Friday, August 31, 2018

What Wind Farms Can Learn from Football Teams

Winning football teams are composed of members that work well together, capitalizing on each other’s strengths and compensating for each other’s weaknesses. But that mindset can be applied in a lot of different circumstances—it turns out that wind farms can benefit from this strategy, too. New research shows that by incorporating cooperation, wind farms could output as much as ten times more power per area than they do now...and that would be a win for all of us. The research will be published in an upcoming issue of the American Physical Society’s journal Physical Review Fluids.

A wind farm in Turlock, California.
Image Credit: Photo by American Public Power Association on Unsplash.
“Most existing wind energy research focuses on improving the performance of individual turbines,” says Paolo Luzzatto-Fegiz of the University of California, Santa Barbara. The thing is, most wind turbines don’t operate in isolation. Most turbines are just one point in an array of hundreds or even thousands of turbines that compose a wind farm. This left him wondering, could wind farms perform even better if turbines were optimized for cooperation, rather than individual success?

If you’ve driven past a wind farm, you may have noticed that there’s a lot of empty space. That’s because each turbine casts a wind shadow. As its blades spin, taking energy out of the wind, the air surrounding a turbine slows down. If you put another turbine in that slow-moving air, it will produce significantly less power than if were farther away. Wind shadows can reduce a wind farm’s power output by as much as 40 percent, so farms leave extra space between turbines.

But a spinning turbine doesn’t just slow down air, it creates turbulence that ripples through the space around nearby turbines, interacting and changing the flow of the air all down the line. In fact, the flow is fundamentally different in large wind farms than in a single turbine system, say the researchers, and so is the physics. Existing theoretical models don’t take this fully into account.

To create a more accurate picture, Luzzatto-Fegiz and the University of Cambridge’s Colm-cille Caulfield built a model of wind farms as interconnected systems, rather than a sum of individual parts. This required considering the wind in three different layers:

• the bottom layer that contains the turbines;

• the middle layer, a turbulent boundary layer that is influenced by the properties of the wind farm; and

• the upper layer, far above the wind farm, where the properties depend only on the conditions of the atmosphere.

Luzzatto-Fegiz had been thinking about this idea for several years, but wasn’t quite sure how to model the bottom layer in a way that wasn’t based on any one turbine design or arrangement—he wanted the model to be as general as possible. Inspiration struck on a walk with his then-one-year-old son. “While looking at a grove where the trees were made to oscillate by the wind, it occurred to me that the wind through an array of wind turbines could be modeled mathematically like wind through a tree grove,” he recalls.

A wind farm in Seville, Spain.
Image Credit:Photo by Johanna Montoya on Unsplash.
The next challenge was modeling the turbulent layer above the wind farm, the middle layer in which the turbine array pulls energy from the atmosphere. This time when inspiration struck, he was standing in a doorway. “[I was] talking with my then-officemate, Julien Landel, about oceanic flows, when it occurred to me that the region of vigorous, turbulent mixing above a wind farm could be modeled using the same mathematical tools that oceanographers use for plumes or hydrothermal vents,” recounts Luzzatto-Fegiz.

Putting all of this together, the researchers built a model that describes the essential features of a large wind farm regardless of the turbine design or the layout. They tested the models against field data from different wind farms and experiments, and the model did great.

Then, based on their model, the researchers found expressions for how much power per area an ideal wind farm can generate. In other words, they showed what’s possible in a farm whose turbines cooperate as a perfect team. This means that, for the first time, people have a standard against which they can compare a wind farm’s power output. And it shows that current farms have a lot of room for improvement—they could be doing up to ten times better.

This work doesn’t recommend any specific new designs for turbines or wind farms—that’s beyond its scope—but it shows that designers need to consider cooperation if they really want to increase the power output of wind farms. Turbines designed with cooperation in mind would probably not perform as well on their own, Luzzatto-Fegiz says, “but they could lead to arrays that significantly outperform existing ones.”

It’s a lesson that most coaches already know: Teams who cooperate have a distinct advantage over a group of talented but self-focused individuals pointed in the same direction. In the case of wind energy though, we’re all cheering for the same team.

—Kendra Redmond

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