Xcel Energy, (NYSE: XEL)in partnership with the University of Minnesota, the National Renewable Energy Laboratory and the Great Plains Institute, will soon begin testing a one-megawatt sodium-sulfur battery storage system to demonstrate its ability to store wind energy and dispatch it to the electricity grid when needed.
Fully charged, the batteries could power 500 homes for six and one-half hours. Xcel Energy will purchase the batteries from NGK Insulators, Ltd. that will be an integral part of the project. The sodium-sulfur battery is commercially available and versions of this technology are already being used in Japan and in a few US applications, but this is the first U.S. application of the battery as a direct wind energy storage device.
The 50-kilowatt battery modules, 20 in total, will be roughly the size of two semi trailers and weigh approximately 60 tons. They will be able to store about 6.5 megawatt-hours of electricity, with a charge/discharge capacity of one megawatt. When the wind blows, the batteries are charged. When the wind calms down, the batteries can be used to supply energy to the grid as needed.
"Energy storage is key to expanding the use of renewable energy. This technology has the potential to reduce the impact caused by the variability and limited predictability of wind energy generation."
-- Dick Kelly, Xcel Energy chairman, president and CEO.
The project will take place in Luverne, Minn., with the battery installation beginning this spring adjacent to a nearby 11-megawatt wind farm owned by Minwind Energy, LLC. Testing will begin in October and is expected to last up to two years.
Commercial projects are now underway that use flow batteries, compressed air energy storage, thermal energy storage, pumped hydro, and sodium sulfur batteries for energy storage in connection with renewable energy projects. American Electric Power (AEP) is also using NaS batteries in a couple of their systems, but not in connection with wind power. While not enough experience has been gained with any of these technologies to make any decision as to which technology is best under what conditions, pumped hydro and sodium sulfur batteries are the most well proven and thus seem to be the first choice of electric utilities. Thermal storage is gaining acceptance for use with thermal solar systems, the only energy technology that it is suitable for use with. As Mr. Kelly stated, energy storage is essential to widespread use of renewable energy technologies.