Less is more for cost-efficient wind farms
A wind tunnel on the Homewood campus the researchers used to experiment with variables such as the correct spacing of wind turbines (Image: Will Kirk/Homewoodphoto.jhu.edu)
While there are increasing numbers of large wind farms being built around the world, many of these projects are underperforming and not producing as much power as expected. New research suggests the reason could be that the wind turbines are being placed too close together. The researchers say that spreading the turbines out will result in a more cost-efficient wind farms and they’ve come up with a formula through which the optimal spacing for a large array of turbines can be obtained.
The newest wind farms, be they on or offshore, typically use turbines with rotor diameters of around 300 feet (91 m), which are typically spaced about seven rotor diameters apart. Charles Meneveau, a fluid mechanics and turbulence expert at Johns Hopkins University, working with Johan Meyers, an assistant professor at Katholieke Universiteit Leuven in Belgium, conducted research that indicates placing the wind turbines more than twice as far apart as current layouts – 15 rotor diameters apart – results in more cost-efficient power generation.
Meneveau says that earlier computational models for large wind farms – those consisting of hundreds or even thousands of turbines – were based on simply adding up what happens in the wakes of single wind turbines. However, his new spacing model takes into account the interaction of arrays of turbines with the entire atmospheric wind flow.
The researchers claim that the energy generated in a large wind farm has less to do with horizontal winds and is more dependent on the strong winds that the turbulence created by the tall turbines pulls down from higher up in the atmosphere. Using high-performance computer simulations and wind tunnel experiments, they determined that in the correct spacing, the turbines alter the landscape in a way that creates turbulence, which stirs up the air and helps draw more powerful kinetic energy from higher altitudes.
The study by Meneveau and Meyers was presented recently at a meeting of the American Physical Society Division of Fluid Dynamics. However, Meneveau says further research is needed to learn how varying temperatures can affect the generation of power on large turbines. He has applied for continued funding to conduct such studies.
About the Author
Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.
All articles by Darren Quick
This is TOTAL nonsense!
The problem is the fan design itself.
And it was solved long ago by the Engineer William Allison.
Seeing the 2 bladed fan would have driven him quickly into hysterics.
The answer is a 10 bladed fan in a 12 blade configuration.
If that wind tunnel does not allow for free air flow then their results are erroneous because they have a supercharged test facility. Completely false for testing the free flow of air in the atmosphere.
See the article in altenergy.mag on Bill Allison and his 59% efficiency fans.
That the American Engineering community cannot pull itself together to set up a proper testing facility and test all comers for efficiency is actually shameful.
\" correct spacing, the turbines alter the landscape in a way that creates turbulence, which stirs up the air and helps draw more powerful kinetic energy from higher altitudes\"
I always thought that the power was more from horizontal winds than vertical but my conception was for single turbines. As turbines remove energy from the wind and decrease wind velocity, they may produce a vacuum effect with respect to the air mass above it. Simply put, the air flowing just above the turbine blades and not only to the back of the blades would affect the air flow going to the other turbines in the area. Correct spacing is important for efficiency.
I like the bit at the end:\'He has applied for continued funding to conduct such studies.\' That says it all, really.
Why don\'t they erect one windmill, and then test its efficiency? Then put another one up at what they think is a good distance, and test that? And so on. Seemple!
Using what is obviously an \'Off-the-shelf\' model aircraft propeller - which is designed to be driven by a shaft - as a means of extracting wind energy is ludicrous. If that is indeed what those at the Homewood Campus are doing, per their photo.
Surely, the most efficient designs for extracting energy from the wind will be more along the lines of drum-type, multi-bladed, spiral-chord vane assemblies - which may be mounted anywhere - and particularly in the turbulent air around building tops - either vertically or horizontally. Perhaps a drum-type structure, incorporating a spiral version of William Allison\'s blade design may prove the most practical.
Food for thought ...
Not all oversights should be viewed as mistakes however, the mistake would be not to find an application for the result, ie I am sure there are more than one or two windswept areas that may benefit electrically and climatically from closely spaced turbines.
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