Performance mapping of packed-bed thermal energy storage systems for concentrating solar-powered plants using supercritical carbon dioxide

•Charging-discharging combined efficiency of a packed-bed thermal energy storage system (TES) operating with s-CO2.•Axially discretized transient model of a TES system coupled to a power cycle.•Determination of optimal geometrical features for the TES system. Thermal energy storage is extremely important to power plants that rely on intermittent heat sources. Additionally, the interest in power cycles operating with supercritical carbon dioxide (s-CO2) is increasing recently. Therefore, this study investigates the performance of a packed-bed thermal energy storage (TES) system using s-CO2. The 1-D computational porous medium-based model accounts for the heat exchange between the solid matrix and heat transfer fluid through a two-temperature formulation, thus allowing the calculation of the pressure drop and the heat loss to the environment, which are derived from the fluid flow through the thermal energy storage tank. The thermal-hydraulic analysis investigates, from parametric and optimization standpoints, the effects on the performance of the TES system of design and operational parameters, such as the storage tank volume and length/diameter ratio, porous medium particle size and porosity, charging and discharging mass flow rates, charging temperature, and the charging-discharging cycling. The results clearly suggest design trends for s-CO2-based systems, as well as show that not only the thermal-hydraulic charging-discharging combined efficiency of the TES unit is highly dependent on the above-mentioned parameters, but also and more importantly, that it can be optimized with respect to dimensional and operational parameters.