Analytical modeling of advanced adiabatic compressed air energy storage: Literature review and new models

We review the literature on analytical models of advanced adiabatic compressed air energy storage plants with isochoric reservoirs, with a focus on the insights that can be extracted from the models. The review indicates that models for plants with adiabatic reservoirs, adiabatic turbomachinery, and without throttling is missing from the literature. We proceed to derive such models, assuming that the plant is operating at the quasi-steady state, that air can be treated as a calorically and thermally perfect gas, and that thermal-energy storage units are free of thermal and pressure losses. The models result in closed-form expressions for key performance indicators like the plant efficiency and volumetric energy density in terms of component efficiencies and pressure ratios. The derivation of these expressions rests on approximating integrals involving simultaneous temporal variations of temperature and pressure. The approximation leads to relative errors with magnitudes smaller than 1%. The models show that the compression and expansion work, the plant efficiency, and the maximum process temperature exhibit minima. The models also show that for a given non-dimensional storage capacity and maximum reservoir pressure, the maximum efficiency of plants that minimize the maximum process temperature is approximately equal to the minimum efficiency of plants that maximize the efficiency. For a two-stage plant with a diabatic cavern and diabatic thermal-energy storage units, our analytical model predicts the volumetric energy density to within 4.76%, indicating that it is accurate enough to be used for initial plant design.