A life-size lab chases the wind

Earlier this year, scientists offered a novel approach to boost the output of electric wind turbines: Coat the blades with a ribbed film that mimics shark skin.The experimental film made by 3M Co. worked well in a wind tunnel, reducing drag on turbine blades the same way sharks' ribbed skin helps speed them through water. But researchers in Minnesota initially lacked a place to test the concept in the real world.

"There are all these turbines around, but it is not easy to go to a wind farm and tell that owner, 'I want to turn off your turbine. I want to try something,'" said Fotis Sotiropoulos, a professor of civil engineering at the University of Minnesota and head of its Eolos Wind Energy Research Consortium.

Today, Sotiropoulos no longer has to ask. The university last month finished building a $5.5 million wind turbine at UMore Park in Rosemount that is the centerpiece of its wind energy research program, named after the Greek god of wind.

Minnesota, an early leader in developing wind farms, is now poised to become a national center for wind energy research. Only one other U.S. university and two national labs have large, working wind turbines for research.

Wind energy has been a growth industry, driven by tax credits and renewable energy mandates. The equivalent of 10 million U.S. homes are powered by

wind, and that will grow if states like Minnesota stay committed to getting 25 percent of electricity from renewable sources.

Sotiropoulos, who also directs the St. Anthony Falls Lab, said Eolos is attracting industry research partners, including Minnesota-based 3M, WindLogics and Barr Engineering, and fostering a new era of cooperation among industry, government and academic researchers. It's also training students to work in the industry.

The 2.5-megawatt Clipper Liberty was built with a federal stimulus grant awarded by U.S. Energy Department, which also is funding some of the studies. Other research money has flowed in, with prospects for more in the future.

Reducing drag with 'riblets'

One of the first studies planned at the turbine offers unusual promise.

G. Memo Izzi, leader of the ribbed film project at 3M's renewable energy division in Maplewood, said the company has for two decades researched films that mimic shark skin. Microscopic protrusions above the film's surface, called riblets, help air or water flow smoothly with less drag, he said.

In the 1990s, he said, 3M successfully tested such films to reduce drag on aircraft, but didn't launch a commercial product because of other technical challenges. The films also have been tested on racing yachts, including two winners of America's Cup.

"3M can make the material, but we can't test it," said Izzi, who gave a presentation about the project at a wind industry conference in May.

The company already has worked with the university to test the film in the St. Anthony Falls Lab wind tunnel. That partnership has evolved into the planned experiments at the UMore Park turbine. Izzi said scientists will study how and where to apply the film, which seems to work best on a blade's trailing surface.

The goal is to create a new 3M product offering an incremental boost in turbine efficiency. The film cut drag up to 6 percent in wind-tunnel tests, Izzi said. Multiplied across the all of the nation's wind farms, even a small increase in blade efficiency could reap large gains in power output.

As a bonus, the film could potentially make the blades less noisy, he added.

"It shows that to apply new technology to a new industry requires a strong partnership between the industry making the product and a research center where we can do very complex research studies," Izzi said.

Long research lists

Another early partner in the Eolos project is Clipper Windpower, the California-based wind energy company that supplied the turbine.

Clipper operates the Rosemount wind turbine from a monitoring and diagnostics center in Cedar Rapids, Iowa, where it also has a manufacturing plant. When the turbine is operating, electricity is sold to the grid.

The company also has its own list of planned research projects related to blade aerodynamics, turbine controls, gear box efficiency, energy storage, smart grid and acoustic performance.

Debarshi Das, manager of commercial technology for Clipper, said he will be particularly interested in whether efficiency research like the 3M coatings studies could allow turbines to operate at lower wind speeds, extending operating duration.