Abstract: A power flow control system including an integrated circuit having a mechanism for determining an amount of energy storage required for power source devices and a mechanism for controlling power flow delivery between the power source devices. A power flow control system also including more than one power source device in electrical connection with the power flow control system. An efficient hybrid vehicle, including the power flow control system integrated in the hybrid vehicle, and more than one power source device in electrical connection with the power flow control system and operatively connected to the hybrid vehicle. A method of controlling power flow in a vehicle, including the steps of determining the amount of energy storage required for power source devices, and controlling power flow delivery between the power source devices. Power flow control systems and methods of using for fuel cell and battery combinations and battery and super-capacitor combinations.