Updated by Staff

Minneapolis-based Xcel Energy says it is pleased with preliminary results of a test project in Minnesota for large-scale battery storage of wind energy  – and possibly, in the future, solar electricity.

The results show that it works, according to the multistate power company.

Several studies are under way in the United States, and more are ongoing in other countries, on using batteries to help integrate the intermittent and variable electricity production from solar and wind installations into the
steady current flow of electricity grids.

Among them is the sodium-sulfur battery system shown in photo being installed in Presidio, Texas. It is the largest such energy storage array in the United States. (Photo: Electric Transmission Texas)

Most solar technologies generate electricity only in the daytime (some are able to extend production for hours after sundown), and winds are often strongest and steadiest at night.  

In October 2008, the multistate utility company began testing a 1-megawatt battery storage system to store wind energy and transmit it to the grid when needed. The company says this is the first use of the technology in the United States for direct wind-energy storage.

“We have proved that this technology can perform the functions of storage that we were looking for to help us manage the variability of wind energy on our operating system,” said Frank Novachek, Xcel Energy’s director of corporate planning, in a news release. “The success of this technology is important to both Xcel Energy – the nation’s leader in wind power distribution – and our customers, and we are greatly encouraged by these results.”

Preliminary results, Xcel said, show the battery system can:

• Effectively shift wind energy from off-peak to on-peak availability;

• Reduce the need to compensate for the variability and limited predictability of wind generation;

• Provide voltage support, which contributes to grid reliability;

• Assist the regional electricity market by responding to real-time imbalances between generation and load.

The results also indicate that the technology could be applicable for solar energy, according to Xcel.

Testing will continue in order to determine the battery system’s ability to help integrate larger proportions of wind energy with the grid. The second phase of the study will also look at the cost-effectiveness of this approach. A final report is expected in the summer of 2011.

The project is taking place in Luverne, Minn., about 30 miles east of Sioux Falls, S.D. The battery system is connected to a nearby 11-megawatt wind farm owned by the company Minwind Energy.

Altogether, Xcel Energy said, the 20 50-kilowatt battery modules are about the size of two semi-trailers and weigh about 80 tons. They can store about 7.2 megawatt-hours of electricity, and when fully charged, could power about 500 homes for more than seven hours.

Xcel Energy purchased the sodium-sulfur battery system from NGK Insulators Ltd.  Other versions of the technology are in use in the United States and other countries, but Xcel Energy said this is the first use of it to directly store wind energy.

Along with NGK Insulators and Minwind Energy, other participants in the project include S&C Electric, the University of Minnesota, the National Renewable Energy Laboratory, Gridpoint, and the Great Plains Institute.

Xcel Energy said it is testing emerging technology and energy storage devices as part of its “Smart Grid” strategy, which involves modernizing and upgrading the grid to allow for easier integration of renewable energy sources.

The project received a $1 million grant from Xcel Energy’s Renewable Development Fund.