Back in October 2008, Xcel Energy started an innovative study in which it installed a 1-megawatt (MW) capacity battery (20 50-kW NGK Insulator batteries) near an 11-MW wind farm owned by Minwind Energy, LLC. The battery was supposed to store, when possibly, the wind energy and release it to the grid when necessary. For the past 21 months the utility has been collecting data and this week it released preliminary results.

The bottom line? It works.

The test was the first use of the technology in the United States for direct wind energy storage.

The preliminary test results are good and show that the battery can do the following:

  • 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 resources.
  • Support the transmission grid system by providing voltage support, which contributes to system reliability.
  • Support the regional electricity market by responding to real-time imbalances between generation and load.

Results also indicate that this technology may be applicable for solar energy. The complete report is available at Battery Energy Storage Click on: Milestone #5.

Xcel will continue with testing. Phase II of the study will also assess the potential value of the various battery-system functions and determine the potential cost effectiveness of the technology. A final report is expected in summer 2011.  

The gigantic batteries are roughly the size of two semi trailers and weigh approximately 80 tons. They are able to store about 7.2 megawatt-hours of electricity, with a charge/discharge capacity of one megawatt.

Xcel said that the sodium-sulfur battery is commercially available and versions of this technology are in use elsewhere in the U.S. and other parts of the world, but this is the first U.S. application of the battery as a direct wind energy storage device.

In addition to NGK, partners in the project with Xcel Energy include: S&C Electric, the University of Minnesota, the National Renewable Energy Laboratory, the Great Plains Institute and Minwind Energy, LLC, and Gridpoint.

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