Published on September 5th, 2012 | by Joshua S Hill4
Improving the Efficiency at the Heart of the Wind Farm
A wind farm is subject to many influences, but maybe it’s biggest challenge is itself. When the wind hits that first turbine, all is well, but the wind coming out the other side of said turbine is a mess of whorls, large and small, which flow on to the next turbine in the row and the next and…. In fact, the turbines in the subsequent rows deliver up to 40 percent less power than those in the first.
Two recently published articles in the journal Boundary-Layer Meteorology look at the problems wind farms cause for themselves, and how it could be possible to rectify the issues.
Study #1, Trying a New Layout
The first study was co-written by Yu-Ting Wu, a PhD student at EPFL’s Wind Engineering and Renewable Energy Laboratory (WIRE), and Fernando Porté-Agel, also at WIRE.
“One important factor for designing a wind farm is its layout, or how the turbines are positioned relative to each other,” says Yu-Ting Wu.
Wu compared the results from a numerical simulation of the wind through a wind farm to wind tunnel experiments, focusing specifically on where the wind turbines were placed within the wind farm. He found that simply changing the wind farm from a square grid can increase the total efficiency of the wind farm, giving the wind more time to recover after it has passed through the first wind turbine.
Finding the perfect setup, however, is a lot of trouble.
“You have to remember that layout is relative, and changes with the wind direction,” says Wu.
If the wind is blowing from the south, two turbines may be one behind the other. If it comes in from the east, they’re all of a sudden right beside one another.
Study #2, Warmer is Better
The second article, involving Porté-Agel and colleagues from the University of Minnesota, looked at the role atmospheric stability plays on a wind farm’s power output. For their experiments, the researchers turned on the floor heating in their wind tunnel to study the effects of convection on the wake behind a turbine.
They found that despite the increased turbulence that occurs on hot days, the flow behind the wind turbine actually recovers faster than in less turbulent nocturnal winds.
This means that on hot days the second row of turbines would not lose as much efficiency as they might during the night. According to the authors, the stronger turbulence surrounding the turbine wake draws in more forward momentum, which leads to faster recovery of the flow.