U of M chemical engineering professor Bill Smyrl will be testing the capabilities of sodium sulphur batteries used by Xcel energy to provide long-term storage for excess electricity generated by wind turbines in southwestern Minnesota.

Glen Stubbe, Star Tribune

Storing wind energy in a bottle

  • Article by: HILARY BRUECK
  • Special to the Star Tribune
  • May 4, 2008 - 5:36 PM

Growing up, Bill Smyrl loved visiting his aunt and uncle on their ranch in rural New Mexico. But when evening came and darkness fell, young Smyrl, now a University of Minnesota chemical engineering professor, thought twice before turning on a lamp. They lived too far out in the country to be hooked up to power-company lines, so they relied on a small-scale wind generator to keep the lights on.

Now that modern energy technologies have reached even the most remote of homes, Smyrl will be spending the next few years on a formidable task: harnessing that same rural wind -- even when it doesn't blow -- on a much larger scale than lighting up a ranch. This summer, he will begin testing how to store wind energy in large-scale chemical batteries.

In recent months renewable energy has been billed as the solution to many of the nation's problems as well as the cause of them. With record oil prices pinching budgets in small families and at big business, Congress and state legislatures are passing laws requiring ever-higher mandates on the percentage of energy that must come from renewable resources. Minnesota's measure, one of the toughest in the nation, requires power companies to get 25 percent of energy from renewable resources by 2025.

But a push into biofuels -- particularly corn-based ethanol -- is at least partly to blame for rising food prices and some food shortages around the globe.

By comparison, wind energy is largely welcomed, though it's done little to dent U.S. oil consumption. Power from wind is teetering at 1 percent of the nation's total energy. In Minnesota it is a healthier 4.6 percent, second only to Iowa in the percentage of energy derived from wind.

Figuring out how to harness wind, and store its energy, is going to be crucial as the country pushes for cleaner energy.

"Energy storage is key to expanding the use of renewable energy," said Dick Kelly, chairman and CEO of Xcel Energy Inc., in a February announcement that the company was partnering with the University of Minnesota on Smyrl's research. Xcel is the largest purchaser of wind energy in the country, significantly ahead of other utilities.

A wide range of ideas

While scientists are developing many creative schemes to store wind energy, most are either far-fetched or still years from completion. Some researchers hope to create hillside pumps, or compress air in enormous underground caverns, while others envision enormous flywheels spinning with the buzz of wind-generated energy until it is ready to be spat back out and used.

Two not-so-far-fetched technologies have emerged as more real and immediate possibilities -- storing wind energy in batteries, and using it to produce and store hydrogen.

The first, Smyrl's project, is a large-scale chemical battery, akin to a giant, more environmentally friendly and efficient version of a rechargeable dry-cell battery.

These batteries are inherently different from the typical lead-acid ones in vehicles. The batteries are relatively huge -- each one about the size of two semitrailer trucks. They are around 10 percent more efficient than traditional batteries at transferring the energy they store and are greener, because they don't have any heavy metal in them.

Summer research will be housed on a 10-megawatt wind farm in Luverne, Minn, where around a dozen windmills will be spinning on calm and windy days alike to test the batteries resilience.

With the help of electronics, researchers will condition the batteries to withstand harsh and tumultuous winds, as well as calm days, in a way that won't wear their re-charge power out.

The batteries will be Smyrl's first try at wind energy storage, although he's been researching lithium ion batteries for over 15 years. He said the new sodium sulfur batteries, manufactured by a Japanese company, can operate at efficiencies of around 90 percent, because there's "only one reaction occurring in the battery."

He still wants to test the lifespan of the battery, and make sure it can withstand heavy pressures from the grid that distributes power from sources to customers. If demand for energy from the grid peaks when there is not a lot of wind blowing, the battery would go into a "deep discharge," and too many hair dryers and computers operating at once would nearly drain it of its power.

Smyrl will be watching to make sure recovering from that kind of pressure doesn't compromise the life or efficiency of the battery. If all goes well, he estimates that the huge new chemical batteries could be out to market in as little as five years.

But that's only 12 years away from the statewide deadline to have 25 percent of our energy from renewable sources. Even with such a short timetable, Smyrl says it is good to challenge power companies to explore ways to sustain alternative energies, regardless of the outcome.

"Why not have a challenge like that, even if we only came in at half [12 percent], that's a start," he said.

From wind to clean corn

The other storage possibility being researched here in Minnesota is storing hydrogen produced using wind energy. Hydrogen conversion is not only touted as an energy storage solution, but a gateway for hydrogen to be a clean-burning way to make crop fertilizer and transportation fuel.

For hydrogen storage, efficiency right now runs at only 42 percent, less than half of the chemical batteries. Smyrl said hydrogen is great, because it is efficient and you are "making chemicals locally ...[in] an environmentally benign technique." But the energy losses don't yet make it competitive with batteries for simple storage.

The element is essential to making a corn fertilizer -- anhydrous ammonia -- costs around $900 per ton in southern Minnesota. Right now Americans import about half its hydrogen-based fertilizer.

As a result, "our [biofuel] industry can't be considered completely domestic," said Mike Reese, who, as renewable energy director of the university's West Central Outreach Center, expects he'll be creating a more earth-friendly fertilizer for the Morris campus corn crops before next spring's seeding.

Reese says there's hope that, with renewable hydrogen production, fertilizer can be produced for grain and corn production without the use of natural gas or fossil fuels. "As we move toward reducing greenhouse gases, [and see] increased transportation cost for coal, wind energy is becoming more competitive," Reese said.

But the process of hooking up new wind energy to the grid can take years. The Midwest ISO, an independent nonprofit that manages the energy grid to make sure it will remain stable when new power supplies are added, has a large backlog for new wind farms.

"You can get and erect a [wind] farm in 18 months to two years, but to build a line can take seven years or longer," said Carl Dombek, spokesman for Midwest ISO, adding that most wind farms need more lines added, otherwise they overload the entire energy system. "It's great, it's clean, but it still takes the space."

Denmark, an age-old poster child for tapping into wind energy, is already well over the golden 20 percent threshold. And they do offer one solid piece of wind-savvy advice, as relayed by Rune Birk Nielsen of the Danish Wind Industry Association in an e-mail. "We have simply put up a lot of windmills," Nielsen said.

Hilary Brueck is a University of Minnesota student reporter on assignment with the Star Tribune.

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