NOVELTY - The system has an electricity price monitoring portion provided to collect electricity price information from an electric grid (200). An electricity charge amount monitoring portion is provided to collect electricity charge amount information of battery (10) of charging and discharging system. A charging and discharging portion (340) is provided to selectively perform one of charging the battery and discharging battery based on determination made by charge and discharge determination portion.    USE - Charging and discharging system for solar light power generator in real-time pricing environment used by smart grid.    ADVANTAGE - The billing can be effectively carried out depending on the charging and discharging of electricity. The charge and discharge converter is provided with stable performance by which both charging and discharging can be carried out. The electricity is purchased from electric grid such as smart grid and is sold to the electric grid, based on the real-time electricity price information and the charge information of the battery. Thus, the operation of the charging and discharging system can be improved, so that user of the charging and discharging system is allowed to enjoy marginal profits.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) duplex converter for charging and discharging electricity into/from battery of charging and discharging portion of charging and discharging system;    (2) method of charging and discharging electricity into/from battery of charging and discharging portion of charging and discharging system; and    (3) computer readable recording medium storing program for charging and discharging electricity into/from battery of charging and discharging portion of charging and discharging system.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of the charging and discharging portion.    Battery (10)    Electric grid (200)    Charging and discharging portion (340)    Solar light power generator (400)    Transformer (TR)