Xcel to use massive batteries to store wind-generated power 

The problem with electricity generated from wind turbines is, the power can fluctuate. Xcel Energy says it’s got a way to even out the flow – an 80-ton battery the size of two semi-trailers.

The Minneapolis-based utility said Thursday that it will begin testing a sodium-sulfur battery being used in Japan to even out the flow of electricity between windy days and nonwindy days.

Xcel plans to put 20 50-kilowatt batteries in Luverne, Minn., about 30 miles east of Sioux Falls, S.D., this spring and connect them to an 11-megawatt wind farm owned by Minwind Energy. The batteries are expected to go online in October.

When the wind is blowing, the batteries will charge, and when the wind diminishes, the batteries – which can discharge one megawatt of power – will supplement the flow of electricity to Xcel.

Xcel can handle the fluctuations in the 1,000 megawatts of wind energy it currently receives from the state’s wind farms, but by 2020, it must derive 30 percent of its generating power from a renewable resource such as wind. That would require about 3,900 megawatts of wind power, a load Xcel Energy corporate planning director Frank Novachek described as “considerable.” One megawatt powers as many as 1,000 homes.

“We’re trying to stay ahead of the curve, and we think this is the technology that can help us to that,” Novachek said.

The batteries would be tested for two functions, Novachek said. First, can they allow the wind farm to store energy collected from an off-peak time, such as at night, to be used on the grid during the day? Second, can the batteries help stabilize the transmission system from the variability of wind? The problem with wind isn’t that it blows and stops, but that it varies.

If the batteries pass the tests, they may allow wind farms to store power during an off-peak time and then sell it during peak hours for more money, such as on a hot summer afternoon when air conditioners are running, Novachek said.

While two other U.S. utilities use the batteries to supplement peak power needs, Xcel said it would be the first to use them for a wind project.

Numerous studies have shown that Xcel can handle the variability of wind power on its system even when it reaches its 2020 requirements, but the batteries could have longer-term implications, said Michael Noble, executive director of Fresh Energy, a St. Paul-based nonprofit advocacy group for renewable energy.

They might enable Xcel to get 40 percent or even half of its power in the future from wind, he said. They also might mitigate the need for more natural gas-fired power plants for peak usage times, he added.

“It’s really looking over the horizon,” Noble said. “It’s a good long-range thing to be working on.”

The batteries can last for 15 years and are safe, despite operating at a temperature of 572 degrees Fahrenheit, Novachek said. They go dormant if they cool down too much, he said.

The heat means Xcel won’t have to give them a jump-start in the dead of winter, he added.

The project was slated to receive a $1 million grant from Minnesota’s Renewable Development Fund, pending approval from the Minnesota Public Utilities Commission this spring.

Leslie Brooks Suzukamo
Pioneer Press
February 28, 2008

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