A preconditioned air system for cooling an interior cabin space of a parked aircraft includes a thermal energy storage unit, which contains a thermal energy storage medium for storing cooling capacity. During use, a ground-based air-cooling unit is placed in thermal communication with the thermal energy storage medium. The ground-based air-cooling unit draws upon cooling capacity that has been stored previously within the thermal storage medium for cooling the interior cabin space. Storage of cooling capacity is performed during off-peak demand times and/or during low power cost times. System modularity supports cooling of variously sized aircraft even under extreme temperature conditions.