Operation of a 100-kilowatt-hour sodium-sulfur battery

A 100-kWh Na-S battery has operated for over one year. It is modularized, with four independently heated compartments containing two 64-cell submodules each. The 512 cells have an energy capacity of 286 Wh each, and are connected in parallel within a submodule. The eight submodules are connected in series to provide a nominal 16 Vdc battery voltage. The battery is rated at 1500 A discharge for 5 h, 1080 A charge for 7 h. Initially, the battery delivered 103 kWh and its round-trip efficiency was 74.6 percent. Control system faults necessitated repairs to two modules, which required freezing and thawing of those cells. These operations were partly successful, with one module being unaffected by the faults and repairs. Initial repairs to the second module were less successful, and after two further repair cycles the battery was operated without it.