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Wind turbine placement to optimize wind power generation for a given area


22:03 July 13, 2011

The Caltech Field Laboratory for Optimized Wind Energy where arrays of closely spaced vert...

The Caltech Field Laboratory for Optimized Wind Energy where arrays of closely spaced vertical-axis wind turbines were tested

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Although wind power energy production in 2010 was estimated to be only about 2.5 percent of worldwide electricity usage, wind turbines are considered a mature technology with many experts suggesting that we're approaching the theoretical limit of individual wind turbine efficiency. For this reason, researchers are now looking at new approaches to wind farm design to increase the power output of wind farms. Researchers at the California Institute of Technology (Caltech) have been conducting a field study and claim the power output of wind farms can be increased at least tenfold by optimizing the placement of turbines on a given plot of land.

While most wind farms employing horizontal-axis wind turbines (HAWTs) - the standard propeller-like turbines most commonly found in wind farms around the world - space the individual turbines around seven rotor diameters apart, a recent study found that spacing of at least 15 rotor diameters apart produced the most cost-efficient power generation. But even though spreading the turbines out increases the cost-efficiencies by allowing for fewer individual turbines, it also lowers the power output of a given plot of land.

To compensate for the energy loss resulting from the wake generated from one turbine interfering with neighboring turbines, HAWT wind farms also resort to using bigger blades and taller towers that are capable of taking advantage of the more powerful gusts of wind found at greater heights. But these larger structures result in increased production and maintenance costs, visual, acoustic, and radar signatures problems, as well as more bat and bird impacts.

In an attempt to develop a more efficient wind farm design that maximizes its energy-collecting efficiency at heights closer to the ground, John Dabiri, Caltech professor of aeronautics and bioengineering, and his colleagues turned to vertical-axis wind turbines (VAWTs) - turbines like the Windspire that have vertical rotors and look like eggbeaters sticking out of the ground. VAWTs aren't more prominently used today because they tend to be less efficient individually and previous generations suffered from structural failures relating to fatigue.

But Dabiri says, "advances in materials and in predicting aerodynamic loads have led to new designs that are better equipped to withstand fatigue loads." Additionally, because VAWTs can be positioned very close together they are able to capture nearly all the energy of the blowing wind, and so the lower efficiency of individual turbines is not as much of an issue.

Dabiri carried out field tests in the summer of 2010 at an experimental farm known as the Field Laboratory for Optimized Wind Energy (FLOWE), which houses 24 10-meter-tall, 1.2-meter-wide VAWTs. In the field tests, which used six VAWTs, Dabiri and his colleagues measured the rotational speed and power generated by each of the turbines when placed in a number of different configurations. One turbine was kept in a fixed position for every configuration, while the others were on portable footings that allowed them to be shifted around.

They found that the aerodynamic interference between neighboring turbines was completely eliminated when all the turbines in an array were spaced four turbine diameters (roughly five meters or 16 feet) apart. In comparison, propeller-style HAWTs would need to be spaced 20 rotor diameters apart - which equates to a distance of more than one mile for the largest wind turbines currently in use - for the aerodynamic interference to be eliminated.

The six VAWTs generated from 21 to 47 watts of power per square meter of land area, while a comparably sized HAWT farm generates just two to three watts per square meter.

"Our results are a compelling call for further research on alternatives to the wind energy status quo," Dabiri says. "Since the basic unit of power generation in this approach is smaller, the scaling of the physical forces involved predicts that turbines in our wind farms can be built using less expensive materials, manufacturing processes, and maintenance than is possible with current wind turbines."

The researchers plan to scale up their field demonstration and are looking to improve upon the off-the-shelf wind turbine designs used for their field study.

The findings of the field study conducted by Dabiri and his Caltech colleagues appear in the July issue of the Journal of Renewable and Sustainable Energy.

User Comments (12)

Sorry Gizmag but you're guilty of fuelling the bird/bat wind turbine death myth.

How Stuff Works:

"Collisions with wind turbines account for about one-tenth of a percent (0.1%) of all "unnatural" bird deaths in the United States each year. "


comment Ben Crow - July 14, 2011 @ 07:15 am PDT

The question is: What is the cost difference between a large HAWT and the equivalent number of smaller VAWTs (to produce the same power output) The space required for VAWTs is much less, as is the environmental impact. VAWTs can also be installed on buildings much more acceptably. There are actually horizontal versions(if that is not a contradiction of terms).

It would be good to compare the two different types (HAWT & VAWT) in the same location.

comment windykites1 - July 14, 2011 @ 07:49 am PDT

That's a nice piece of research. I wonder, though, how well it scales to larger numbers of units. Surely in a large close-spaced array the ones in the middle won't be getting as much wind.

comment David Evans - July 14, 2011 @ 08:50 am PDT

World war 4 will be faught with sticks and Rocks Over the Placement of wind turbines . Have You heard the Phrase.... He stole the wind from my sails ?

comment Mark Burnett - July 14, 2011 @ 09:23 am PDT

Here we go again...

The current fashion of using the 1944 incompetent and very inefficient design of NASA is being called mature?

Anything but.

And this design is using less efficient configuration as reported here?

Less efficiency of low efficiency? How soon does it get to 0 efficiency like what happened in Canada causing a political revolution. They had 0 efficiency for 6 months due to icing.

Don't you think that it's time for certifying bodies to demand manufacturers to post efficiencies? Talking efficiencies here is talking nonsense. We need figures.

There needs to be a standard testing facility to determine efficiencies rather that forcing us to witness all these cackamamie designs ullustrating how deficient this generation is.

Don't forget, the honeywells can be stacked vertically and they are way more efficient.


comment Island Architect - July 14, 2011 @ 09:58 am PDT

How about giving up on wind already please.

Billions out of your pocket has already been spent to verify that, yes, just because it is greenwashed does not mean that it generates electricity you need.

Those of us over thirty knew this already but everybody needs to learn by experience.

comment Todd Dunning - July 14, 2011 @ 12:32 pm PDT

Oh, give it a rest, Todd. The world is not going to build thousands of new nuclear reactors just because you like them. Most people "over thirty" are smarter than that.

comment Gadgeteer - July 14, 2011 @ 02:41 pm PDT

Oh Todd, go back to faux news, so sad such ignorance in the year 2011 still exists, I call them flatlanders, bet he goes to church every Sunday and is a devout conservative too and man is not making the earth warmer right Todd? yep I am over thirty too

comment Bill Bennett - July 14, 2011 @ 07:51 pm PDT

The other thing to look at in terms of land usage efficiency is what can be done with te land in between the devices. HAWTs allow for normal agriculture which is probably not as easy using the higher density VAWTs.

Todd, are you really that short-sighted? Do the terms "closed loop" or "full circle" mean anything to you? Have you managed to come up with a way to make nuclear completely failsafe and a way to process nuclear waste in to a non-toxic form (not just seal it in a container and store it in a third world country)?

comment Bernhard - July 15, 2011 @ 03:20 am PDT

Creating electricity with wind is certainly a "neat" pastime... large dollars in research keeps a bunch of people busy... and the constant discovery is that wind generation continues to be inefficient... and... produces a miniscule smattering of electricity... whereas... hydro power has been around for over a hundred years... is renewable... produces a larger share of electricity... but receives very little funding for research...

When do we seriously entertain the idea of applying a fair share of our funding toward hydro research? As soon as the novelty of wind power weras off?? I'm just saying.....

comment Uncle Pete - July 15, 2011 @ 06:05 am PDT

Wind generated power is already cheaper than nuclear power to produce and with none of the catastrophic downsides. It can also easy to put the power where it is going to be consumed without the creation of a new transmission grid.

Anyone that says hydroelectric is renewable is pretty clueless about what happens during times of drought or when the dam is filled with mud after 30 years. Dams also destroy fisheries and cause economic loss to numerous communities that are downstream while providing heavily federally subsidized water and power to a few communities and corporate farmers. Thankfully dams are starting to be dismantled.

Coal gets a 500 billion dollar subsidy in not having to comply with safety or environmental regulations and the amount of damage done to entire watersheds and to peoples health from the lead, mercury, and particulate pollution the plants create.

No nuclear power plant would exist without a 100% exemption from any liability provided by the federal government and even then the industry gets billions of dollars in subsidies and special rates.

IN countries like Germany and even China where corporate interests do not rule the country they are moving away from nuclear power and toward solar and wind generated power. Only in the USA do we have a government that continues to support dead and dying industries and ignores the damage done to the people and the economy.

comment Calson - July 15, 2011 @ 01:56 pm PDT

Calson: I agree with everything except the last sentence. Anywhere gov subsidizes anything BAD results occur, which is everywhere gov has the resources. In a third world country free enterprise might exist and solve problems until the gov wakes up and moves it to demand a cut. That's the beginning of the end.

Energy guru Amory Lovins has stated that there would be no energy crisis without subsidies.

The grid serves big business/gov. Whenever we can replace it with distributed production we will prosper for a while until gov finds a way to tax it. The fundamental obstacle to life is gov.

comment voluntaryist - August 1, 2011 @ 11:43 pm PDT
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