A network system is provided. The network system includes: at least one component of an energy supply unit supplying energy and an energy management unit managing the energy supply unit. An amount of energy used or energy charge of the energy supply unit is adjustable. An amount of energy used or energy charge when the component is controlled on the basis of information related to at least usage charge may be less than that when the component is controlled not on the basis of the information related to at least usage charge. Also, the energy supply unit has a power saving mode to determine a driving method or a driving time of the energy supply unit on the basis of the information related to energy charge.
