Next spring Xcel Energy Inc., the state of Minnesota and a Virginia-based technology firm will test the first battery in the country capable of storing wind energy.

The breakthrough technology, which is the size of two semitrailer trucks stacked atop each other, was built in Japan and shipped to Luverne, Minn., where it will store electricity generated by the nearby Minwind Energy wind turbines. S&C Electric Co. expects the equipment will be completely installed by April.

The battery consists of a score of 50-kilowatt modules. When it is fully charged, the massive sodium-sulfur battery -- which weighs about 80 tons -- can store 7.2 megawatt-hours of electricity. That's enough to power 500 homes for about seven hours. It will cost more than $5.4 million to buy and install the battery and analyze its performance.

The technology could help allay critics of wind energy, who lament that no electricity is produced when there's no wind. If successful, the battery will store wind energy and release its power onto the electrical grid when the air is still.

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

Xcel, which invested $3.6 million in the project, expects the battery "to become very important to both us and our customers," Kelly said.

Xcel, the largest wind-energy producer in the country, is working to make it easier to integrate renewable energy onto the electrical grid as part of its "Smart Grid" strategy. It has a mandate to generate 30 percent of all its energy from renewable sources by 2020.

Xcel bought the battery from Japan's NGK Insulators Ltd. The batteries are used in Japan to store wind energy, and are used in a few nonwind applications in the United States.

"But this is the first U.S. application of the battery as a direct wind-energy storage device," Kelly said.

In addition to Xcel, the Minnesota Renewable Development Fund is contributing $1 million to the project. GridPoint, a power grid management firm based in Arlington, Va., kicked in $750,000. The University of Minnesota will analyze the battery system and grid connections. Other participants in the project include the National Renewable Energy Laboratory and the Great Plains Institute.

Xcel announced this month that it will develop 351 megawatts of new wind-energy production by December 2011 -- enough to power about 110,000 homes. The company said it plans to increase its current wind resources by more than 10 percent. The $900 million expansion includes a 201-megawatt project in southwest Minnesota's Nobles County, and a 150-megawatt project in Dickey and McIntosh Counties in southeastern North Dakota. Xcel has 1.2 million electricity customers in Minnesota.

Dee DePass • 612-673-7725