Sodium-sulphur battery system and driving method thereof

The present invention relates to an electric power storage system used for flattening the load of an electric power line and shifting the peak of the electric power line and, more particularly a sodium-sulfur battery system and a method of operating the sodium sulfur battery system and an electric power line system using the sodium-sulfur battery system. There are provided a sodium-sulfur battery system suitable for shifting the peak of an electric power line, and a method of operating the sodium-sulfur battery system and an electric power line system using the sodium-sulfur battery system.In a sodium-sulfur battery system comprising a battery module having a sodium-sulfur battery contained in a thermal insulation container, an amount of peak-shift of an electric power line, which can be performed by the battery module, is calculated using a daily load characteristic of the electric power line and a discharge characteristic of the battery module, and an allowable amount of heat generation in battery and an allowable amount of discharge, and discharge of the battery module is controlled using the calculated result.The peak-shift of an electric power line can be effectively performed without deteriorating the reliability of the sodium-sulfur battery, and the efficiencies of the sodium-sulfur battery system and an electric power line system using the sodium-sulfur battery system can be kept high.