2B or Not 2B?

In search of an economical way to store wind power

Sometimes, when residents of Luverne, Minn., catch a glimpse of the dozen wind turbines sitting atop farmland a few miles outside of town, the towering white pinwheels look as if they’re barely moving. That’s because the biggest winds come sporadically, such as when storm fronts bear down, or between the hours of 12 a.m. and 4 a.m., when everyone is sleeping.

Up until recently, this has been something of a problem. The gusts that make Minnesota one of the richest sources of wind-based electricity in the U.S. are inconsistent and blow strongest at night, when energy is least needed and market prices for electricity are at their lowest.

But now, instead of simply dumping some of that excess nighttime power, Xcel Energy, the Minneapolis-based utility that buys the wind farm’s electricity output, is capturing it in 20 massive sodium-sulfur batteries situated in the prairielands several miles west of Luverne. Stacked inside two semitrailer-sized aluminum lockers, the batteries are capable of discharging 1 megawatt, enough to power 500 homes for seven hours.

Frank Novachek, Xcel’s director of corporate planning, says this demonstration project – funded in part by IonE’s Initiative for Renewable Energy and the Environment – allows Xcel to access that wind energy whenever it wants, whether for meeting unexpected demands or evening out electricity flows.

“It’s been up for about a year and a half and we’ve found that it does a great job of smoothing energy. Overall, it’s performed beautifully,” he says.

Xcel’s Wind-to-Battery (W2B) project is a $4.6 million bet on wind becoming a prime-time contributor to America’s electricity needs. A big player in renewable energy development, Xcel, whose service area extends south to Texas and New Mexico, gets more of its electricity from wind – some 8 percent – than any other utility company in the U.S. And that number is poised to go higher. Under state law, by 2020 the company is required to generate 30 percent of the electricity it supplies to Minnesota customers from renewable sources. In Minnesota, that’s going to mean lots of nocturnally spinning turbines.

Ned Mohan, a professor of electrical engineering in the University of Minnesota’s College of Science and Engineering, says batteries have the potential to dramatically boost the economic appeal of wind energy. “The promise with batteries is that you can buy it cheap, like at night, store it and then sell it high,” says Mohan, who is studying the economics of battery storage for Xcel. “You could store it in the Midwest when the wind is blowing and then supply it to Michigan, for instance, where prices are higher and there’s lots of demand.”

That’s the theory anyway. Xcel’s W2B test is promising, but it’s still just a test. Because industrial-scale, 80-ton battery installations are prohibitively expensive, you won’t see them popping up next to wind farms any time soon. According to Xcel’s Novachek, prices need to drop by at least 50 percent in order for batteries to become a viable option.

For this reason, batteries are just one of the possibilities the utility industry is considering as it plans for a future more reliant on renewable energy. Other technologies include storing electricity in devices called flywheels, upgrading transmission grids to better distribute and manage intermittent energy sources, and storing energy in electric vehicles. “If 10 percent of all Minnesotans had EVs, they could have that wind power trickle into the car battery at night,” says Michael Noble, executive director of Fresh Energy, a St. Paul­–based nonprofit promoting clean energy.

Novachek says Xcel remains open to all of these possibilities, but sees the greatest promise in battery storage. After spending $4 million on the Luverne project, the company is writing a check for another $1.5 million for a lead-acid battery trial near a solar testing facility in Aurora, Colo. Although sun-based power obviously doesn’t have wind’s nighttime issues, it’s even more unpredictable as an energy source, with outputs dipping every time the sun ducks behind the clouds.

As for the cost of batteries descending to more earthly levels, Novachek thinks it’s a matter of when, not if. “There are lots of companies out there doing interesting R&D, and they claim to have promises for reducing costs,” he says. And when those new, more efficient technologies evolve, Xcel will already have already made the investment to figure out how they work and how they can be best incorporated into a distributed electricity system.

MELANIE WARNER is a Boulder, Colo.–based freelance writer who covers food and green business. Her articles have appeared in the New York Times, Fast Company and Fortune, and online at BNET.

Xcel Energy


Stacked inside two semitrailer-sized aluminum lockers in southwestern Minnesota, massive sodium-sulfur batteries store wind energy on blustery days and discharge it as needed.