THE SODIUM-SULFUR BATTERY FOR UTILITY-SCALE APPLICATIONS

SUMMARY The advancement of NAS battery electrical energy storage technology has added the new tool of "storage" to electrical distribution networks. Until now, system planners were locked into an equation that required electrical power generation to be coincident with consumption. This functionality combined with high-speed response of the NAS battery system is not limited to load-leveling, but can also work well in the independent grid. Moreover it is useful for the stability of renewable energy resource output. Generally speaking it has been difficult for the conventional emergency generator to keep good power quality in a closed grid because the generator output cannot follow the demand change quickly. But we have demonstrated that NAS battery system could keep the stable power supply to the loads containing the induction motor in an independent grid. This demonstration shows that the NAS battery system can control the current quickly by the ac/dc converter and we keep the stability on the voltage comparatively even when an induction motor starts in the closed grid. This result shows that the realtime, fast response of the NAS battery system maintained good power quality in these grids. Another important result was on the wind power generator with the NAS battery system. It is impossible to control the wind power generator output because it depends on the wind. So the sudden change of the output give a bad influence to the power quality, voltage and frequency. But our demonstration shows that 500 kW wind power generator output fluctuation is suppressed by the 400 kW NAS battery system through high-speed charge/discharge control. Now the advanced project is on going. This project consists of 51,000 kW wind power generator with 34,000 kW NAS battery system. This project will not only demonstrate the wind power stabilization by the NAS system, but also demonstrate storing energy generated by wind at night for dispatch at constant power during the daytime. Once its effectiveness in stabilizing and shaping wind generation is confirmed, we expects the Hybrid Wind-NAS system will be widely deployed. The NAS batteries described in this article are superior to conventional alternatives in terms of durability, reliability, stability and they are expected to be progressively introduced in the future as an important and highly versatile tool for effectively utilizing clean electrical power resources, as well as for efficient use of existing distribution networks.