Batteries to store wind energy

Scientific American reports that Xcel Energy, a Minneapolis-based utility company, has started to test a new technology to store wind energy in batteries. The company is currently trying it in a 1,100 megawatts facility of wind turbines in Southern Minnesota. The company started this effort because ‘the wind doesn’t always blow and, even worse, it often blows strongest when people aren’t using much electricity, like late at night.’ It has received a $1 million grant from Minnesota’s Renewable Development Fund and the energy plant should be operational in the first quarter of 2009. And if this project is successful, the utility expects to deploy many more energy plants before 2020 to avoid more polluting energy sources. …

You can see two pictures on the left. The top one represents workers lifting a battery module into place. (Credit: S&C Electric Company) The picture below is a schematic of one of these sodium-sulfur batteries. “The battery is made up of twenty 50-kilowatt modules. It is roughly the size of two semi trailers and weighs approximately 80 tons. The battery is able to store about 7.2 megawatt-hours 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. Fully charged, the battery could power 500 homes for over 7 hours.” (Credit: Xcel Energy)

So where are these batteries coming from? “The energy storage in question — a series of sodium-sulfur batteries from NGK Insulators, Ltd. — can store roughly seven megawatt-hours of power, meaning the 20 batteries are capable of delivering roughly one megawatt of electricity almost instantaneously, enough to power 500 average American homes for seven hours.

Here is a quote from Frank Novachek, director of corporate planning for Xcel Energy: ‘Over 100 megawatts of this technology [is] deployed throughout the world. The batteries ’store wind at night and they contract with their utility to put out a straight line output from that wind farm every day.’”

These batteries are efficient, but also expensive. They cost “$3 million per megawatt plus millions for start-up and testing. ‘Right now, they’re a little too expensive,’ Novachek says. But ‘it’s getting in the ballpark where it looks like the economics might be there. Testing will help us understand the value.’ So far the battery has been through five charging and recharging cycles and testing will continue through next year, Novachek says.”

Here is a link to a Xcel Energy press release from February 28, 2008, “Xcel Energy launches groundbreaking wind-to-battery project,” which provides additional details about the project. “The project will take place in Luverne, Minn., about 30 miles east of Sioux Falls, S.D., with the battery installation beginning this spring adjacent and connected to a nearby 11-megawatt wind farm owned by Minwind Energy, LLC. S&C Electric Company will install the battery and all associated interconnection components.”

Finally, if you’re interested in this project, please read the two following documents from Xcel Energy.

• Wind Storage Research and Experiments (PDF format, 21 pages, 714 KB)
• Wind-to-battery Project (PDF format, 2 pages, 1.98 MB), from which the above images have been extracted

Sources: David Biello, Scientific American, December 22, 2008; and various websites

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