A renewable power system according to the exemplary embodiment includes a renewable power plant (121), a controllable plant (123) and an energy management system (128) which keeps an energy schedule within a certain tolerance in the next k (an integer greater than or equal to 1) steps by using a method that includes an optimization algorithm for a total power output shape within a step, and schedule changing algorithm for changing the energy schedule after the next k steps to keep a needed capacity of the plant regarding power and energy small. By keeping the energy schedule within a certain range for a renewable power plant combined with controllable plant, it is possible to keep the needed power and energy capacity of controllable plant small and to guarantee favorable total power output shape.