A subtle tweak could make wind farms more efficient
How turbines can share the wind
A wind farm in Alberta took a gamble last year. A group of engineers at Stanford University asked wind operator TransAlta to let them modify a few of their multi-million-dollar turbines for a couple days. In return, the Stanford team said the turbines could generate more power with greater consistency. The company agreed to the test.
The researchers wanted to turn the rotors — the piece of a turbine blades are attached to — away from the wind at certain times. The idea sounds counter-intuitive, since individual turbines would perform worse while the group was supposed to generate more power collectively. But the scheme worked — more or less.
When wind blows over a wind farm, upwind turbines hog the breeze, creating a pocket of slow, choppy air for downwind turbines to contend with.
“That makes it more difficult for the downwind turbines to do their job,” said Dr. John Dabiri, an engineer at Stanford University who specializes in wind energy efficiency. The disturbance is called a wake, like the turbulent water that forms behind a rock in a streaming river, and it can decrease energy production by 10 percent onshore and upwards of 20 percent at offshore wind farms.
That lost energy adds up. With the need to ramp up wind energy and other renewables dramatically over the coming years, Dabiri has been trying to figure out how to make the existing wind capacity more efficient.
He’d run computer models of what’s called “wake steering,” turning the blades slightly away from the wind so downwind turbines get a greater share of wind, but he hadn’t convinced a wind farm to test the idea out until the TransAlta experiment.
“We are really fortunate to find a forward-thinking company,” Dabiri said. “Otherwise, all these ideas, they just end up sitting on the shelf in academic labs.”
By employing wake steering, Dabiri’s team decreased the variability of the power generation by more than 70 percent over ten days of testing at TransAlta’s site in the yellow, rolling fields just east of the Rockies. The full results were published in July in the Proceedings of the National Academy of Sciences.
Under average wind speeds, wake steering increased power production at the wind farm by nearly 10 percent when the wind blew from the northwest, an unusual direction for the farm. But overall energy production increased by only 0.3 percent over the full trial. Despite the modest energy gain, Dabiri wasn’t disappointed. The test proved wake steering works in the real world and could be deployed on a wide scale.
“That first demonstration is hopefully going to give some courage to some of the other companies,” Dabiri said.