Various embodiments of the teachings herein include an energy management system for a building having power consumption devices, power generation devices, and power storage devices. An example includes: a monitoring unit to acquire information about power generated by the power generation devices, about power consumed by the power consumption devices, and about a respective state of charge of the power storage devices; a management unit to derive information about a flexibility of the power demand of the power consumption devices deployed in the building based on the information acquired by the monitoring unit; and an optimization unit to optimize the power allocation of the power produced by the power generation devices to the power consumption devices and/or to the power storage devices based at least in part on the derived flexibility information of the power demand.