Wind-turbine placement produces tenfold power increase, researchers say

Jul 13, 2011 by Kathy Svitil

(PhysOrg.com) -- The power output of wind farms can be increased by an order of magnitude -- at least tenfold -- simply by optimizing the placement of turbines on a given plot of land, say researchers at the California Institute of Technology (Caltech) who have been conducting a unique field study at an experimental two-acre wind farm in northern Los Angeles County.

A paper describing the findings -- the results of field tests conducted by John Dabiri, Caltech professor of aeronautics and bioengineering, and colleagues during the summer of 2010 -- appears in the July issue of the Journal of Renewable and .

Dabiri's experimental farm, known as the Field Laboratory for Optimized (FLOWE), houses 24 10-meter-tall, 1.2-meter-wide vertical-axis wind turbines (VAWTs)—turbines that have vertical rotors and look like eggbeaters sticking out of the ground. Half a dozen turbines were used in the 2010 field tests.

This video is not supported by your browser at this time.

Despite improvements in the design of wind turbines that have increased their efficiency, are rather inefficient, Dabiri notes. Modern farms generally employ horizontal-axis wind turbines (HAWTs)—the standard propeller-like monoliths that you might see slowly turning, all in the same direction, in the hills of Tehachapi Pass, north of Los Angeles.

In such farms, the individual turbines have to be spaced far apart—not just far enough that their giant blades don’t touch. With this type of design, the wake generated by one turbine can interfere aerodynamically with neighboring turbines, with the result that "much of the wind energy that enters a wind farm is never tapped," says Dabiri. He compares modern farms to "sloppy eaters," wasting not just real estate (and thus lowering the power output of a given plot of land) but much of the energy resources they have available to them.

Designers compensate for the energy loss by making bigger blades and taller towers, to suck up more of the available wind and at heights where gusts are more powerful. "But this brings other challenges," Dabiri says, such as higher costs, more complex engineering problems, a larger environmental impact. Bigger, taller turbines, after all, mean more noise, more danger to birds and bats, and—for those who don’t find the spinning spires visually appealing—an even larger eyesore.

The solution, says Dabiri, is to focus instead on the design of the wind farm itself, to maximize its energy-collecting efficiency at heights closer to the ground. While winds blow far less energetically at, say, 30 feet off the ground than at 100 feet, "the global wind power available 30 feet off the ground is greater than the world’s electricity usage, several times over," he says. That means that enough energy can be obtained with smaller, cheaper, less environmentally intrusive turbines—as long as they're the right turbines, arranged in the right way.

VAWTs are ideal, Dabiri says, because they can be positioned very close to one another. This lets them capture nearly all of the energy of the blowing wind and even wind energy above the farm. Having every turbine turn in the opposite direction of its neighbors, the researchers found, also increases their efficiency, perhaps because the opposing spins decrease the drag on each turbine, allowing it to spin faster (Dabiri got the idea for using this type of constructive interference from his studies of schooling fish).

In the summer 2010 field tests, Dabiri and his colleagues measured the rotational speed and power generated by each of the six turbines when placed in a number of different configurations. One turbine was kept in a fixed position for every configuration; the others were on portable footings that allowed them to be shifted around.

The tests showed that an arrangement in which all of the turbines in an array were spaced four turbine diameters apart (roughly 5 meters, or approximately 16 feet) completely eliminated the aerodynamic interference between neighboring turbines. By comparison, removing the aerodynamic interference between propeller-style wind turbines would require spacing them about 20 diameters apart, which means a distance of more than one mile between the largest now in use.

The six VAWTs generated from 21 to 47 watts of power per square meter of land area; a comparably sized HAWT farm generates just 2 to 3 watts per square meter.

"Dabiri's bioinspired engineering research is challenging the status quo in wind-energy technology," says Ares Rosakis, chair of Caltech's Division of Engineering and Applied Science and the Theodore von Kármán Professor of and professor of mechanical engineering. "This exemplifies how Caltech engineers' innovative approaches are tackling our society's greatest problems."

"We're on the right track, but this is by no means 'mission accomplished,'" Dabiri says. "The next steps are to scale up the field demonstration and to improve upon the off-the-shelf wind-turbine designs used for the pilot study." Still, he says, "I think these results are a compelling call for further research on alternatives to the wind-energy status quo."

Explore further: Self-cooling solar cells boost power, last longer

More information: This summer, Dabiri and colleagues are studying a larger array of 18 VAWTs to follow up last year's field study. Video and images of the field site can be found at dabiri.caltech.edu/research/wind-energy.html

Related Stories

Smart wind turbines can predict the wind

Jan 05, 2010

Risø DTU researchers have recently completed the world’s first successful test on a wind turbine with a laser-based anemometer built into the spinner in order to increase electricity generation.

Optimizing large wind farms

Nov 23, 2010

Wind farms around the world are large and getting larger. Arranging thousands of wind turbines across many miles of land requires new tools that can balance cost and efficiency to provide the most energy for ...

Recycling wind turbines

Sep 21, 2007

The development of wind power promises much in terms of providing us with renewable energy for the future and wind turbines could be the most effective way to harness that power. Danish researchers now suggest that in order ...

Germany's first offshore wind farm begins turning

Apr 27, 2010

The blades began turning at Germany's first offshore wind farm Tuesday, 45 kilometres (28 miles) off the coast in the North Sea, with 12 turbines producing energy for 50,000 households.

Recommended for you

User comments : 12

Adjust slider to filter visible comments by rank

Display comments: newest first

antialias_physorg
5 / 5 (4) Jul 13, 2011
This is a rather important finding. I'm curious why this effect wasn't investigated/discovered earlier.
After all: Simulations for modern wind parks must have been run beforehand.
SiBorg
3 / 5 (3) Jul 13, 2011
Simulations of energy yield are run from a very early stage in a project right up to the point where construction is ready to begin.

The suggestion that layouts are not optimised to minimise wake losses and maximise available land usage is completely daft. Financial backing for a project would be very hard to come by without evidence of an optimised layout.

There are definite appeals to a VAWT type but to think that there aren't engineering difficulties with them is a bit facile. Having a rotating shaft the height of the turbine is not simple if you want utility scale generation, nor is the materials science involved in making strong light blades.

The idea of constructive interference between turbines is pretty interesting.
Eikka
not rated yet Jul 13, 2011
Isn't the problem of VAWTs that they operate well on low speeds, but once the wind picks up they get "saturated" and won't produce any more power, whereas HAWTs can increase production all the way up to gale force winds.

So they are kinda wasteful as well, but in another way. On low wind speeds they generate more, but on high wind speeds they generate much less, which is a problem because wind power increases in the cube of wind speed. That puts the VAWT at a significant disadvantage when scaling things up.

Statistically speaking, the wind speed range where VAWTs work the best contains the least amount of the available energy. The main advantage comes if you need small amounts of power very steadily, because low wind speeds happen more often.
yoatmon
not rated yet Jul 13, 2011
I think someone has bats in his belfry. Bats are capable of pin-pointing tiny insects in full flight but are incapable of sourcing the blades of a wind turbine??
yoatmon
not rated yet Jul 13, 2011
Disadvantages of vertical axis wind turbines (VAWTs):
http://en.wikiped..._turbine
Some disadvantages that the VAWTs possess are that they have a tendency to stall under gusty winds. VAWTs have very low starting torque, as well as dynamic stability problems. The VAWTs are sensitive to off-design conditions and have a low installation height limiting to operation to lower wind speed environments.

The blades of a VAWT are prone to fatigue as the blade spins around the central axis. The vertically oriented blades used in early models twisted and bent as they rotated in the wind. This caused the blades to flex and crack. Over time the blades broke apart and sometimes leading to catastrophic failure. Because of these problem, Vertical axis wind turbines have proven less reliable than horizontal-axis wind turbines (HAWTs).
javjav
4 / 5 (1) Jul 13, 2011
Why not use both? Put HAWT at 30feet and VAWT at 120m. plus solar thermal panels on the floor. It would maximize watts per square meter, and also the usage of costly infrastructures like electrical grid usage, maintenance resources.etc. Solar thermal panels could be optimal because they could share the same turbines (wind steam), thus producing more constant juice. Blades and tubes could be made transparent to avoid shadows. And the solar panels can be placed strategically to create a temperature gradient producing some extra wind. Finally, these panels could be shaped to funnel wind to nearby turbines.
david_42
4.5 / 5 (2) Jul 13, 2011
yoatmon - old designs certainly had these problems. Some of them had such low starting torque that they had to be spun-up electrically to get going. New designs with helical blades overcome that problem as well as the flexing problems. Stalling in gusts or high winds protects a turbine from over-reving. Finally, designs that can operate at lower wind speeds will produce power more of the time, in more locations and often outperform high velocity turbines that stand idle much of the time. Most vertical axis turbines are lucky to produce power 25% of the time, even in the best locations.

Slow and steady just might be the best route.
boB_K7IQ
not rated yet Jul 14, 2011
Those are Windspire VAWTs. Why is it that they had to use an animated simulation for their video ? Couldn't they have just taken a real video with real turbines in the wind ? Unfortunately this is typical of VAWT windmill promos. VAWTs are less efficient than HAWTs but maybe there is hope for these particular ones if they can make them hold together which I understand they are having some success with.
boB
Husky
not rated yet Jul 14, 2011
i am with javjav on this, mixing high horizontal and low vertical turbines, that does'nt seem to bite eachother very much, also i would like to know if its possible to do away with the vertical towers and driveshafts of VAWT by suspending them as series of vertical blades between wires and just anchortowers at the end of the wire, the wires would act as a drivebelt so thats multiple small VAWTs would drive one big generator and hence advantage could be taken of scale leverage while saving on construction material, in fact the metal towers of the higher horizontal turbiones that are mixed in could serve as the anchorpoints for the VAWTS wires
antialias_physorg
not rated yet Jul 14, 2011
i am with javjav on this, mixing high horizontal and low vertical turbines, that does'nt seem to bite eachother very much,


Draw it on a piece of paper. You'll see that it bites itself - either because of statics of because of collision. The only way this would work is you make the rotors of the HAWT part so small that they become ineffective.
tarheelchief
not rated yet Jul 18, 2011
Each innovator can point to weaknesses in his rivals.The solar power group has to contend with the efficiency of the panels.The wind powered group must contend with the birds and erratic nature of the source.Tidal power has serious problems with corrosion and biological issues.What is needed is a truce in the marketplace and placements of various sources around a state or region.The present grid can be utilized most effectively if the sources also have storage units for the energy.
antialias_physorg
not rated yet Jul 19, 2011
Tidal power has serious problems with corrosion and biological issues.

Personally I like the limpet design which suffers from neither.
http://www.darvil...wave.htm
The test powerplant has been operating for over 10 years now.
http://www.hi-ene...g-EN.htm