The NAS battery: a multifunction energy storage system

This paper presents an overview of the first U.S. demonstration of stationary sodium sulfur (NAS) battery energy storage technology hosted by the American electric power (AEP). The NAS batteries are supplied by NGK insulators, Ltd. in Japan. ABB, Inc. of New Berlin, Wisconsin supplied the power conversion system that integrates direct current (DC) from the NAS battery with the alternating current (AC) of the power grid. Other partners in the demonstration include the Tokyo electric power company (TEPCO), department of energy/Sandia national laboratories and EPRI. Testing was performed at ABB and supported by NGK and AEP's measurement and analysis team. Testing took one month to complete and used advanced measurement and recording equipment. In conclusion, the acceptance testing of the unit verified the functionality and grid compatibility of the system and the reliability of the protection mechanisms. The measured data were used to validate system performance and analyzed to recommend further improvements especially on the system dynamics, optimum usage of the energy stored in the batteries and reliability.