Vertical Turbines, Packed Tight, Boost Power

The trend in turbine design has been toward taller and bigger, as the wind power industry tries to maximize generating capacity. But researchers from Caltech suggest the developers might be going about it all wrong – they say much shorter vertical-axis turbines, placed in a tight array with each turbine turning in an opposite direction to its neighbors, can be at least 10 times as efficient at capturing the wind power in a given area.

John Dabiri, a Caltech professor of aeronautics and bioengineering, and his colleagues base their theory on work done at the university’s two-acre experimental wind farm in northern Los Angeles County, and describe their findings in detail in the July issue of the Journal of Renewable and Sustainable Energy.

Vertical-axis wind turbines, Caltech

image via Caltech

Dabiri began exploring the possibilities with vertical-axis wind turbines (VAWTs) after recognizing the inefficiency of the common horizontal-axis turbines (HAWTs) – not individually (they’re actually quite efficient individually), but together in their typical positioning. HAWTs need to be spaced widely to avoid clipping each other, and they also lose efficiency when they create wakes that disturb the turbines around them. In these traditional wind farms, “much of the wind energy that enters a wind farm is never tapped,” Dabiri says.

Vertical-axis wind turbines, Caltech

image via Caltech

The VAWTs Dabiri and his colleagues tested – described by Caltech as looking like upright eggbeaters – were just 10 meters tall and 1.2 meters wide. That’s puny compared to the traditional industrial turbines, which have blades often more than 40 meters long and typically stand well over 100 meters tall. But Dabiri says there’s more than enough energy available in the wind at the lower heights, and by using the much less expensive VAWTs – “smaller, cheaper and less environmentally intrusive,” according to Caltech – we have a much better chance of capturing that available energy.

UPDATE (April 2013): This story was edited after its original publication in July 2011 to clarify the use of the term “efficiency.” In addition, further testing in 2012 appears to suggest Dabiri and his colleagues are on to something with this concept. They report that 18 of their eggbeaters, operating over nine continuous months to April 2012, “produced more power per land area in 5.1 m/s mean wind than 100-meter tall HAWTs in 8 m/s wind.” As the graphic below notes, the researchers believe their turbines could do even better with the addition of high-wind power controls that would allow the turbines to continue to produce power — instead of shutting down — at high wind speeds.

image via Caltech

image via Caltech

UPDATE 2: (February 2014): Those interested in this concept will very much want to see Professor Dabiri’s lecture last fall at the Midwest Mechanics Seminar. It runs for 40 minutes and is available here.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.

  • Anonymous

    This is cool technology.u00a0 Let’s put it to good use.n

  • Desertmama1

    It would be interesting to see how these effect wildlife.

    • Stuart Smith

      Agreed however, does not nuclear, gas, smog and other such things kill wildlife, the planet etc?

    • Joe Edwards

      I don’t see anyway they can effect wildlife unless you clear cut large areas to make them. There is no damage to the environment as far as I can see.

      • Peter Eng

        I think “how these affect wildlife” should include “do we get pureed bird” as part of the consideration.

  • Stevie Beeing

    The question remains, what is the difference in up front investment?

    • William A. McDonald

      I think the part where they said cheaper than the current system we use to manufacturer and setup kind of answered the important part of that question.

  • Michael Clark

    Good idea !! I saw an add on the net for vertical wind turbans with
    3 curved vertical blades about 5 foot tall an 2 foot wide that would mount on a
    pole or the crown of the house.. The 12 or 18 volt version was like a couple
    grand $$$ However 110 volt version was like over $ 20,000 each Wow!! what
    happen? I was thinking one at each end of the house on the roof along with
    solar. My house currently runs on solar in the day and sends back to the grid
    what we don’t use..

    The ones I saw needed 7 mph sustained wind to generate power..

    It was a good idea but $ 40 Thousand bucks is out of my league..

    The solar was $ 18 K and works great..

    Michael Clark in Palm Bay Florida

    • Pete Danko

      Michael, if you are considering investing in home wind power I highly recommend spending a few bucks on Paul Gipe’s “Wind Energy Basics,” a highly respected book that is very, very skeptical of any roof-mounted system. Unfortunately, they rarely measured up to hopes. You might also check out the Small Wind Certification Council’s website:

    • Joe Edwards

      Although wind turbines have been around for quite some time, it’s really no that long in the grand scheme of things. It seems we still have a ways to go before we perfect this method, but once we do the price and efficiency should greatly improve.

  • Mike Barnard

    It’s interesting, but Dabiri has a fundamental assumption which is incorrect which leads him to overstate the implications of his findings. He is convinced that energy density of generation is a useful metric, and that HAWTs aren’t dense. Specifically, he uses 100% of all land area upon which wind farms appear as opposed to the much more accurate <1%-2% of actual land required by the HAWTs, utility roads and related infrastructure.

    As such, his 10x better metric is actually 10x worse, as his arrays preclude any other land use.

    I'm also of the opinion that they will not work well on ridge lines due to loss of laminar attachment of air that taller VAWTs are not impacted by, but Mr. Dabiri disagrees with me there, although he hasn't performed tests and studies as yet.

    His math also depends on massive economies of scale not currently achieved in VAWTs due to their relatively lower efficiency and effectiveness.

    He is finding results, but lets not oversell them.

    • Antti Pietikäinen

      But VAWT can take advantage of direction changing turbulent winds, whereas HAWT has to turn towards the wind am I right?

      • Mike Barnard

        Certainly, but turbulence is always accompanied by low velocities and the power in the wind increases with the square of the increase of the velocity. For example, a 10 kph wind is 16 times more powerful than a 6 kph wind. Utility scale HAWTs are high off the ground in strong and steady winds with low turbulence, so get a lot of power from the wind. VAWTs near the ground are in much lower speed / force winds and turbulence sucks more energy out of them.

        There’s a reason why even in the small wind energy space, four of five wind generators are HAWTs, with only the UGE being on the list, and that’s mostly because it’s pretty.

        • Pete Danko

          I’m still waiting for a VAWT to gain Small Wind Council certification. A couple of UGE models have been “under test” for quite some time… h

    • christianh

      You’re being a bit too critical… It’ snot a competition it’s a compendium of ideas… My Senior project in ME school was a VAWT.. We got pretty good power generation at 50ft using helicopter blades around 20 foot diameter… Certain areas that aren’t feasible for HAWTs would welcome these, such as dense housing areas or perhaps Central Park..

      Any wind energy is better than none…

      • Pete Danko

        I get your point that experimentation and exploration is necessary. But in truth, the search for cleaner alternatives to fossil fuels *is* a competition. You might be willing to invest in a wind turbine or turbine array based on “any wind energy is better than none” but to make a meaningful difference, it will need to do better than that.

      • Mike Barnard

        My critique is due to his faulty assumption, which is difficult to read as not attacking the most effective form of generating electricity from wind that we have found. Mr. Dabiri chose to differentiate his research with unfounded claims which have been picked up on by anti-wind protesters.

        As for VAWTs being suitable for some niches, sure, but most places that they are considered for will still get better performance out of HAWTs.

        New “innovations” in wind power usually aren’t. The most effective form factor for harvesting energy from the wind is the three-blade, horizontal axis wind turbine. Alternatives have all failed to be economically viable, that’s why there are about 250,000 tall, graceful wind turbines around the world today instead of other technologies.

        • Bill McEachern

          That is far from the whole story. the main reason that 3 bladed upwind HAWT’s are the “commercial standard” is that when the wind energy subsidy in Ca. changed from a capacity based to a production based incentive the most reliable machines at the time were the 65 kW 3 bladed upwind machines from Denmark. In order to capitalize on the incentive in the early 1980’s the wind developers in Ca made this item Demark’s biggest export – outstripping ham. With that flood of money the HAWT’s of this configuration became the dominant type. The largest machine in production at the time though were the Flowind VAWT’s at 225 kW. The reason they went “unreliable” was that the aerodynamicists at Flowind wind insisted on counter sunk fasteners at the blade splices and the roots. Those counter sinks were badly executed leaving a knife edge at the bottom of the hole. Given the far more unforgiving dynamic nature of VAWT’s this yielded fatigue failures in the baldes. Had the the decision gone towards protruding fastener heads the current wind turbine scenario may have been decidedly different than what we see today.

    • Chris Golightly

      I do not understand why you say that energy density is not useful or why that assumption is “fundamentally incorrect”. Offshore we are finding that high, bigger 5, 6. 8, even 10 MW top heavy HAWT 3-bladed so-called “turbines” are just getting too expensive to for us construct in water depths over 30 m on huge steel 900 Tonnes+ monopiles and jackets. Building what are essentially onshore turbines in a more demanding offshore environment is just not going to work and we will need a major step change to floating VAWTs in 30 to 100 m WD. lower and more closely packed to move forward and cut costs. This will require new industrial entrants from the Oil & Gas and Aerospace industries, which is most likely to occur when the time is right. The current crop of “status quo” HAWT propeller manufacturers and other vested interests do not like to hear this little tune being played do they Mr Barnard?

      • Mike Barnard

        My apologies, but you have introduced a completely different and irrelevant argument to the discussion. You haven’t touched on the core question of energy density at all.

        • Chris Golightly

          Yes I did, I asked you why you thought “Energy Density” was not useful. Others will decide on the irrelevance of my other statements. In addition everyone has a right to introduce new linked topics or arguments into a discussion site. You have been very critical of the excellent work of John Dabiri, who is one of a few (and best) researchers helping the offshore wind industry move away from expensive top heavy HAWT land turbines provided by a few manufacturers towards smarter floating closely packed lighter VAWTs, which will be very much easier to transport and construct offshore in large quantities. There are reports nor from Sandia Labs and the NREL indicating this. In addition, if any reader cares to Google SKWID or NENUPHAR they can see what the Japanese and French are up to out at sea with floater VAWTs, backed by national governments and major industrial players. Have a nice day now!

          • Mike Barnard

            Umm… I explained why energy density is a meaningless measure, but I’ll try again.

            First, no one makes decisions on generation technologies based on how many square feet that they take up. Economics are partially impacted by that, but not entirely. This is an argument from the nuclear industry folks, but it’s kind of silly because no one except them and anti-wind guys actually think it’s important.

            Second, Dabiri ignores all of the space between HAWTs in his calculations. In flat land farm areas, wind turbines and all related infrastructure take up less than 1% of the area that they are spread over. They typically take a quarter acre or perhaps a tenth of hectare for their bases, and more for access roads and transformers. The rest of the land between them has exactly the same economic value it had before. If they were growing high value crops, they get almost exactly the same amount of crops. If they were grazing cattle, they get almost exactly the same amount of cattle feed. His arrays require 100% of the area that they take up, and leave no room for any other use. He’s comparing 100% consumption to 1% consumption as if they are equal. It’s a false comparison. It’s 2% on ridgelines, but the same discussion applies. His claim of 10x effectiveness is just as silly as claiming the opposite based on the 1% number, that HAWTs are 10x more effective than his arrays. It’s a meaningless measure.

            This isn’t even a controversial statement except for those looking for ways to attack HAWT technology.

            Third, energy density of the wind is based on velocity, with energy increasing by the square of increases in velocity. Dabiri’s tech uses 10m tall VAWTs, well below the level at which laminar flow turbulence substantially slows the velocity of the wind. Taking a 3MW Vesta as an example, the swept area is from 60m to 150m, heights where the wind is much stronger, giving a much larger impetus to the blades. Dabiri’s VAWTs get more energy out of the much less energy closer to the ground, but just don’t have as much energy to harvest.

            Fourth, ignoring the velocity of the wind and only looking at the swept area, Dabiri’s tech runs into another problem. To achieve even swept area equality with a big HAWT would require an array of HAWTs over a kilometer long and ten VAWTs deep (a sniff test maximum for energy capture for the arrays). That quarter acre really equates to a much larger surface area being consume to achieve equivalent potential air capture.

            Fundamentally, he’s getting better performance out of VAWTs using the array principle, and I’m all for that. I wish him well. But the energy density argument is bogus and I’ve had an extended discussion with him about it. I assume that eventually his innate intellectual honesty and integrity will make him stop making that claim, but as of the last time I spoke to him, his intellectual ego was still in control. That’s okay, reality will prevail.

          • Chris Golightly

            Mike, No need for the supercilious “Umm”. You have done that twice here now. You may not have experience in the offshore industry, which is different. We use energy density a fair bit, although not exclusively. Nobody thinks it is “silly”. Our situations are open water which requires economics other than farmland. The work done as backed up by Sandia shows that in almost all circumstances, floater VAWTs closely packed and yes, shorter will provide more energy thruput. The Japanese are doing that and they are not stupid, except when it comes to the design of the height of their anti-Tsunami walls. Our problem is that we do not yet have twin or triple blade Darrieus turbines that do not rattle itself to pieces and destroy their bearings in our wind and wave profiles and we do not yet have the means for genuine taut tether damped oil industry FPSO style tension leg moorings. Not easy to solve, but if we do not, you can be assured that the offshore wind business will wither and die as we are starting to see now in European projects.

          • Mike Barnard

            As for the SKWID, it’s kind of interesting, but the first prototype is apparently just being installed and the output is pretty low. The spec sheet specifically calls it out as being designed for isolated ocean outposts, not utility scale generation for the grid. They are targeting a niche, not pretending that they are an alternative.

            The Nenuphar site has been static for two years. They are dead in the water and the site is a historical remnant now as far as I can tell.

            My apologies, but solitary VAWT tech just isn’t that interesting. That’s why there are about 250,000 HAWTs generating utility scale electricity world wide and about 0 VAWTs generating utility scale electricity worldwide.

            Sandia Labs report on arrays of VAWTs was from the 1980s. NREL isn’t assessing them as far as I know. Please provide links if you know otherwise.

          • Chris Golightly

            The SKWID VAWT selected is a poor choice. German and UK offshore projects assuming conventional land HAWTs of 3.6 to 6 and 7 MW are in danger of falling like flies as we speak. Nenuphar is delayed until 2014 and is not “dead” but is slow.

  • Orlando Fernandes

    Energy-XS has an award winning VAWT with a COP of .59 check out

    • Mike Barnard

      Ummm… no. Orlando aka Energy-XS is just making two models of Darrieus-style wind turbines (he is the only person named in the award from the DST-LM website). He is also claiming that making another permanent magnet generator is an innovation. He isn’t even close to the first to put the two together, and probably not the first to do so in India.

      And if by COP he means coefficient of performance, Betz’ Limit is 59.3% and no VAWT including these get close to it. HAWTs get much closer, and this has been well understood since the 1960’s.

      I don’t see any claim on their website to this, but I do see some fascinating videos of their wind turbines spinning indoors with no apparent through breeze. I can safely say that manually spinning the blades then stepping back to take video of the results isn’t a viable generation strategy.

      The site that states that they won an award shows that it was given to Orlando Fernandez, as above, but provides zero reason as to the basis of the award. He seems to be a reasonable self-promoter however.

      • Orlando Fernandes

        Rethoric aside, this might not be the forum to discuss IP.

      • Orlando Fernandes

        Rhetoric aside, this might not be the forum to discuss IP. We might not be the only ones in India, but certainly the first to exploit VAWT’s starting over six years ago.

        • Mike Barnard

          VAWTs are very well understood technology world wide. Making claims about extraordinary efficiencies from them also has a long history.

          The only standards that are acceptable for remarkable claims are independent testing by qualified test labs and full-lifecycle cost analyses following ISO standards.

          VAWTs have a small niche. It’s good that you are building them cheaply in India for small scale local generation. India needs a lot of distributed power given the challenges it has with its grids. But understand that the technical limitations of VAWTs are well understood and can’t be resolved on an individual scale without changing fundamentals of physics.

          Dabiri’s research is interesting as it uses interactions of VAWTs to achieve greater output. But he understands that the individual VAWTs need to be dirt cheap and simple in order to make it cost effective.

          • Boloar

            No offense, dude (isn’t it amazing how many things start out with those words, and yet to little effect? …)
            Having actually met Mr. Orlando Fernandes and observed his work, I call on you to please have some shame and not assume that what you know is all there is to the discussion. I don’t care if you think you are simply sharing your opinion, but you are coming across as a purely self-righteous, entitled, smartass white dude. I lived in America for a time and met enough of them to last a lifetime. Please stop.

            I’ve seen the numbers Energy-XS has recorded and his take on the design is quite fairly impressive. I can’t say more, unfortunately, without compromising his intellectual property. As a small company, there are significant hurdles for them to overcome in making this mainstream technology in India, but they are well on their way. They were the first to explore VAWTs as a business possibility in India, even if others are doing so now.

          • Mike Barnard

            No offense taken.

            All he has to do is get an independent test lab to validate those numbers and publish them along with sufficient information for a comparison to be made. And then it will be obvious that he’s made just-another-VAWT. Until that time, like every other attempt outside of Dabiri’s to make VAWTs be something that they aren’t, it’s lipstick on a pig.

            Refusal to share IP is a smokescreen behind which many things can be hidden. Protection of IP is a well-understood field. Six years is more than long enough to adequately protect the IP.

            If after six years there is no protection except not telling anyone what the secret sauce is, not publishing the secret sauce in a peer-reviewed journal, not exposing the secret sauce to independent analysis and verification, then it’s remarkably safe in the wind energy biz to say that the secret sauce is a marketing ploy. Dabiri is publishing results which anyone who wanted to could attempt to replicate, results which are accessible for critiquing.

            Listen, I think that Orlanda / XS Energy is selling a completely reasonable, locally built VAWT to a market where that is of value based on my knowledge of India and talking to Indian energy professional and individuals about power there. From reading the XS Energy website, it’s clear that they are selling hybrid systems with solar and storage component as well. Their biggest turbine is 5 KW, which is tiny but very reasonable for households. This is a useful mixed energy system that’s of value in a lot of places in India. I’m all in favour of that.

            This is a very reasonable solution that doesn’t need bogus differentiation. Stick to reality, sell the product, don’t promote numbers that aren’t supported.

            There are several good small businesses around the world that are doing exactly the same thing. It’s a good, clean revenue generator, and it’s more needed in India than in North America or Europe.

          • energydirect

            I am an engineer. I am also a somewhat rare person — I am involved in the US offshore wind power development industry. While I can take issues with a few individual points, Barnard’s arguments are, in essence, correct.

            Neither the cost of a wind farm nor its capacity factor is particularly dependent on land use (of course, in the limits on either side, that statement is no longer true, but we live in the real world). Furthermore, spacing out turbines on land, thus allowing multiple uses, is part of the equation that makes wind power economic.

            Offshore, land cost is even less important. Construction, platforms, trips to the site, maintenance and transmission lines are what drives cost. Notice I didn’t mention the turbine. Therefore, if you can get more energy out of a single structure then cost of delivered energy goes down. In this case, bigger is better. The effective cost of the turbine goes down as it gets bigger (that is, the cost that matters).

            The “bigger is better” thesis for offshore in terms of ROI was also proved by the offshore O&G industry — more wells, one platform, etc.

            By the way, I see lots of references to investments by others in offshore VAWT. Those investments pale when compared to the Japanese, Chinese, and European investments in offshore HAWT.

            Furthermore, the US DOE is investing $150 M in offshore demo projects right now and the private and state investment in those demos will more than double that. And that doesn’t include the DOE investment in offshore HAWT technology development.

            VAWT are interesting. They may be fundamentally flawed or they may someday compete. However, right now, the real investment and the real power generation is in HAWT. Given the technology development curve, it will be much longer than 10 years for VAWT, if their flaws can be fixed, to catch up. Remember, we aren’t building iPads here, we are build power generation stations.

          • Boloar

            As I was careful to note in a prior comment: comparing VAWTs and HAWTs is an apples/oranges comparison.
            I haven’t disagreed with any of Barnard’s facts, but I will contest to the death the idea that HAWTs are the only feasible way to go about wind power, especially considering what I saw of Orlando’s / Energy-XS’s operation, and based on the promising characteristics of this guy’s (Dabiri’s) study. Not being a mechanical engineer myself (nor pretending to be one, unlike some I can think of), I can’t comment reliably on the physics of it.
            At any rate, no one has proposed a solution to the intellectual property thing that is the actual issue here – not to mention, aside from corruption, that patents in India can take more than 5 years from application to grant.

  • Stuart Smith

    We have the technology to make almost all uses of electrical items minimal, yet we still use 240 volts in this country and in the attempt to build stuff that wears out and is as cheap as possible to manufacture they are not efficient.

  • Andreas

    What’s the 20-year LCOE including O&M costs such as power control, monitoring and parts replacement?

    • Pete D

      Way too early in exploring the concept to know that, but Dabiri does briefly address those issues in the lecture linked to in Update 2 at the end of this story. I recommend the entire lecture (40 minutes) but the cost discussion comes from 36:40 to 37:20.

  • Joe Edwards

    It would be cool if we could design them to look just like trees, and every leaf could be a little blade to catch the wind, this would solve the issue of being environmentally intrusive.

  • da5650

    100m turbine technology will go by the way of the dinosaur

  • Jed Bland

    Trouble is there’s as much money to be made building and installing them.

  • Bill McEachern

    There is no doubt that VAWT’s in particular and wind turbines in general are much more complex machines, primarily due to their inherent vibration environments, than lay people think. Your failure to realized that what Mr. Barnard is saying is correct, regardless of any bias on either side, and it has been proven to be correct for many many years is not doing yourself any favors. You might want to read a paper by South, Mitchel & Jacobs entitled Strategies for Evaluating Advanced Wind Energy Concepts from 1983. It was a SERI/DOE report.
    On the whole land use argument: wind turbines are swept area machines full stop. They are not sized by land use and generally land use is not significantly affected by their presence.
    The old arguments that favored VAWT’s over HAWT’s were of the square cube variety – when machines get really big the blades of VAWT’s had theoretically better odds as they were supported at both ends. The cost of entry given the technical risks has so far been unattractive to seriously attempting a really big VAWT machine not to say one hasn’t been built. the 4 MWe Eole project was one but it was not a serious production machine – everybody knew it was going to not work for long before it even went up. Such is/was the government funded mentality of bureaucrats selling big budget projects to further their careers. I believe it was the world’s first variable speed machine as well – which is now pretty common but at $35 million they would have been very much further ahead had they concentrated on perfecting a 500kW machine which was not terribly far from reality at the time if the $35 million had gone towards that aimed at an outfit that wanted to be a wind turbine manufacturer rather than an executor of government work. Denmark had a very much better government policy and they had expensive power fueled by oil. Canada on the other hand had, at the time, some the the world’s cheapest power, wind not very close to consumption and utilities that liked Nuclear, falling water and coal of which they had ample in low cost supply. C’est la vie.

    • Boloar

      “Your failure to realized that what Mr. Barnard is saying is correct” …
      My good man – please find, and quote for me, precisely where I’ve said he is wrong. With the failure of that one sentence, the rest of your discourse is redundant. I appreciate the thought, though.

      I was very careful to note (please, go check) that comparing HAWTs and VAWTs is an apples/oranges comparison. I am also aware of the limitations and strengths of each. The difference here being, however, that I have *seen* something new, i.e. Mr Orlando’s work, and seen the details he has recorded. And that goes back to the original point of IP being why I am not comfortable sharing details of somebody else’s promising work. If someone can address that issue (in the context of India, not the first world), then that will be a constructive use of this thread.

      I am careful to say what I mean, and what I’ve said here – grossly oversimplified – is: please don’t converse in a way that assumes established technologies should be the end-all and be-all of the discussion, the way Mr Barnard does. At least consider the possibility that something new can come up. Being dismissive about others’ work and/or ideas, as he is, is often more offensive than outright disagreement.

  • Cuss

    These numbers would indicate that the VAWT would be much cheaper per unit than the HAWTs currently in use.
    “The VAWTs Dabiri and his colleagues tested – described by Caltech as looking like upright eggbeaters – were just 10 meters tall and 1.2 meters wide. That’s puny compared to the traditional industrial turbines, which have blades often more than 40 meters long and typically stand well over 100 meters tall.”

    • Pete D

      These VAWTS would indeed be less $/turbine but the question would be regarding $/watt. Dabiri believes there could be economies realized with the VAWT, but that remains to be seen.