29 September 2011—Think about wind energy and chances are that fish and whales aren’t the first things that pop into your head. But the marine environment is just where some researchers are looking for inspiration to improve wind energy. They’re applying the concepts of biomimicry—using nature’s designs in their own—and it’s working, as evidenced by big strides in efficiency and output.
Janine Benyus, an expert on biomimicry who has been writing, consulting, and teaching on the topic for more than a decade, says that aping nature’s designs generally occurs on three levels. We can mimic form (the shape of a plant or an animal), we can mimic a process, and we can mimic an ecosystem ("like having a city that functions as well as a forest," says Benyus).
With wind power, there are opportunities across that spectrum, and they are helping to address some of the biggest problems in the field: turbine efficiencies and space requirements.
The efficiency of wind turbines suffers largely because of the variability of wind speeds. At higher speeds, most new turbines function well, but just as an airplane loses lift as its air speed drops past a certain point, turbine blades stall when the wind speed drops. In order to handle a variety of wind speeds without stalling, most turbine blades are positioned well below the ideal angle for generating power. If there was a way to tilt those blades so that more of the wind’s energy could be captured—in effect, increasing the angle of attack of the wind on the blade—the output of the turbine could be increased.
Enter humpback whales. These massive mammals have small bumps known as tubercles along the leading edge of their fins. According to West Chester University biology professor Frank Fish, adding those tubercles to the edge of a turbine blade can provide the needed improvement in the angle of attack by delaying stall, and they do it without causing a severe increase in drag. For whales, this means improved efficiency in swimming; for wind turbines, it means more power. And this isn’t just theoretical: Fish helped start a company called WhalePower that is marketing the technology.
"You can modulate the pitch of your windmill so that it operates at higher angles of attack without fear of stalling," Fish says. In other words, by tilting the blades farther in relation to the wind angle, turbines can generate more power without the usual risk of a stalled blade causing an asymmetry and the turbine "shaking itself to death." As an added bonus, the tubercle turbines could potentially reduce a noise problem known as tip chatter, in which stalling at the blade’s tip causes a vibration.
What’s more, the tubercled turbine is more efficient. Using a 35-kilowatt test windmill (large, utility-scale wind turbines have a generating capacity of around 5 megawatts), researchers found that adding tubercles to standard turbine blades bumped up the efficiency by 20 percent. That is, the same amount of wind produced 20 percent more electricity on a windmill with tubercles than without.
So far, WhalePower is selling tubercle technology for industrial ventilation fans but not yet for mass-produced wind turbines.
Nature’s designs are also applicable further up Benyus’s three-level biomimicry scale. Somewhere between the function and ecosystem level lies an ongoing project led by John Dabiri, a professor of aeronautics and bioengineering at Caltech. Dabiri wondered if there could be a way to improve the spacing requirements of wind turbines, so he started looking at fish.