Wind jet: A rendering of a new turbine design, which can increase the energy captured from wind.
FloDesign Wind Turbine
A design that draws on jet engine technology could halve the cost of generating electricity from wind.
FloDesign Wind Turbine, a spin-off from the aerospace company FloDesign based in Wilbraham, MA, has developed a wind turbine that could generate electricity at half the cost of conventional turbines. The company recently raised $6 million in its first round of venture financing and has announced partnerships with wind-farm developers.
The company's design, which draws on technology developed for jet engines, circumvents a fundamental limit to conventional wind turbines. Typically, as wind approaches a turbine, almost half of the air is forced around the blades rather than through them, and the energy in that deflected wind is lost. At best, traditional wind turbines capture only 59.3 percent of the energy in wind, a value called the Betz limit.
FloDesign surrounds its wind-turbine blades with a shroud that directs air through the blades and speeds it up, which increases power production. The new design generates as much power as a conventional wind turbine with blades twice as big in diameter. The smaller blade size and other factors allow the new turbines to be packed closer together than conventional turbines, increasing the amount of power that can be generated per acre of land.
The idea of enshrouding wind-turbine blades isn't new. But earlier designs were too big to be practical, or they didn't perform well, in part because the blades had to be very closely aligned to the direction of the wind--within three or four degrees, says Stanley Kowalski, FloDesign's CEO. The new blades are smaller and can work at angles of up to 15 to 20 degrees away from the direction of the wind.
From the front, the wind turbine looks something like the air intake of a jet engine. As air approaches, it first encounters a set of fixed blades, called the stator, which redirect it onto a set of movable blades--the rotor. The air turns the rotor and emerges on the other side, moving more slowly now than the air flowing outside the turbine. The shroud is shaped so that it guides this relatively fast-moving outside air into the area just behind the rotors. The fast-moving air speeds up the slow-moving air, creating an area of low pressure behind the turbine blades that sucks more air through them.
It's plausible that such a design could double or triple a turbine's power output, says Paul Sclavounos, a professor of mechanical engineering at MIT. Part of the increase comes simply from guiding the air to the turbine with the shroud. But Sclavounos notes that it also helps to use the wind surrounding the turbine to speed up the airflow, because the power produced by a wind turbine increases with the cube of the wind speed. The key question is whether the new turbines can be built and maintained at a low-enough cost, Sclavounos says.
FloDesign has already built a small prototype for wind-tunnel tests. Its next step is to build a 12-foot diameter, 10-kilowatt system for field tests. The prototype will be finished by the end of next year or early in 2010, with commercial wind turbines to follow. (The company is not yet taking orders.) Eventually the company plans to make turbines as large as one megawatt.
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Synergy with Wind Prediction Techniques
Given its sensitivity to wind direction, there should be further gains from this new design with an improved an ability to predict the wind direction and velocity a la your Nov. 6th article, "Laser Sensors for Wind Turbines"
http://www.technologyreview.com/energy/21643/?a=f
Guest (Peter Williams)
I'm guessing that this new design will have another benefit. Unlike a conventional wind turbine it would appear more likely to be viewed as a solid object by birds, so they don't fly into the blades and get chopped up. This is a big issue, for example, with the Altamont Pass windfarm in CA, which is on the Pacific Flyway - as a result, they regularly find diced eagle and such on the ground, which is to put it mildly an ecological drawback...
Have you ever seen a sliced up dead bird below a wind turbine? I have worked around wind turbine for 5 years and have never seen one. Wind turbines being responsible for slicing up birds in flight is an urban myth that sounds plausible, but in reality is not true.
Wind turbines, depending on the wind speed, turn relatively slow (~20 rpm), much too slow to swat an unsuspecting bird. The blades are large (i.e. scary), move slow, and the system’s generator and gear box makes enough noise to warn or deter most birds or flying creatures from approaching the wind turbine when it active. Its possible that a bird could be struck by a moving wind turbine, but it is the rare exception not the rule.
When you drive through northern Germany, and Holland you can see 100s of wind turbine systems actively working, large ones, small ones, some with one, two, and three blades, all installed in the last 15-20 years. Have you heard of Germany or Holland’s Environmentally active Green Party leaders complain of a demising bird population? My guess is that more birds die from flying into windows than by striking or being stuck by a wind turbine.
I can't believe that the editors an a technology publication affiliated with MIT would let this piece of gargage get past them! It reflects a total ignorance of basic physics -- say the conservation of energy, for starters.
Any wind turbine device (regardless of design) produces power by extracting kinetic energy from the stream of passing air that it is able to act upon. "Extracting kinetic energy" means "slowing it down". You absolutely cannot avoid slowing the air flow, as the video and article suggest, and still generate any power.
When the speed of an air flow is reduced, the flow necessarily broadens and forces a portion of the upstream flow to divert around it. The Betz limit is what you get when you optimize the tradeoff between the fraction of the kinetic energy extracted from each ton of air passing through the turbine's area of influence and the total flow through that area. It's a fundamental limit, and can't be circumvented by clever design.
There's some wiggle room in determining just what the turbine's "area of influence" actually is. For a conventional wind turbine, it's the area swept out by the rotating blades. For a shrouded device like this one it's .. something different, and very hard to calculate. But the shroud can indeed act to enlarge the turbine's "area of influence", and accelerate the air flow through the turbine itself.
As somebody noted above, it's been tried before. Didn't work out too well, as the shroud was heavier and less effective at increasing output from the ducted fan than simply making the blades longer.
This design does have a novel feature that I don't think anyone has tried before, and that's the scalloped trailing edge on the shroud. It's just possible that the turbulent flow induced by those scallops does actually work to enlarge the turbine's "area of influence" more effectively than a smooth shroud.
If that is the case, you'd never know it from the article and video. And it's inconsistent with the other big claim that is made, which is that these devices don't need to be spread out the way conventional conventional wind turbines must be. Any wind device that can extract as much power from the wind as a conventional turbine will end up needing to be just as widely spaced from its neighbors as the conventional wind turbine. That too is a fundamental consequence of fluid dynamics that can't be circumvented.
The bulk of your response is correct for free stream flow but this design is based on ducted airflow whereby the Betz Limit no longer applies. Redirecting fluid flow is difficult but we do it all the time in jet engines.
Have no fear...the space-time continuum will not lose its flux capacitance and the new Star Trek movie will still be in theaters May 2009.
It is not duct flow downstream. The wake created by this should be significantly greater than that of a similarly sized conventional turbine. You would have to space them farther apart if you have more than 1 row of them. Meaning that even if you could space them closer together, you still wouldn't most likely be getting a better value for your acreage.
Every wind farm picture I've ever seen only has a single row of windmills, usually along the top of a ridge. Is this not the most common distribution?
What makes you so confident that the wake will be greater with the ducted design?
The "scalloped edge," as you call it, is part of something called a mixer-ejector. It mixes the faster air from outside the shroud with the air inside that was slowed down by the turbine blades. The way it mixes the two air streams creates vortices that make it possible to have a shorter duct (by increasing the interaction between the slow and fast air streams).
The Betz limit was calculated specifically for open-bladed turbines.
It's not the design of the device itself that I'm saying is bilge, it's the claims for it made in the video and article. They're totally bogus.
Whether the turbulent diffuser enables this device to work more effectively than earlier efforts in the same direction design remains to be seen. It's at least plausible.
If one defines the Betz limit only with respect to the diameter of the turbine or fan blades, then yes, it doesn't apply for a ducted fan. That's why I used the more general term "area of influence". The diffuser shroud can make the turbine "appear", to the wind, do be larger than the diameter of the fan blades. But the principles from which the Boetz limit was derived still apply: to extract power, you have to slow the air flow. And the more you slow it, the more faster moving air in the upstream flow will divert around the obstruction. Think of cars on a 6-lane LA freeway; if cars in the middle land are slowed to 35 mph at some point (by, say, a bad stretch of paving), you can't have all the cars in the lane behind them continuing at 70 mph without changing lanes.
What's true for an individual wind turbine applies as well to any wind farm as a whole; the amount of power it can produce depends on its area, and no tricks with shrouded fans or turbulent mixing can circumvent that limitation.
all these arguments are very reminiscent of the "proofs" that airplanes cannot fly, and other such wonderful historical footnotes.
there are many examples of inventions that "broke the rules", such as the jet engine or the laser or the transistor. (and there were even more hoaxes along the way.)
the best answer to both the promoters and the skeptics is to try the device and see what it can do. as groucho might have said: "keep an open mind, but check your fly."
I have a funny feeling about this one too. I don't see how you can extract energy from the flow and have the outlet velocity be greater than the inlet.
Maybe they are using their jet engine models and didn't get all the pluses changed to minuses ;)
Perhaps someone with better fluids knowledge can explain.
the jet like design with many blades offered has much more material capacity, hence much heavier and expencive then conventional two/three blades wind turbines 8-(
Has anyone contacted the Picken's Plan people with information of this product? It seem to me that this technology is right up their alley.
They talk about 10 kW prototype and a possible 1 MW turbines. What about even larger turbines of more than 3 MW or lets say 5-10 MW which are needed for large scale (off-shore) wind farms?
This design is interesting but has at least one important disadvantage: much lower swept area. That means less energy harvest per turbine. Personally, I expect more from small improvements on the tried and true multi MW three bladed windmills, rather than a radical departure from it. Tubercles, variable coil generators, laser optics, longer blades, bigger hub height. That sort of stuff.
how does the title related to the article?
The technology sounds interesting but the article is a little misguided in my humble opinion.
How does this discussion about changing blade technologies lead to a halving of the costs? It seems to be a pretty wild assumption to say that this blade design with equivalent power output will cut costs that dramatically...
There are so many misinformed comments on this thread.
1) The article never stated that the air leaving the system was going faster (or even the same speed) as the air entering. In fact, it says precisely that the "faster" outside air is "mixed" with the slower "inside" air leaving the center cowl containing the turbine. If you think it through, this can only be done because of the cowled design keeping the air mass being used to spin the turbine confined and then allowing entry of some of the faster outside air (remember, it's faster than the air hitting the turbine "because" the turbine slowed it down") to actually create a suction.
2) Cost per system. How presumptuous to not believe that these systems can be manufactured at a cost/unit energy less than current air blade designs. Where have you been for the past say.... 50 years!
3) Spacing - Doesn't it makes sense that if these systems aren't deflecting air to the sides that systems could be placed closer together?
Who is writing these comments? And what about the genius quoting on the laws of physics? While I'm not sure FlowDesigns has "broken" any laws, at the same time clearly this commenter has not kept up with his history and read about all those that seemingly had "broken" the laws of physics and now we adhere to the laws these rebels have written.
You know the old saying - Those who can will! Those who can't... will continue to wine about the former.
The DAWT re-visited. Indeed an innovative new configuration. But food for thought and perhaps some science controversy. note the inventors claims (copied verbatim from WIPO patent)
8. An axial flow wind turbine comprising: a. an aerodynamically contoured turbine shroud with an inlet; {sic}.....
d. means for consistently exceeding the Betz limit for operational efficiency of the axial flow wind turbine, wherein the means comprises
full speed ahead..good luck
Innovative Wind Turbine Design
Excellent Wind Turbine design with high efficiency. Such things are needed in Developing countries.
Dr.A.Jagadeesh Nellore(AP),India
Wind energy Expert
E-mail: anumakonda.jagadeesh@gmail.com
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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amills61
1 Comment
A good dose of history first
Lots of attempts to make this type of technology work - it's worth a comparison to the previous trials to judge the new design:
http://www.ifb.uni-stuttgart.de/~doerner/diffuser.html
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phoenix
172 Comments
Re: A good dose of history first
If a good dose of history on the subject of windmills is just what the doctor ordered, amills, just Google it. You will find that this technology can be traced back to the 1100's. Researching the historical background of any subject, which you might find interesting, is always a good place to start.
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Kevin Bullis
178 Comments
Re: A good dose of history first
As the article says, the idea of a ducted design isn't new. But the use of something called a mixer-ejector, see comment below, is new.
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arnetwork
85 Comments
Re: A good dose of history first
Try following the link on the animation referenced in the T.R. article. It is the most unfriendly and incompetent web site that I have ever seen. I tried to send them an email about their site but it is so poorly done I don't know if the message got sent or not.
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Kevin Bullis
178 Comments
Re: A good dose of history first
Are you referring to the Flodesign website, or to this one? The link to the video with this article seems to be working.
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Brittany Sauser
46 Comments
Re: A good dose of history first
arnetwork,
I have checked the link and am not encountering any problems playing the video. I am looking into any technical issues that may have occurred when you tried to view the video. At the very bottom of the page is a "Feedback" link (http://www.technologyreview.com/cust/feedback.aspx) where you can send any issues or complaints. You can also email me directly as I would like to hear the details of the problem you encountered: brittany.sauser@technologyreview.com.
Thanks,
Brittany Sauser
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