Apparatus and method for controlling a building power system

is proposed a control unit for a system with an air conditioning unit, a generating unit for generating electric energy and an energy storage for storing electrical energy, which is in communication with a network connection point for feeding or receiving electrical energy to or from an external power supply. The control unit is configured to control the air conditioner, the generator unit and the energy storage device together in response to at least one condition associated with the supplied or consumed electric energy current and / or voltage. In addition, a corresponding control method and a building energy system are proposed.