An electrical power supply system is managed by a master management system external to the supply system. The system includes a power generator generating electric power using renewable energy, a battery storing electric power generated by the power generator, and a power output device outputting power from the power generator or the battery. The system also includes a charge and discharge controller acquiring generated power data from the power generator, transmitting the generated power data to the master management system, computing a target output value for output from the power output device, and controlling charge and discharge of the battery such that the target output value is outputted from the power output device. The charge and discharge controller receives charge and discharge instruction signals from the master management device, and initiates or terminates the charge and discharge of the battery based on the charge and discharge instruction signals.