Xcel Energy soon will begin testing a cutting-edge technology to store wind energy in batteries. It will be the first use of the technology in the United States for direct wind energy storage.

Integrating variable wind and solar power production with the needs of the power grid is an ongoing issue for the utility industry. Xcel Energy will begin testing a one-megawatt battery-storage technology to demonstrate its ability to store wind energy and move it to the electricity grid when needed. Fully charged, the battery could power 500 homes for more than seven hours.

"Energy storage is key to expanding the use of renewable energy," said Dick Kelly, Xcel Energy Chairman, president and CEO. "This technology has the potential to reduce the impact caused by the variability and limited predictability of wind energy generation."

Xcel Energy has signed a contract to purchase a battery from NGK Insulators Ltd. that will be an integral part of a project. The sodium-sulfur battery is commercially available and versions of this technology are already being used in Japan and in a few U.S. applications, but this is the first U.S. application of the battery as a direct wind energy storage device.

The 20 50-kW battery modules will be roughly the size of two semi trailers and weigh approximately 80 tons. They will be able to store about 7.2 MWh 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 supplement the power flow.

The project will take place in Luverne, Minnesota, about 30 miles east of Sioux Falls, South Dakota, with the battery installation beginning this spring adjacent and connected to a nearby 11-MW wind farm owned by Minwind Energy, LLC. S&C Electric Co. will install the battery and all associated interconnection components. The battery is expected to go on-line in October 2008.

Partners in the project with Xcel Energy include the University of Minnesota, the National Renewable Energy Laboratory, the Great Plains Institute and Minwind Energy, LLC. Xcel Energy is testing emerging technology and energy storage devices as part of its overall Smart Grid strategy, which modernizes and upgrades the grid to allow for easier integration of renewable energy sources.

The project has been selected to receive a $1 million grant from Minnesota's Renewable Development Fund, pending Minnesota Public Utilities Commission approval this spring.