Transient thermal behavior of above-ground CAES vessels: Experimental characterization, modeling, and system performance implications

Above-ground Compressed Air Energy Storage (CAES) offers critical siting flexibility for distributed energy storage but faces performance uncertainties due to complex thermal interactions between storage vessels and the dynamic ambient environment. Current thermodynamic models often oversimplify these interactions, leading to inaccurate efficiency predictions. This study addresses this gap through an integrated workflow combining experimental characterization, physics-based modeling, and system-level simulation. The transient thermal behavior of a steel CAES vessel was experimentally characterized via 10 independent operating conditions, with three repeated tests for each case, aiming to quantify air-wall heat flux and thermal inertia throughout charge-dwell-discharge cycles. Based on empirical findings, a novel physics-based composite lumped-parameter transient model was developed, explicitly coupling internal convection, wall thermal inertia, and dynamic environmental heat transfer. The transient model was strictly validated against experimental data at the single-vessel level across all dynamic phases. The model was then scaled up to evaluate a 500-tank storage array via deterministic calculation, with nominal turbomachinery parameters derived from published literature. Comparative analyses reveal that conventional models (e.g., adiabatic, isothermal, thin-wall) deviate significantly from actual performance. Specifically, under the baseline scenario, the thin-wall assumption significantly underestimates the system's round-trip efficiency (RTE) by an absolute margin of 5.71 percentage points (53.75% vs. 59.46%) relative to the proposed composite lumped-parameter transient model. The results demonstrate that neglecting wall thermal storage and environmental coupling leads to substantial design errors. The proposed workflow provides a baseline tool for the accurate prediction and optimal thermal management of distributed CAES systems.