The first megawatt-class sodium sulfur (NaS) battery placed in service in North America was installed this June in Charleston, W.Va. The 1.2-MW system-comprising the battery and a bidirectional inverter-can be discharged during the day to provide 7.2 MWh of on-demand power for shaving peak loads and be recharged at night. It's no longer true that electricity can't be stored, except in small quantities.