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The temperature and pressure variation limits within the cavern of a compressed air energy storage (CAES) plant affect the compressor and turbine works, the required fuel consumption and therefore the overall plant performance. In the present work, the thermodynamic response of adiabatic cavern reservoirs to chargeldischarge cycles of CAES plants are studied. Solutions for the air cavern temperature and pressure variations were derived from the mass and energy conservation equations, and applied to three different gas state equations, namely, ideal, real, and a self-developed simplified gas models. Sensitivity analyses were conducted to identify the dominant parameters that affect the storage temperature and pressure fluctuations. It is demonstrated that a simplified gas model can adequately represent the air thermodynamic properties. The stored air maximal to minimal temperature and pressure ratios were found to depend primarily on, both the ratio of the injected to the initial cavern air mass, and the reservoir mean pressure. The results also indicate that the storage volume is highly dependent on the air maximum to minimum pressure ratio. Its value should preferably be in between 1.2 and 1.8, where the exact selection should account for design and economic criteria.

A model on the air flow within aquifer reservoirs of Compressed Air Energy Storage (CAES) plants was developed. The design of such CAES plants requires knowledge of the reservoir air pressure distribution during both the charging and discharging phases. Also, it must assure air/water interface stability to prevent water suction during discharge. An approximate analytical solution for the pressure variations within the anisotropic reservoir porous space was developed, subject to the Darcy equation and for conditions of partially penetrating wells. Sensitivity analyses were conducted to identify the dominant parameters affecting the well pressure and the critical flow rate (water suction threshold). It is demonstrated that water coning is a factor that could severely limit the discharge air flow rate. A significant diminishment of that limitation and reduction of the pressure fluctuation can be achieved by enlargement of the air layer height and discharge period. Likewise, aquifers with larger horizontal permeability impose less restrictive critical flows. A conclusion on the preferred screen length could not be merely drawn from technological considerations, but should also involve important economic aspects.

The design of a Compressed Air Energy Storage (CAES) plant requires knowledge of the pressure and temperature variations within the reservoir, for expected sets of plant operation. In the current work, a closed form approximate analytical solution for the pressure variations, in porous media reservoirs, was derived for conditions of steady periodic isothermal radial gas flow. Two different expressions for the pressure variation were obtained, one as an infinite series and the other as an integral, where the latter is the computationally preferred solution. In order to evaluate the model accuracy, a finite difference numerical solution of the full nonlinear problem was developed. The accuracy of the analytical solution was confirmed through, both, error analysis and comparison against the numerical calculations. The analytical solution can be used to calculate the well pressure variations and the radius of the active region around the well. Examples of calculations are provided, and a parametric study is presented to demonstrate the sensitivity of the well pressure to pertinent parameters. The model could eventually yield improved CAES plant designs.