Development of a compact sodium sulphur battery

A 6 MW (48 MWh) sodium-sulphur battery system consisting of 240 modules, the largest such system in the world, has been working properly at Tsunashima substation of Tokyo Electric Power Co. Inc. since January 1998. The system has been proved to function as an electric energy storage system for load levelling. The construction and operating performance of the sodium-sulphur battery cell, module and system are described in this article. Evaluation of the durability and safety of the cell and module are also discussed.