including diabatic systems powered by methane (CH₄) or hydrogen (H₂), and adiabatic system with a thermal energy storage (TES) facility.

The results show that conventional (diabatic) CAES system powered by natural gas has the lower exergetic efficiency and higher CO₂ intensity compared to adiabatic CAES due to the heat dissipation during compression stage and additional fuel requirements for reheating the air during expansion. Integrating carbon capture and storage (CCS) plant with conventional diabatic CAES can nearly halve the CO₂ intensity for electricity generation although the additional exergy investment for the CCS process reduces the exergetic efficiency of the system. Transitioning to green H₂ (produced from low-carbon electricity) as the primary turbine fuel in the diabatic CAES results in a 65–76 % reduction in CO₂ intensity. However, the average exergetic efficiency of system decreases by around 10 %, mainly due to the substantial exergy investment associated with hydrogen production. It is also found that the adiabatic CAES system integrated with TES demonstrates the highest thermodynamic and environmental performance. When 100 % of compression heat is captured and reused during discharge phase, the system reaches ERoEI values up to 61 % with CO₂ intensity of 12–26 g CO₂ per MJe.

Disclaimer: The results and performance metrics presented in this study are based on modelled scenarios and literature-derived parameters under defined system boundaries. Actual performance of CAES systems may vary depending on site-specific conditions, technology maturity, and operational configurations. All efficiency values, CO₂ intensity estimates, and comparative assessments should be interpreted within the context of the assumptions and limitations described herein. This study does not constitute a commercial endorsement or performance guarantee. The authors have made every effort to ensure accuracy but accept no liability for decisions made based on this analysis.