Minnesota wind-farm battery going back online

• Xcel Energy plans to restart a large battery at a Luverne wind farm that stores electricity and releases it as needed on the grid.
  
• The only battery in Minnesota large enough to store electricity from wind turbines is going back into operation after a 15-month shutdown and overhaul to reduce the risk of fire.
  
• Xcel Energy Inc. installed the $4.7m battery in 2008 next to a wind farm and operated it safely for more than two years. The sodium-sulfur (NaS) battery was shut down in October 2011 on the advice of its Japanese manufacturer after a similar unit caught fire there.
  
• Now, the Minneapolis-based utility says, the Luverne battery has been rebuilt by manufacturer NGK Insulators of Nagoya and is likely to be back in service by February.
  
• The 1 MWh battery can store enough electricity to power 500 homes for 7.2 hours.
  
• One shortcoming of some new battery technologies is the fire risk. After the September 2011 battery fire in Japan, NGK halted production of the batteries and advised customers, including Xcel and 19 other customers in North America, to stop using them. NGK later determined that a faulty cell had leaked molten material, triggering a short circuit and fire.
  
• NGK has addressed issues with its sodium-sulfur technology. NGK said it has redesigned its grid-scale batteries, adding fuses and insulation. Aki Sawafuji, a company spokesman, said the company completed replacing or refurbishing all of its North American customers' batteries in January and has resumed production.
  
• "We believe that the measures we have taken are sufficient to allay uncertainties about the future safety of the technology," Sawafuji said in an e-mail.

Source: Star Tribune / Data compiled by Renewable Analytics LLC.