Electric energy saving system, electric energy saving method, electric power providing system, billing system and method for recharging electric car

PURPOSE: A power energy storing system a power energy storing method, a system for providing power for charging an electric vehicle, and a method and system for billing the power for charging the electric vehicle are provided to charge the electric vehicle by using renewable energy from an electric train. CONSTITUTION: An aerial wire(20) supplies power to an electric train(90). An energy storage device(10) receives and stores power energy from the aerial wire. A voltage of a three-phase four-wire power source(61) is rectified to a DC voltage by a transformer(62) and a rectifier(63). The rectified DC voltage is supplied to the electric train through the aerial wire. A part of the power energy includes regenerative power of the electric train connected to the aerial wire.