Consistent comparison and thermo-economic optimisation of grid-scale thermo-mechanical energy storage technologies

Thermo-mechanical energy storage technologies can play an important role in low-carbon energy systems by storing surplus renewable energy and discharging when needed, with several promising variants currently under development for grid‑scale applications. Relevant technologies include adiabatic compressed-air energy storage, liquid-air energy storage, and pumped-thermal electricity storage. In this work, comprehensive thermo‑economic optimisation models are developed for these three technologies, using a unified framework based on consistent performance and cost assumptions. This approach allows for a consistent comparison between these leading thermo-mechanical energy storage technologies. The optimisation and comparisons are performed for a range of nominal discharge power ratings and charging and discharging durations to capture scale effects. Results show that adiabatic compressed‑air energy systems achieve the lowest capital costs but rely on access to available, suitable large underground caverns to store the air. Liquid‑air and pumped‑thermal electricity storage systems do not face such geographical constraints. Between these two options, the former exhibits lower costs at low power ratings (as low as 380 v. 470 $/kWh for 10-MW systems), while the latter is more economical at high nominal power (as low as 160 v. 205 $/kWh for 100-MW systems) and offers a higher energy density (up to 72 v. 30 kWh/m3 for 100-MW systems). Overall, minimum energy capital costs of 124 $/kWh at power capital costs of 1120 $/kW can be achieved for 100‑MW compressed-air systems, which is highly competitive with other grid‑scale energy storage technologies such as electro-chemical batteries, hydrogen storage or power‑to‑gas.