Why aren’t vertical-axis wind turbines more popular?

Last update: August 9, 2014

Some groups and individuals tout alternative technologies for wind generation, especially vertical- as opposed to the horizontal-axis wind turbines normally used.  They make a variety of claims about power generation, noise, bird friendliness and others that in their minds make it a superior technology.

So why aren’t vertical-axis wind turbines (VAWT) in their various forms more broadly used?

Short Answer:

Vertical-axis wind turbines trade one set of compromises for another, and typically not favourably. They typically require twice the swept area and four times the material to generate the same electricity as horizontal-axis wind turbines. At this point, no one has been able to make the balance work out in their favour except in niche roles. And, frankly, they are solving non-existent problems.

Long Answer:

It’s worth starting with some examples of the various forms of vertical axis wind turbines out there.

Here are a couple of examples of refined vertical-axis wind turbines with aerodynamic blades:

There are less efficient and refined wind generators as well, based on very old principles such as the Savonius design (named for a Finnish engineer who created a variant of it in 1922), examples of which are shown below.

Simple drag vertical-axis wind turbines have a long history, and a version was used as the first electrical generating wind turbine ever, built by Professor James Blyth of Scotland to power his holiday home in 1887.

Screen Shot 2013-02-22 at 9.49.48 AM

Here, for comparison, is a set of offshore, highly refined, triblade, horizontal-axis wind turbines (HAWT):

Their primary characteristics are three aerodynamic blades facing the wind and rotating around a horizontal axis.

VAWT Proponents Overstate Advantages

1. Utility-scale wind farms are set up where winds are relatively stable, so catching the wind from any direction isn’t a particular advantage.

Proponents and inventors claim that VAWTs catch the wind from any angle, making them more effective than HAWTs.  Catching shifting winds and eddies from any direction is only an advantage in small-scale situations such as urban or rooftop settings.  Horizontal-axis wind turbines (HAWTs) are set up in areas with steady winds and the blades are well above ground turbulence that causes variable eddies.  VAWTs’ advantage is only in niche environments. [2]

Coast wind farm courtesy of Green is Sexy

2. VAWT blades are rarely at an optimal angle to the wind or in clean air, so they can never be as efficient as a triblade HAWT and won’t generate more electricity

Proponents and inventors claim that VAWTs generate more electricity than HAWTs.  Point 1 above dispels this, but what else comes into play? Energy generation is a factor of surface area of blades exposed to wind plus aerodynamics of the blades (plus other factors of diminishing returns).  4.5 MW HAWTS have massive spans with lots of blade surface catching wind, very aerodynamic blades (with variable pitch and surface area along their length to account for varying speeds) and the three-blade standard allows relatively clean air for them to spin through as the wind carries blade eddies downwind before the next blade passes through.

This diagram provides one perspective on how HAWT blades are operating in clean air.

For another perspective, I created this simple graphical illustration.

Screen Shot 2014-08-09 at 8.11.06 PM


VAWTs on the other hand have extreme difficulty achieving the same balance of surface area, aerodynamics and ‘clean’ air for best laminar flow.  The majority of the time the blades are not presenting optimal surface area to the oncoming wind, but rather very sub-optimal surface areas. Only the blade in the very front is in clean air; as the blades rotate, they pass into very turbulent air with much lower efficiency of aerodynamics.

This graphic clearly illustrates the turbulence blades to the rear of the device pass through.


At least one commenter is dissatisfied with this clear illustration, so I developed this graphic to push the point home more clearly.

Screen Shot 2014-08-09 at 8.10.34 PM

The odds that a VAWT of equivalent area will generate as much electricity as a triblade HAWT are virtually nil, and they typically will use four times the material to generate half the electricity for a given swept area resulting in a low lifecycle cost of electricity. [2], [5]

3. HAWTs almost never collapse due to lateral stress, and VAWTs typically have very asymmetrical front and rear stresses on their bearings

Proponents and inventors claim that VAWTs produce less stress on the stalk. This is engineering and economics.  HAWTs collapse extremely rarely; the engineering is very sound and the full-lifecycle cost analyses show that they are actually the fastest payback form of electrical generation in the world. At present, VAWTs don’t generate enough electricity that the full-lifecycle accounting shows them to be advantageous on a cost or materials basis over HAWTs. What problem are they solving? [1], [5]

4. HAWTs have been getting quieter as they get larger, and modern wind farms generate 10 times the electricity with less total noise than older wind farms

Proponents and inventors claim that VAWTs are quieter.  This is unproven actually. The first larger scale, 2 MW VAWT prototype is just being constructed; noise characteristics are undefined as yet.  And of course, HAWT refinements continue to keep noise emissions at the same level or lower despite massive increases in size; a 4.5 MW wind turbine is only a dB or two noisier than a 1.5 MW wind turbine, which is much quieter than older 600 kW wind turbines.  And 4.5 MW wind turbines are spaced much further apart than smaller wind turbines, so the total environmental noise is actually much less for significantly greater power output.  Wind energy is actually remarkable in that it is actually quieter the bigger the generation factor.  This is not true for any other from of electrical generation. VAWTs aren’t proven to be quieter and are competing with technology which is already very quiet. [3]

5. To generate the same electricity, VAWTs would have to be as tall as HAWTs, so visual impact will be virtually identical

Proponents and inventors claim that VAWTs have lower visual impact. This is only true for smaller wind generators, closer to the ground, which would be true for smaller HAWTs as well. This is trading off making it less conspicuous for making it less productive which isn’t particularly useful.  To make them economic for grid-scale generation, they would have to be so big that they would still be very, very visible.  VAWTs only really lower visual impact in some cases as some designs are sculptural objects that happen to move, but this is also a very subjective point.

6. Shadow flicker is only a problem at dawn or dusk for few minutes a handful of weeks out of the year for any given home near a wind farm

Proponents and inventors claim that VAWTs don’t generate shadow flicker that is problematic, as that is a factor of the triblade design.  Shadow flicker is a vastly over-stated problem. It will only occur for a few minutes at sunrise or sunset for a week or two twice a year at residences near wind farms. HAWT rotation is too slow to cause epileptic seizures (and there are design studies and standards to ensure that this is true). Wind farms typically try to assess their impact on local dwellings and adjust where possible, and all three major wind farm siting tools —   WindPro, WindFarm and Windfarmer — includes shadow flicker modelling. Anti-wind advocates drum it up, but you pretty much have to be looking for things to hate about wind turbines to think it’s a problem.  VAWTs sufficient in scale to generate utility levels of electricity will still be hated by NIMBYs. [4],[8]

Screen Shot 2013-02-23 at 12.04.30 PM

7. If all fossil fuel generation were replaced with HAWT wind farms, million fewer birds would die annually

Proponents and inventors claim that VAWTs will kill fewer birds than HAWTs.  As HAWT bird mortality rates are typically vastly overstated and are much less than fossil fuel generation, lighted windows, cats, transmission lines, cars and many other sources of avian mortality, this is a straw man argument.  As VAWTs scaled up the utility generation capacity have not been built or compared for avian mortality, it’s a straw man argument without merit, similar to the noise problem. [7]

Horizontal-Axis Wind Turbines have additional disadvantages

1. VAWTs typically aren’t high enough off of the ground

The major innovation that has maximized wind turbine capacity factors and generating ability is that they have been getting taller. Laminar flow physics slows the wind down the closer you come to the ground (which I’ve experienced viscerally while paragliding).  VAWT designs have the blades much closer to the ground than HAWTs, so they are losing significant amounts of wind velocity. In order to overcome this, they have to be much higher up, and lose most of their purported advantages. [2]

Eggbeater VAWT guy-wired to ground

2. HAWTs work very well

There have been vertical and horizontal axes wind turbines around for decades.  There are about 240,000 horizontal axis wind turbines generating electricity in the world today and they are now operating at 35%-47% capacity factors because they are a proven, tested and constantly refined technology. [1], [6], [10]

Screen Shot 2013-02-16 at 8.01.30 AM

3. HAWTs have economies of scale

The corollary to HAWTs being the winning technology for all of the reasons listed is that there are very well optimized and integrated supply chains that allow specialization for different wind conditions and good pricing. If VAWTs were actually solving a significant problem, there would be incentive to create subsidies to shift the market, but they don’t actually solve sufficient problems to make them worth subsidizing. [1]

There is one model of VAWT that has a specific claimed advantage in that it self-stalls at 27 meters per second, allowing it to be used for small wind generation in areas with frequent very high winds.  Of course, utility-scale HAWTs have control systems that automatically brake and feather the blades in these circumstances without an problem whatsoever, but small-wind HAWTs typically do not have these control systems.  A niche, but worth considering.  [9]

Testing by the Sandia Lab confirms all of the above in side-by-side tests of VAWTs and HAWTs, finding that VAWTs will produce 15-25% less electricity for the same swept area with likely higher costs. [11]


[1] How effective are wind turbines compared to other sources of energy?
[2] The wind doesn’t blow all the time. Why doesn’t this make wind power ineffective?
[3] Humans evolved with infrasound; is there any truth to health concerns about it?
[4] Wind farms don’t make people sick, so why the complaints?
[5] Quora: What are the parameters involved in making a wind turbine blade?
[6] Wind turbines pay back total environmental ‘debt’ in under six months
[7] How significant is bird and bat mortality due to wind turbines?
[8] UK Shadow Flicker Evidence
[9] http://re-innovations.co.uk
[10] http://www.gwec.net/global-figures/wind-in-numbers/
11] http://www.wind-works.org/cms/index.php?id=43&tx_ttnews%5Btt_news%5D=2220&cHash=b55932dfebd049ab01c1d968670afc1e

See also:

  1. http://www.wind-works.org/cms/fileadmin/user_upload/Files/Jim_Tangler_VAWTs_AWEA2000b.pdf
  2.  Are airborne wind turbines a plausible source of cheap clean energy?
  3. Quora: Why is ocean energy used so seldom?
  4. http://www.motherearthnews.com/Renewable-Energy/2008-02-01/Wind-Power-Horizontal-and-Vertical-Axis-Wind-Turbines.aspx
  5. http://news.nationalgeographic.com/news/energy/2012/08/120820-helix-wind-collapse/


  1. Jota Efe · · Reply

    This is a well though out, complete overview. Thanks for that.

    I will say though, that for small, inexpensive “home” wind turbines, the tradeoffs are much harder to balance out — brake systems are not as sophisticated on HAWTs, and the noise levels are crazy loud for those small whiny turbines. They are also not as optimally placed for constant wind direction. That is probably where the VAWTs are most appropriate — the second home in cottage country that’s unpredictably windy…

    1. I agree.

      But in that case small wind generation is almost never going to be cheaper than just getting electricity from the grid. Small wind generation isn’t particularly economic unless you are off the grid and willing to live with significant compromises.

      My general recommendation is to invest heavily in insulation and conservation before generation for homes.

  2. Late comment, I know, but I do appreciate the info in this article. Well thought out and researched.
    I agree with the first commenter that there may be a niche place for VAWTs in urban environments, where you can’t get the same height as in an industrial wind farm. Small, micro-scale vertical axis wind turbines may actually perform better than HAWTs, due to varying wind conditions and low start-up speeds.

  3. Sandro · · Reply

    VAWTs have an additional advantage that isn’t yet well known because they haven’t been scaled to utility-levels: fields of VAWTs can be packed more tightly together than HAWTs, so they consume less space for comparable output. This is based on preliminary research, so it remains to be seen if they will scale sufficiently well to outweigh the additional maintenance required.

    1. I’ve analysed John Dabiri’s research on this. He has a fundamental error in a key premise that leads him to state that. He has believed the people who say that wind farms take up all the land that they are sited upon, as opposed to the reality of less than 1% to a maximum of two percent. As a result his math gives the inverse answer to what is actually true: that closely spaced arrays of small VAWTS actually have an order of magnitude less energy density than utility scale HAWTs today. I have an article coming out on another site in the next couple of days and will update the relevant parts of my blog as well.

      The array of closely spaced VAWTS was evaluated by Sandia 30 years ago and never followed up on. Similarly, the 2004 patent by other parties has never been implemented commercially either.

      Dabiri is sincere, brilliant, charismatic and richly deserving of the MacArthur Genius grant. But this is one of the mistakes that will occur when a brilliant engineer works in multiple fields simultaneously. Edison, I believe, said “Fail faster”. Dabiri’s work overall is fascinating. This piece of it is more of an interesting mistake.

      For clarity and references on the land use issue, please see my post in this blog on land density. I’ll update this later when I’m not mobile with bad wifi with a link.

      1. Sandro · ·

        I look forward to your article. Please post a reply here to let me know when it’s up!

      2. Will do. Should be within 48 hours based on editor’s response over the weekend and my turn around last night.

      3. Hi Mike,

        Thanks for your thoughtful commentary on VAWT vs HAWT. I’m very interested in your coming post in regards to Dabiri’s work. I don’t understand your 1 to 2% comment in regards to Dabiri’s work. Dabiri points out that conventional wind farms need turbine spacing of 4 rotor diameters laterally and 10 dia in direction of wind. These seem like very well established numbers in industry. While it may be true that the base of the turbine, or even the vertical shadow footprint of the HAWT is only 1 or 2% of the land in the wind farm, the farm still can’t fill up the space between the turbines, so it’s capacity per acre is limited, as I think all experts agree? In contrast what Dabiri’s shows via what appears to be sound research is that a group of small VAWT turbines may exceed the production capacity of conventional HAWT wind farms by an order of magnitude, measured in kWh’s per acre. I look forward to reading your article on the subject. I do agree with much of your article. What I would add is that VAWT wind turbine designs have been either efficient but not durable (Darius as in the Flo design or Sandia studies), or durable, but of very low efficiency (the Savonius). My interest in this field lead me to a new design, that has been tested by a qualified engineer, and the data analyzed by a grad student, to show that it is competitive with the best small HAWT’s (Bergy). I’ve got some research papers on my website that you might find interesting. http://artturbine.com/relevant-documents/ Best Wishes

      4. Hi Drew …


        I had an extended conversation with Mr Dabiri over email on the land usage point. He was committed to using all of the land over which wind farms spread rather than the actual land they took out of other uses during the debate.

        I expect that his fundamental academic and intellectual honesty will cause him to soften his statements around this substantially.

        I’ll look at your other material later.


      5. Thanks for the prompt reply Mike. Dabiri’s position on this seems reasonable to me? What am I missing? In both cases, high density VAWT farm and MW HAWT farm, the land isn’t substantially affected for other uses? Are you saying that his VAWT farm will take more land out of use? Why would it, and in most cases, where there is significant wind resource, their isn’t much other use for the land, other than farming? The issue as I see it is that if you have a good wind site with conventional HAWT MW, you must let most of the energy pass by, simply because you can’t get enough turbines into it, without them interfering negatively with each other, whereas with tight VAWT Array’s many more Watts/acre are available. With a VAWT array, you should be able to extract substantially more resource per acre. This of course I am sure you will agree is not the primary question around wind, it’s big issue is $ to W, not Acres to W. What Dabiri did show is that using a very high $ to W turbine (with low durability and low efficiency) he was able to extract much more power per acre than wind industry experts expected. This means that if someone comes up with a VAWT, suitable for similar density array’s, that has a better $ to W and high durability, it could challenge the existing model? I think my work goes in that direction, the turbines Dabiri was using have a Cp of .17 according to NREL testing, whereas my turbine has a Cp of .31 according to independent reviews of my work. My turbine is inherently more durable than the wind spire turbines. Further, because my turbine isn’t a series of long spindly foils, that have to resist strong reversing forces, it can be made from much less expensive materials. Thanks for the conversation Mike, I look forward to hearing what you think.

      6. Hi Drew . . .

        Still haven’t got to your specific design, but it’s on my list.

        There are several challenges with Dabiri’s assumption.

        The first is that no one measures energy that way. Cost-of-land is a relatively minor factor in generation decisions, and it varies substantially depending on whether public land is granted, private land is leased, whether the land is arable or non-arable and proximity to urban- or recreational-areas. Watts per acre is meaningless.

        The second is that if you are going to use it, you have to use it in an apples-to-apples way, in other words count the land which is actually required as opposed to the land around it. The array of VAWTs are spaced a couple of meters apart, precluding any other use for the land. HAWTs are spaced hundreds of meters apart and the land between them is useful for any number of other things. Only the land actually consumed by the HAWTs, in other words, should be included in the equation. If it were a meaningful metric, the array of VAWTs would actually generate only 10-20% of the energy per acre of HAWTs. This is equally ludicrous as an assertion.

        Third, the array of VAWTs is restricted in height. At present Dabiri is experimenting with Windspire 10 meter high turbines, and it’s unclear that if scaled up the same vortices would scale in the same way allowing the same effect. He is only capturing the wind below 30 meters in other words, while HAWTs are capturing the wind at 50-150 meters. As a result, he’s taking up a lot more ground to capture the same swept area of moving air, and the air he’s capturing has a lot lower energy density. It’s just as easy to say he’s wasting the wind resource as HAWTs are. It’s another nonsensical argument. When arguing this point with him, I made the following calculation:
        Plucking one reference, the 2.7 MW Alstom ECO 122 has a swept area of of 11,700m2, most of it in higher energy potential air than a VAWT array. Assuming a 4.1m VAWT blade length and 1.2m span, (numbers from your 2010 report) a VAWT has a swept area of 4.92 m2, requiring almost 2400 to cover the same airspace — still of lower energy density wind — as a single 2.7 MW HAWT. And of course, those 2400 VAWTs would be spread out over — assuming the 1.65 diameter spacing, and a maximum of 10 downwind HAWTs in an area (there is a maximum array depth, and I’m being conservative in favour of more) — roughly 700 m long by 30 m deep, or roughly 210 ha for a 2000:1 land usage density.
        Dabiri is finding interesting results which could extend the niche for VAWTs. But he isn’t finding anything which will economically replace VAWTs as far as I can tell.

      7. Hi Drew . . .

        Thanks for pointing me at your design for a wind turbine. I don’t see much new there. Helical VAWTs are pretty common, there are tons of patents for them and many exist in production or prototypes in the wild.

        I like them simple because they are pretty, which helps make up for their fairly significant loss of generating efficiency and LCOE challenges. Yours is quite aesthetically pleasing in the video small scale one. Not sure it would generate enough electricity to be worth putting in a garden, but you could imagine it there.

        And my apologies, but the CP is specifically stated for winds above 10 m/s or 36 kph. Under the same conditions, modern HAWTs achieve 90-95% of Betz Limit, or 48.51% CP+. This is an artificial construct as the wind is not at that velocity at all times. Modern HAWTs, mostly by being much taller and hence in a better wind resource, but also due to enormous incremental innovations in pitch, coating, gearing, etc, are achieving real capacity factors of 35-47% at the best sites in the US and 50% in Brazil. This is empirical data from real world annualized production at all wind speeds at the sites.

        Further, while Dabiri is finding interesting improvements in VAWT net efficiency with arrays of them, this is with Darrieus-style VAWTs. Based on my understanding of the effect he is taking advantage of, I don’t see that it as likely to work with your Savonius-style helical turbine.

        I’m afraid I don’t see anything to suggest that your helical VAWT is that much different than others. It would be great for pumping water in a place where aesthetics mattered, such as rural estates and gardens, but I don’t see it being useful for generating electricity in any useful amounts at a good LCOE.

        I don’t believe that your solution is at all competitive with Bergy’s.

        My apologies for not being more positive.

  4. Bryan · · Reply

    I’ve been making small VAWTs for a number of years now and I agree with your analysis. One additional “advantage” of the VAWT you might want to address is the possibility of locating the generator at ground level. I don’t know why it is assumed that the VAWT would be located near the ground, it seems to me it could be placed on a tower. If that is so, a shaft could be run to a generator at the base of the tower. My understanding is that HAWT gearboxes do break down and it is expensive to pluck them out of the nacelle.

    1. Safer maintenance would also help against a favorite “more humans killed by wind than nuclear” argument, though Fukushima might make that obsolete due to bioaccumulation in migratory fish.

      1. Nuclear and wind energy are both equally low risk statistically and historically for humans. The pro-nuclear math ignores construction deaths for nuclear and includes non-utility scale wind accidents and people hanging themselves from wind turbines, for example, so the sample sets aren’t equal.

        My problem with nuclear as a strategy is with things almost entirely unrelated to safety or the technology. Social and economic factors make it low viability. I can’t link my post on wind being more pragmatic than nuclear from my mobile device but have a look in the index for it and comment further there.

  5. […] Links Quick Overview VAWT v. HAWT COMPARISON (PDF) Are VAWTs better? Why aren’t VAWTs more popuar? […]

  6. Sandro · · Reply

    re:VAWT vs. HAWT given Dabiri’s calculation: what you’re missing Mike, is that the cost of the HAWT is significantly greater, and requires significantly more technical infrastructure to build and maintain for the same price point.

    Developing nations don’t deploy renewables because of the lack of expertise, locally sourced materials of sufficient quality for the large towers, and the subsequent costs needed to meet the necessary requirements. Dabiri’s VAWT costs change this picture significantly.

    Analogously, while the western world can rely on better materials and more widespread expertise, VAWTs can still be deployed where HAWTs cannot.

    Furthermore, while the VAWTs are spaced much more closely, that doesn’t necessarily preclude all other uses, just certain other uses. Also, the HAWT’s actual footprint should also account for the roads needed to access them, roads which might otherwise not exist or be used for other purposes.

    The more compact VAWT array seems to make them more amenable to deployment in urban environments as well, where the actual load is, which seems like a critical application for which HAWTs are ill-suited.

    1. Hi Sandro . . .

      I’m afraid you are incorrect in most of your points.

      Equivalently scaled HAWTs are cheaper than equivalently scaled VAWTs, even at small scale. They use less material to sweep the same area and generate the same electricity. And their LCOE as a result is better. That’s why four of the five top selling small wind generators are HAWTs, and the fifth is attractive and part of a line of energy solutions from an intelligent company. http://planetsave.com/2013/05/21/top-five-small-wind-turbines-in-sales/

      Regarding developing nations, they are just like any other country. They are best served by the least expensive form of wind generation on a per KWh basis. HAWTs exist at every scale. There are very, very few places where VAWTs can generate electricity where HAWTs don’t generate electricity cheaper. Perhaps we are thinking of different developing nations, but utility scale wind energy is in over 100 nations today, which incorporates a lot of what are traditionally thought of as developing nations. And that wind generation is almost 100% in the form of HAWTs. If you are talking about impoverished nations with subsistence farming, I completely agree that extremely simple Savonious-style turbines built out of local scrap material are excellent for pumping water.

      Dabiri’s VAWT arrays are spaced at 1.65 diameters apart. Between the bases and the narrow paths, the cabling and the concentrating electrical infrastructure, there isn’t room for any other use for the land they sit on. It’s 100% usage. That’s really hard to debate, so I’m unclear why you are trying.

      As for HAWT footprint, the 1-2% does include access roads and secondary equipment as well as the turbine bases themselves.

      You are kind of correct that VAWTs are slightly more suitable for some urban settings, like downtown rooftops. But it’s worth looking at real urban wind generation on this page maintained by Paul Gipe. http://www.wind-works.org/cms/index.php?id=540

      VAWTs are nice for some niche uses. And they can be pretty. And Dabiri is extending their niche a bit, which is great. But there are 250,000 utility-scale HAWTs generating electricity today for a reason.

      1. I agree with many of your points Mike, though I think you are missing the forest for the trees, or perhaps mistaking the tools of experiment as the way a solution must be implemented. The truly interesting experiment here is you! Seeing if an expert such as yourself who has confidently pronounced a truth can allow that there may be more to consider than they had first thought. That may be more interesting than your opinion to me. Rarely have I seen someone like yourself, as confident as you have come out, be willing to truly consider another perspective.

        I have seen nothing in Dabiri’s work, using the cut down to 1m dia x 10m tall, Windspires (that Dabiri himself calls eco-bling in his presentation to the Moore foundation), that indicates Dabiri believes that final arrays would use such a small turbine or even this particular geometry. Like you I have corresponded with him, and I understand he is working on something else, still a low solidity VAWT, but not exactly this one. Like you as well he seems enamoured with high tech materials, and processes, so his work reflects that, looking at using carbon fibre etc, to increase strength to weight. Regardless Dabiri’s experimental work of the last few years is not meant to show the size of turbines that would be used in a final array, it’s meant to show that VAWT’s interact differently than HAWT’s and can in fact have a neutral, or even slightly positive interaction when closely spaced, unlike the HAWT counter part. He’s merely making use of what’s commonly available to check and prove his intuition, which it turns out was correct. If in the future this system were to be commercially deployed, they would undoubtably be much larger, though not likely as large as the MW HAWT. If the instead of 30 ft, were 60ft, the spacing between them would permit all kinds of uses (as in fact the spacing of the smaller ones in the experiment would), and since the most common use of wind farm land is farming, then I think it would be fair to say that the land use, just as in a MW HAWT installation, would be neutral. The difference is that the same amount of land that is used in the MW HAWT array, would produce many more Watts if used in a tight VAWT array. As I said earlier and to which you seem to agree, the real question is not as much watts per acre, but watts per dollar of installed cost. This is where my work is more interesting, and I believe your overly quick review of my turbine, has allowed you to miss some key issues. Firstly when you consider a MW Hawt, it must be recognized that the live span of the blades, and many of the components have very finite lives. The components are very highly stressed, and yet must be designed with a maximal strength to weight, and maximum stiffness. They are beautifully engineered, and manufactured like aerospace components, and make use of high purity materials in clean room like facilities. So while compared to a high solidity VAWT like mine, they use a small amount of material to sweep a very large area, the cost for doing so is high, and the lifetime limited. In comparison, like a snail shell or egg, my turbine uses self reinforcing continuous arches, 3D curves, which mean that rather than having to build in beams to resist the enormous cantilevering forces, the skin of the turbine itself becomes it’s own supporting arch. With my turbine rotating around a stationary tower, on a vertical axis, there is no significant cantilevering force to cause stress. This allows a whole range of manufacturing materials and processes to be used, which MAY bring the costs per area down below that of MW HAWT. Of course, the MW HAWT has access to a superior wind resource, being located hundreds of feet in the air, but is that always true? And at the cost of how much concrete and steel? Most CFD studies show that winds accelerate up slopes, cutting the wind shear level down almost to the ground itself. The wind resource is only simple on the prairies and ocean, in most of the world topography makes a big difference. For MW HAWT, which requires a completely uniform wind, with minimal turbulence, that difference is more likely to be destructive that beneficial, but that is not true of all turbines, the ART Turbine in particular seems to thrive in high turbulence environments. That’s all I have time for tonight, and perhaps all I will take the time for, as in my experience, it’s unlikely someone as sure of themselves as you seem to be, will be willing to accept that in a rush to judgment, perhaps they missed some things, and reconsider their position. I’m saying that you are correct, MW HAWT are a good solution, proven and working in many instances, and they need advocates like you. I’m also saying that you are an expert in what is, and experts are by definition people who know more and more about less and less. When you rush to judge all systems that have a resemblance to something you know (in my case turbines like helix, or Venger), you do yourself a disservice, and a disservice to the people you are claiming to be trying to help as while a ford escort may resemble a race car, it is far from it. Goodnite Mike, and thank you for your patience, as I know I can be long winded.

      2. I’m with Paul Gipe on this kind of thing. If you think you have something better, all you have to do is prove it. Build it, have it independently tested by people who use a valid method and valid forms of calculations of output. Do full lifecycle cost of electricity workups per ISO. Sell it.

        Once again, you have an attractive, low efficiency Savonius-style turbine. It probably has a decent niche for low volume sales.

        Good luck and take care.

      3. Hi Mike,

        Perhaps the best small HAWT for sale, the 10kW Bergy, as rated by Small Wind Certification Counsel, has a max Cp of .31, so while MW HAWT may have efficiencies of almost .5, there is no manufacturer claiming this in small wind HAWT’s.

        Are you? If so on what basis?

        The ART Turbine, in testing under the supervision of Mechanical Engineer Jon Scott (as he reports in the letter on my website), found that the ART Turbine had a max measured Cp of .29, with a probability that because of our test equipment, it may have peaked a bit above that. Engineer and grad student Matt Hall, in a thorough review of the test data produced by Jon and I, found a max Cp of .31, and also noted that the turbine may have been able to exceed this. There is no reason for you to characterize the ART Turbine as low efficiency that I can see. On what basis do you conclude it’s low efficiency?

        Seems like you have jumped to a conclusion?

        At 11:03 you note that you haven’t heard of my turbine before, at 13:10 you respond to another comment, and at 14:44 you respond to me that my turbine is low efficiency. That seems to be a very short time to look at any data.

        The real question here is not about my turbine, it’s about your willingness to do what you say you do, provide information and context.

        Clearly you understand fairly well MW HAWT, but you seem unaware that for various reasons kW HAWT is not equivalent in performance to MW.

        Some of the reasons that kW and MW HAWT have differences in performance are related to Reynolds numbers, which as a wind turbine Guru, I am sure you are familiar with. This explains why a wing with a foil depth of 6″ is going to have a much lower L/D than one of 60″ and therefore it is easy to see why a small low solidity HAWT, or VAWT is going to have lower performance than the exact same system scaled up.

        This is very exciting, as right now my 1.85 sq meter VAWT(the version tested by Jon), is showing a comparable Cp to a 41 sq m HAWT.

        A reasonable question about this is at what Reynolds number will the ART Turbine reach it’s sweet spot? For MW HAWT, as for jumbo jets, it’s clear the sweet spot is well above 10ft of blade depth.

        Anyway it’s an interesting discussion. I hope you’ll join in. Best Wishes, Drew

      4. My apologies Drew but as I read the assessment written by Mr Scott this was only at winds above 10 m/s which is not as I understand it the standard methodology for calculating this factor. It says this in the first paragraph.

        I read your provided information from your website and found something that strongly suggests misunderstanding of how turbines are rated and compared. Perhaps I’m in error. I’ll do a bit more research than I already did to confirm my understanding. Triple check instead of the double checking I already did.

        A reasonable question is why you think you’ve done what no inventor of a helical VAWT in decades has done.

      5. Why do I think I’ve done what no inventor of a helical VAWT has done?, My thinking is based on evidence, first and most simply, that observably, my turbine turns faster than the wind, unloaded almost 50% faster, there is no other High Solidity VAWT that does this that I have ever heard of. From the Blackwell report you will see that they claimed to have an optimized Savonius that turned at 1.1 x wind speed, but in fact as is shown in the report https://etd.ohiolink.edu/ap:0:0:APPLICATION_PROCESS%3DDOWNLOAD_ETD_SUB_DOC_ACCNUM:::F1501_ID:dayton1271306622%2Cinline , by Ian Ross an unloaded Savonius is limited to .5x wind speed unloaded, optimally loaded it is only .3. That is the easiest to measure metric, that shows my turbine is substantially different from other high solidity turbines.

        The next big issue to grasp is aerodynamic scaling, and on this I was educated by Dr. Curran Crawford, Phd from MIT among others. Curran’s thesis was on aerodynamic modelling of HAWT turbines. This may address something that’s bothering you to do with my testing.

        When you have a wind turbine, or airplane you wish to study in reduced scale, how do you apply the findings to a full scale unit.

        What is done, is that if you use a 1/2 scale model, then in the wind tunnel, you run 200% speed, and then your L/D metrics will be correct for the full scale model at 100% speed.

        I’m not sure if that’s clear, so to use the example of my 8ft turbine, which at 1.85 sq m swept area is too small to be useful is really a 50% model of a 16ft turbine.

        What that means is that the Cp, and TSR measurements at 80km/hr in the 8ft turbine, translates in a 16ft turbine to the Cp and TSR that will occur at 40km/hr.

        This is one of the reasons that MW turbines are being designed larger and larger, because not only do they sweep more area as they get larger, but more energy is collected from each unit of area swept, at lower wind speeds, do to the scaling.

        In my page http://artturbine.com/understanding-solidity/ that confirms the data we have, showing that if a MW turbine with a 3m deep foil is attaining a .5 Cp, then a kW turbine with a .5 M deep foils should have a max Cp of .28 (almost exactly what the Skystream does).

        I think the larger question is not why do I think I’ve done something new, but how did I come up with it. That’s a long story, but in short form, like most good inventions, it was a byproduct of research in another direction. I was not convinced that I could reach high efficiency, but I was curious if I could figure out a way of building low efficiency Savonius type turbines very inexpensively. I did of course want to get as much efficiency out of them as possible, and so I read widely, especially the work of Dr’s Benesh, Modi and Fernando. They convinced me that Savonius turbines were mischaracterized and not properly understood. And I kept working on ways to both balance out the high torque pulsation characteristic of conventional Savonius, using the well known method of making them helical, but also trying to find ways both in prototyping, and in production of keeping costs down. In the end, reading a lot of papers, including the very interesting CFD work of Rahai, I came to some breakthrough realizations, that lead me to this shape.

        Thanks for your interest, I hope this hasn’t bored you too much.
        Best Wishes,

      6. My recommendation, perhaps one you are already acting on, is to get your device tested independently, by a reputable and known wind energy testing facility. Sandia or the PEI facility come to mind. And, of course, to have your device certified. Then to move forward with a full LCA per ISO standards.

        I look forward to seeing the results.

      7. Thanks Mike, we are in agreement, that it’s time to get more independent testing done, and yes, it is one of the things I’m working on.

        It’s a bit chicken and egg though, as testing isn’t free. The Canadian wind testing centre is likely who we will go with http://www.weican.ca however we’ve been told that it will cost 80,000.00$ or more, not including the turbine, and delivery of the turbine. Not an insignificant amount of money. Further, the testing they do is oriented toward certification of a commercial product. If we supply them with a prototype, then make any changes (alternator, structure, shape) when we move to manufacturing, the certification won’t apply to the new turbine. The way I’ve been making prototypes is to computer draw, make templates, cut from styrene foam, and hand finish to shape then coat, with epoxy and glass, or urethane. On a production basis, they would be made very differently than this of course.

        It’s not an insurmountable problem, and one that I am working on.

        I think though two significant things that should be recognized as being different in the ART Turbine business, compared to other companies.

        First, we have real engineers, willing to go on record saying they were involved in testing, or reviewing data and this is what they saw. This is unheard of for a wind tech startup, UGE claims to have sold 100’s to 1000’s of systems and they don’t do this. In fact UGE applied to enter the SWCC certification program in 2010, according to the SWCC


        they then made claims that they were “in process” to be certified, but didn’t start collecting or submitting data until 2012 and 2013 (after selling many turbines, and more “distributorships”). Now they have had one turbine under test for a year, after selling turbines for almost 4, and they still haven’t certified or had a qualified engineer state “this is what I saw under these conditions).

        This is a pattern similar to the failed Helix, where turbine capacity was overstated very significantly, promises were made to have independent review, when the data finally was collected, Helix failed. In the case of vertical low solidity, with the poor Reynolds # available in a shallow blade, it’s unlikely that UGE can meet their claimed Cp.27 at 12m/s (this was calculated by Jon Scott, using the claimed output of the UGE turbine).

        Windspire, the VAWT used by Dabiri (though Dabiri shortens them), was tested by NREL labs, and found to have a max Cp of .17.

        Second, ART Turbine has not been selling turbines, we have waited until we have been confident enough in our testing to make public pronouncements, and we have been willing to submit our data to outside review. Though my life could have been made much simpler by getting cash-flow positive, I have chosen to take the higher, and more difficult road.

        I say all this because I want it to be recognized that both the ART Turbine is different (high solidity vertical axis that has an optimal TSR of 1+), and that the way ART Turbine is doing business is different.

        I don’t need you to believe that it’s economic. With the information you have, you couldn’t know either way right now.

        I believe that given the history that small VAWT technology has, it needs some skeptical enquirers like yourself.

        It’s also important that the baby not be thrown out with the bathwater. Once again, thanks for your patience, I can be a bit bristly, but it’s not my intention to be.

      8. I’m reasonably sure UGE overstates their claims, but they also don’t claim to be replacements for utility-scale HAWTS, and they sell their aesthetically pleasing VAWTs as part of a collection of power solutions for small businesses, homes and remote comms towers. They aren’t making particularly egregious claims for their wind generation, and are targeting niches where it makes sense as part of a portfolio of solutions. They are in the top five selling small wind turbines because of marketing and business model, as well as an adequately pleasant looking device that avoids the stigma of HAWTs where that exists in buyers’ minds.

        And it’s hard to say UGE built anything unique or intended to; I’ve certainly not seen anything from them making extraordinary claims (I haven’t read everything however). Spiral blade Darrieus-style devices preceded UGE and are still being invented. They seem to have seen a market niche or three that were under serviced and targeted solutions at them. It’s a business, not a technical revolution.

        The difference between marketing hype and extraordinary engineering claims is an interesting one.

  7. Jon Scott · · Reply

    Hi Mike,

    Re Dabiri VAWT arrays vs large HAWTs

    I have read all the comments here, as well as the ones regarding the Dabiri article, and there is an important concept that needs to be brought up. That issue is the cost of a large number of “small” VAWTs vs the cost of a large HAWT.

    Dr Dabiri stated that the results from his current 18 or 24 VAWT array support the results he was getting a few years ago from the 6 VAWT array, so if we assume that the VAWT array concept works, then the next question is what does it cost to commission a farm of say 5,000 to 15,000 VAWTs compared to a farm of 10 large HAWTs ? Consider that a large HAWT is a very complicated device with a large number of moving parts, and smaller VAWTs have only one moving part each, and further considering that the HAWT needs a large crane for installation, but the HAWTs can be installed using small equipment. So, if the VAWT farm can produce five to ten times as much energy as a similar size farm of HAWTs, does the VAWT farm cost less than five to ten times as much ?

    To say this in a different way: Assuming that VAWTs are less efficient per swept area than HAWTs, it doesn’t matter, if the cost difference compensates.

    In Dr Dabiri’s presentation to the Moore Foundation, he even has a slide showing an automated car factory to suggest that VAWTs need to be produced at those volumes to allow the economics that can make VAWT farms superior to HAWT farms.

    So, to me, it boils down to a costing + efficiency exercise, rather than just an efficiency (Cp) comparison. And furthermore, Dr Dabiri’s work from a few years ago was with low efficiency (Cp = 0.17) Windspires, The ART Turbine has a much higher efficiency (Cp = 0.29). So, the prognosis for VAWT farms is likely even better than Dr Dabiri suggests.

    I have done costing analyses comparing VAWT farms to HAWT farms, based on producing and installing the VAWTs in large quantities (I am a mechanical engineer specializing in product development), and it looks to be extremely cost effective, but someone more familiar with the industry should review them to confirm the results.

    One more comment: Wind farms using larger VAWTs would have even better efficiencies, but there will be a size “sweet spot” where it does not make sense to make them any larger.

    Jon Scott, P.Eng

    1. The VAWT farm can’t provide 5-10 times the energy of a HAWT farm unless you accept the erroneous assumption of 100% land coverage for HAWTs. That’s the first challenge with your comments. Dabiri’s research is finding interesting results that extend the overall effectiveness of VAWTs, but in that part he’s vastly overstating his findings. I’ve had an extended conversation with him on this point and assume that in future his innate intellectual and academic honesty will require him to substantially alter this claim. And land use is a contributing economic factor, not a deciding factor. 10000-15000 VAWTs take all of the land that they are on out of useful production, while 10 HAWTs allow farming and other uses up to their bases. Depending on the alternative uses of the land, this can be a major factor or a minor factor, but Watts per square meter isn’t a metric that is used by anyone as deciding factor in energy generation decisions.

      Dabiri’s approach, as he admits, requires building a much simpler VAWT which doesn’t exist today, creating an entire manufacturing and supply chain which doesn’t exist today and an entire logistical network which doesn’t exist today. These aren’t insurmountable, but frankly that will take a couple of decades to reach critical mass, and only if very clear-headed projections indicate that it will be economic. With the rapidly dropping price of HAWTs, it’s unclear why anyone would make that bet. Dabiri’s approach would have to be significantly better and cheaper than HAWTs — and my analysis indicates that it isn’t — in order for any market movement to occur.

      Regaring Windspire vs ART efficiency, you’ll forgive me if I take your numbers with a grain of salt. Darrieus vs Savonius efficiency ratios have been well understood for decades. Helical VAWTs are common. The evidence presented so far doesn’t make it clear that an apples-to-apples calculation comparison for the ART has been made. I simply don’t trust the extraordinary claims being made, and have suggested independent testing. I assume that you are the Jon Scott who did some calculations and assessments around the ART? It would be helpful to understand your methodology and compare it to the methodology used for calculating effectiveness of other wind energy devices.

      An additional challenges related to the ART is that there is no evidence that Dabiri’s insight, based on schooling fish and counter-rotating Darrieus-style turbines, would be applicable to an array of Savonius VAWTs, whether helical or not. Making a claim that the allegedly more efficient ART could be dropped into a Dabiri-array just isn’t credible either.

      Dabiri’s results are interesting and extending VAWT effectiveness which certainly makes them viable in more niches.

      Where we agree is on cost of building, shipping and installing. At present I see no evidence that the complicated shape of the ART would be cheaper to mass produce in any robust form than other VAWTs (which never achieved mass production in any event). I’ve spent enough learning about industrial engineering, materials science and manufacturing processes to be leery of that until I’ve seen a pretty solid LCA based on ISO methodologies. At present, the ART is a handmade prototype that’s a long way from a production prototype.

      You might be interested in the Innwind project (http://www.innwind.eu), which is aiming to solve the engineering challenges related to 20 MW HAWTs just as the Upwind project solved them for 10 MW HAWTs. HAWT innovation is far from tapped out, and it exists within the context of a massive international manufacturing and supply chain that exists today.

      I think there’s a lot higher probability of HAWTs continuing to be the dominant form of wind generation for the foreseeable future than any other form of wind generation. And I want to displace CO2 today, not maybe displace some tomorrow.

    2. Jon Scott · · Reply

      Hi Mike,

      Thanks for your quick reply to my post. Yes I am the Jon Scott that tested the ART Turbine, and yes the small one (approx 2 sq.m.) does have a Cp of 0.288 at 11 m/s (Cp = 0.220 @ 5 m/s and Cp = 0.255 @ 8 m/s), and, It was tested in open air (no wind tunnel false results) with redundancy in the air speed measurement. But, the Cp is not as important as the combination of Cp and cost. Even though the ART Turbine is quite efficient, it also can be manufactured at low cost in high volume, since it is basically a piece of foam with a skin.

      Regarding the land use issue: It is true that a VAWT farm will use more of the available land than a HAWT farm, but I am assuming the land cost is very low. In the analysis I referred to, the land value was not considered. But, even if you assume that in a VAWT farm that 50% the land is used for the VAWTs, and in a HAWT farm that 2% of the land is used for the HAWTs, it will only matter if the land is very valuable. You yourself said that the land rental is a small factor in the economics.

      You brought up a very good point about the fact that HAWT development is happening now, and that the VAWT development would be in the future, maybe not decades away, but certainly years away.

      Jon Scott, P.Eng

      1. Please correct me if I am wrong, but lets look at some of the assumptions here.

        Assumption by Mike, the footprint of a MW HAWT is the base of the tower. Or does it include the shadow area of the blade? Or does it in include the whole “umbrella area” that the blades may pass over if the nacelle rotated 360deg?

        Clearly this depends on the land use, if the land is agricultural, and infrequently traveled by people, then the land occupied is really just the tower base, and perhaps, given that a MW turbine requires big service vehicles for installation, then perhaps access roads. It will be agreed I think that the issue of liability precedes MW HAWT from being within at least a rotor dia or two of human habitation or highways.

        In this instance, in farmland, removed from it’s primary use of farming is very small by a HAWT array, Mikes # is 1 or 2%. I think that’s reasonable.

        In a VAWT array, the size of the VAWT makes a big difference. If it’s an array of 1 kW turbines to make 1MW you are going to need 1000, turbines. If your VAWT is 10 kW you only need 100 turbines. The reality that an array of VAWT’s has a different class of liability should also be factored in. You will never see a HAWT of any substantial size, certainly not MW in a city, because they can shed blocks of ice that are big enough to be a hazard. Not an issue on farmland, but means they can’t be to close to highways or buildings. The constraints for MW HAWT, and kW VAWT are very different. The rotors used by Dabiri have frequently installed on buildings, and in public centres.

        In Dabiri’s report he used pairs of small rotors spaced very close together, with the pairs being 8 rotor dia apart. If your rotor is 1kW and 1m dia, that leaves 8m between rows, a road way allowance is generally 10m, so if you needed a road to access these turbines, 100% of the land would be occupied, and Mikes thesis would be correct.

        However these turbines are so small they are installed by Dabiri’s students by hand, so no road is needed, so the land removed from farming is very small, though likely greater than the MW HAWT and Mikes thesis is still incorrect, given that you don’t need permanent roads to access the turbines.

        In the case of a 10kW VAWT, say 4m dia, you get 80m spacing between pairs, and again if you need permanent roads for big cranes, then you “use up” quite a bit of land, compared to MW HAWT, however if you use 4m dia turbines that can be installed by rough duty service trucks and small off road cranes, again, you don’t need the roads, so any land taken out of use by the VAWT array is in the same order of magnitude as the HAWT array, however because the VAWT array isn’t towering 100 m in the air, you can install more turbines, closer to roads and buildings, so available W per acre of land may be much higher than with MW HAWT, even without the turbine density shown possible by Dabiri. This is especially true in constrained installations, where the VAWT array can be “fit” to the landscape, coming closer to roads, and edges of the install area.

        It’s all about your preconditions, Mike as an advocate for MW HAWT, which he is quick to point out is here now, and not a future “dream” seems to want to set preconditions that make MW HAWT look good, and anything else look impossible. As the expression goes “when your only tool is a hammer, every problem looks like a nail”. Calling Dabiri intellectually dishonest for not retracting his work seems over the top given the rules for this blog, but since Mikes the policeman for it, it’s up to him to make that call.

        For myself, I believe there is room for discovery in the world, and unlike Mike, I am not so sure of what’s possible, and what’s not and so I don’t rush to judge till I prove it. That’s what makes it possible for me to create.

        Though my performance evidence certainly doesn’t seem to be to Mikes standard, it’s good enough for a very experienced engineer like Jon, (who I’m very fortunate to have worked with), then at this stage of my business, it’s good enough for me. Now the larger question, which as Mike and I have agreed upon from the beginning I think, is $ to W, and then $ to Whr/year, including a LCA, to see if we can show that the lifespan of kW VAWT is substantially greater than MW HAWT.

        Thanks once again Mike for being open to dialog and sharing your opinions with us.

      2. Unfortunately, your assumptions are incorrect. Dabiri spaces his turbines 1.65 rotor diameters apart, not 8 diameters. You might be mistaking HAWT spacing of 10 diameters downwind and 4-6 diameters cross wind.


        I’m afraid your argument in regard to land use isn’t accurate.

        As for urban wind generation, I point you at Paul Gipe’s page on this to see what substantive wind generation in urban areas looks like. http://www.wind-works.org/cms/index.php?id=540

        I agree completely that VAWTs can be put on buildings and bridges in urban areas for trivial amounts of generation. That’s irrelevant to utility-scale generation and Dabiri’s work.

        Good luck with further testing and certification of your device.

      3. 8 dia rotor spacing between rotor pairs can be seen here


        Slide 10

        It is 1.65 spacing in turbine pairs, and 8dia between pairs, as I pointed out, no assumption needed.

        My argument re land use stands until corrected as far as I’m concerned. You can disagree in general, as you have, or be specific if you’d like. I’d prefer to hear your argument.

        I’m not that concerned with urban wind generation, that’s the business of your friends URBAN Green Energy, who until they release a report from an engineer, or certify a result, deserve extreme scepticism in my opinion.

        UGE must have at least a dozen engineers working for them, they’ve been collecting data for years after selling 100’s to 1000’s of turbines at least of turbines. Why wouldn’t they release a report from an engineer? Why apply for certification in 2010, and only start collecting data to certify in 2012 and 2013?

        Sounds fishy to me, I’m frankly stunned that you would refer to them in any positive sense. I represent a startup that’s not even selling turbines yet, and I’ve released a 1000 x the data that UGE has.

        My perspective on helical low solidity VAWT’s is pretty informed. I’ve read many papers, including all of Gorlov’s work. The work done by Verdant on the Gorlov design (flunked) and
        I had access to a company that licensed the Gorlov design (first helical Darius, patented, no prior art, no one disputed the patent, published 1996 I think).

        Gorlov claimed .35 Cp and self starting since then others have reviewed his data and not found support for Gorlov’s numbers.

        The company who granted me access to their data bought 4 turbines from Gorlov for use in Kinetic hydro. 1m dia 2m tall. The best they could get in water (so closer to ideal Reynolds numbers then in air, you can think of this like testing a huge greater than 1m deep foil) was Cp .19, and using the same size Darius H rotor, were able to get .24 but only at pretty extreme speeds. Both turbines (Gorlov and Darius) were fragile and failed in testing.

        Gorlov has quite paying his patent fee’s because no one has been able to make them produce electricity economically, or last.

        I have seen first Turby, then QR, and now UGE all producing the Gorlov, none of them with the honesty to give him credit. None have been able to produce an engineer who will put their name on a report… As I said, I’m very very surprised a skeptic like you has bought their glossy ad copy.

      4. Fascinating, and thanks for bringing that to my attention. 8 rotor diameters for any significantly scaled VAWT array rapidly approaches HAWT spacing with an inherently less efficient generation device in a poorer wind resource height. Once again, I’m left underwhelmed.

        I’m interested in apples-to-apples comparisons. They appear to be short on the ground. I’ll continue to watch Dabiri’s results of course.

        And you are getting bristly again. As I said earlier, I put a different weight on marketing vs engineering claims. I respect UGE for understanding the business niche they are targeting and not claiming to be replacing utility scale generation, not because their technology is superior.

        My general guidance to anyone trying to innovate in the field of wind energy is to start from the business niche and business model, then fit an OEM device to the target requirements. You, like many others, chose to come at it from the other direction. That’s your prerogative of course, but there is a remarkable amount of wasted investment dollars in reinventing the wind turbine.

        I’ll apologize in advance for not wishing to spend too much more time discussing hypotheticals. My primary goal is to remove blockers from construction of something that exists today and can do some good. The reason I maintain assessments of VAWTs and other technologies is to debunk myths that they are better and HAWTs shouldn’t be built as a result.

        Once again, I look forward to independent assessment by a qualified test facility. As we’ve agreed, full lifecycle costs per watts is critical.

      5. The geometry of a VAWT array, especially as used by Dabiri results in much greater swept area per acre than a MW HAWT array, even if both the HAWT’s and VAWTs are at 4 dia spacing in all directions. This is counter intuitive and so I understand your misconception.

        A HAWT swept are is directly related to it’s dia, (pie R squared) (1x dia HAWT yields .78 swept area)

        A cylindrical VAWT is its dia x height. (1x dia x 4 dia height yields 4x swept area)

        In Dabiri’s case 1 dia x4 dia tall.

        So two arrays 1 VAWT with 1 HAWT, with identical dia turbines spaced 4 rotor dia apart (because Dabiri is using sets of 2 rotors spaced 8 dia),

        would leave the HAWT array 1x swept area

        whereas the VAWT array would have slightly greater than 5X swept area per land area. The VAWT array also has the benefit of being able to conform to the available land area, using edges and being closer to roads or habitation. This could also be a substantial difference.

        This calculation for simplicity uses 4 dia spacing in all directions. I think we are in agreement that this is not suitable for HAWT arrays, they require 10 dia downwind spacing, in this calculation this means that we are overstating the case for the HAWT array by just over 2x. A more realistic calculation would give greater than 12x swept area per land area, VAWT vs HAWT.

        I agree that in the prairie, or other flat topography, the hub height difference would make a substantial difference to energy input to the array.

        In mountainous or hilly regions, it isn’t so clear cut.

        There were many experts who called the telephone a novelty compared to the telegraph, and wasn’t it Bill Gates who said something about how no personal computer would need more than 64K of memory. People with their attentions focused on a singular goal can often miss the forest for the trees. Just look at the more recent pronouncement from Microsofts CEO, that no one will want a tablet without a real keyboard and mouse.

        I thank you for your interesting review of the variable amplitude sound, and it’s very useful findings showing the low frequency of occurrence in the UK. I agree, it seems that the low frequency of occurrence shown in the study, makes it seem that sound concerns in MW HAWT are overstated.

  8. As an Architect, I prefer to have what is referred to as the Vertical axis turbine (not just one-multiple) mounted on a horizontal shaft mounted on 2 supports. This will prevent any wobbling and subsequently, vibration and noise production too!

  9. Frank Israel · · Reply

    Perhaps the following would be helpful to this very informative discussion:

    1. Thanks. For those uninterested in reading Dabiri’s underlying papers as I did when writing about him initially this will give a good introduction.

  10. Loren Webb · · Reply

    What I found through testing was by gathering wind energy from a sail or damn as more discriptive and feed the rotor only on the power side, will more than double the amount of torque produced from the rotor. Have a few pictures of what I built. Would love to have better testing to prove the wind pressure build up transfers directly into the rotor. By gathering from a surface area at least ten times larger than your rotor blade your interacting with a much larger volume of wind.

    1. This is a well understood principle. The Venturi Effect and related effects have been observed and understood for centuries.

      What is also well understood is that creation of massive structures to accelerate wind energy past a smaller wind turbine is never cost effective compared to just putting a bigger wind turbine in clean air.

      There are turbines that are placed in geographical locations which take advantage of this effect such as ridge tops, valley mouths and the foothills of mountain ranges. This is taking advantage of geographical improvement of the wind resource however, not building unnecessary elements into the wind generator itself.

  11. […] of the persistent myths of wind energy is that vertical axis wind turbines (VAWTs) are better than the iconic three-bladed […]

  12. […] of the persistent myths of wind energy is that vertical axis wind turbines (VAWTs) are better than the iconic three-bladed […]

  13. Rajesh Dommeti · · Reply

    it is good to see that over all discussion … as an electrical engineer my intention is to know “how far the generators used that to variable speed are suitable for VWATs(interms of efficiency and mechanical stress compared to Hwat) and also any one attempted Axial flux machine configuration, that are much more advantages than conventional generator for Low and medium power. thanx to author

  14. […] and cooking are from oil and electricity comes from a generator and a wind turbine, supplying the biggest set of batteries you have ever […]

  15. Greetings one and all, and thank you, Mike, for your informative blog. After skimming through the comments posted, there seems to be a few important points overlooked concerning VAWT technology and its implementation. The first point concerns the fundamental aerodynamics of a VAWT’s airfoil having to cycle through an angle of attack of 360-degrees upon every rotation. This fact necessarily causes impulsive loading on the machine’s blade attachment points, torque tube, and power train. These cyclic loads are significant fatigue loads which must be factored into the design of a VAWT, which results in a heavier wind machine, or higher cost of energy per unit mass. The impulsive loading also adds significantly to the overall level of maintenance required during the life-cycle of a VAWT. The second point concerns the wind loading across the swept area of a VAWT’s rotor… the loading is asymmetric – not symmetric – which is increasingly important as the wind machine’s diameter exceeds ~6 meters – whether the machine is supported by guy-wires, or not, as the machine might be, if it were on top of a pole or tower. The third point echoes the historically higher OEM costs associated with the operation of a VAWT wind park when compared to a comparable HAWT installation. High OEM costs were one of the main factors in the demise of FloWind’s VAWT operation in the California wind fields.

  16. Good Morning Richard,

    I agree with many of your points as they apply to Darius type wind machines, and would add that a fundamental problem with Darius designs is that aerodynamic efficiency rises as the blades become longer and thinner (and therefor less rigid). This is examined in the Sandia labs retrospective paper quoted earlier in the discussion where they point out that the low solidity Darius FloWind blades faced an order of magnitude greater cyclic loading than airplane wings.

    What I have been working on is fundamentally different though. A high solidity VAWT, being rather than a number of long thin blades, a single large solid blade, as such inherently much stiffer, and as it rotates around it’s tower (which is inside the blade like a stub axle, on which there is no cantilevered loading. It’s lower speed, and large surface (constructed as a stressed skin), makes it orders of magnitude stiffer than the historic Darius turbines.

    As I’ve said, I agree with some of what you’ve said in regards to the structural problems faced by Darius turbines. In fact though the flow around (before, after, and through) a VAWT is much more complicated than you describe.

    All VAWT’s are not the same, but in general a VAWT, as does a flettner rotor, tends to wrap the wind around itself. If you go through the trouble and download a copy of NASA’s foilsim software, set the “foil” to a cylinder, and set the cylinder to rotate, you will see that a rotating cylinder in air will cause a major distortion in the flow, as much as 2 dia upwind and downwind (and latterly). This aligns well with the CFD work done by Dr. John Dabiri and his students, on low solidity Darius type VAWT’s, as well as others.

  17. Don Kornelson · · Reply

    That was an excellent article and you have outlined the up’s and downs of both technologies fairly well. I am an engineer having a fair amount of experience in this field but I am also a realist and everyone I have talked to likes cheap power from HAWT’s… just not in their back yard. In fact nobody wants to see them because unfortunately most would agree they are ugly which is a problem.
    Which is where I believe VAWT’s come into play and while the material technology and engineering skill is still lacking in this area the fact remains that people prefer VAWT technology if given a choice. Which is what were talking about isn’t it?, if the two technologies were comparable on there price point in $/Kw/hr we wouldn’t be having this debate.

    In any case we see very little progress in HAWT technology and at best it is barely incremental say 0.5 % here and there suffering from the same cost inefficiencies/ hare brained idea’s we see with VAWT’s. Personally I think the future lies with VAWT’s for various reasons, first they are pleasing to the eye on any scale and have many different variations. Second I think we can all agree they have room for a massive amount of improvement. Which relates to our future and if were not improving by leaps and bounds concerning the scale of problems we face then in actuality were falling behind. The norm is not an option at this point and bigger is not always better, better is better regardless of it’s scale.

    1. Actually your first assertion isn’t true. Most people like the look of HAWTS. Not sure what you’ve been reading but they have a strong majority who like the look of them. Have a look at these videos of people who live with them for example.

      In their own words: People living among and near wind farms on video | barnard on wind


      I agree that a reasonably large minority of people don’t want them in their backyards, on average. There are certainly hotspots where a majority don’t want them but that’s unusual.

      For small wind there are a reasonable number who want VAWTs because they are literally in their backyards and they want kinetic sculptures that produce electricity. But in small wind the vast, vast majority of devices sold are HAWTS.

      As for your assertion that HAWT technology isn’t advancing that’s completely wrong. They are procuring much more electricity, much more of the time with much lower reliability. Maybe in a slice of small wind they aren’t changing much but that’s because they are effective, but in big wind the transformation and innovation is continuous.

  18. ehsan · · Reply

    my question is that are betz limit apply for both vertical and horizontal wind turbines or not?

    1. In the scale of any given VAWT ever built, yes. In theory if you have one big enough with no central mast then the downwind blades can be considered to be working in separate clean air as airflow will come in from the top and sides. The scale of this is large however, requiring a radius of probably in the range of 100 meters minimum. Otherwise you are just dealing with the same energy bound into the same ‘packet’ of air.

  19. Tim · · Reply

    HAWT may be suitable for large scale energy generation, but there are environments where they are unsuitable.

    High wind, a HAWT will shut down at 25m/s, many VAWTs will keep generating in 50m/s, 70m/s. You cannot over-generalise, each technology has a niche! It’s just the commercial wind farms with HAWTs are a very large niche, i.e. mainstream tech!

    In high winds, it’s all about survivability in those extreme conditions, and how well they operate. If you have plenty of wind, a few percent efficiency loss is nothing, does not matter one bit!

    If however, you have limited wind and need to extract as much energy as possible, then HAWTs are essentially the only way to go.

    Will you talk about cost efficiencies if you live off-grid up a mountain with 100mph winds? In that situation, give me a VAWT any day.

  20. Loren Webb · · Reply

    I have an entirely new take on a VAWT using wind pressure instead of wind speed. The wind pressure is gathered like a sail would and is fed directly into the rotor.Interaction with the wind is greatly increased and so is the available power at the rotor. the stationary walls that direct the wind only to the power side and surround the rotor with 5 openings for any direction of wind. 3 blades on a HAWT only have a small contact area to extract power, the VAWT I have designed interacts with a larger volume in the same sized area to become more efficiant than a HAWT of the same scale. Doors could easily be made in the walls to close the rotor from storm damage and allow the pressure to pass through. My prototype has shown great performance potencial and would like to find help to move forward.

    1. I can see about six major problems with what you have described. It will generate much less electricity for the same swept area and use much more material to achieve this poorer performance. It has been tried before, and simple torque generators inside structures and outside were built by the Persians centuries ago for milling and pumping water. http://en.m.wikipedia.org/wiki/Panemone_windmill

      If you are enjoying tinkering, have fun, but don’t think for a minute that you are doing something new that will be more efficient.

      1. Loren Webb · ·

        Hi Mike, Thanks for your response, it was interesting but not on point. I live near Lansing, Michigan area, and would like my vaut tested or at least looked at. It would take one day and three people and my unit would be up and running, I tried at the local college, but it’s hard to find contacts, so here I am. The power of a sail to move a ship is undisputed, so applying a rotor to extract the power instead of pushing a 4,000 lb boat makes sence to me. I have some pictures of a partial skinned unit that has proved to me it works, but where can I go with it? Loren Webb

      2. Loren Webb · ·

        Hi Mike, I see my new wind devise is still not understood. I feel the need the need to start over with a better description. Forget hawts and vawts, because this is a damn. As wind pressure pushes against a sail it accumulates a higher pressure than the front side and pushes the boat. This devise gathers wind pressure and feeds one side of a turbine in the center. My protype is proof that this theory of wind pressure producing power works, I still have no one that seems interested. It’s scale would compare with a 5 ft hawt with one turbine blade equaling all three hawt blades in square inch surface area. The hawt blades catch only the passing wind, with the blade area the only traction to produce power. My devise accumulates wind pressure into the turbine blades with cup shaped walls that open up at least 10n times larger than the turbine blades. Using pascals law of pressure,when is is assembled properly, the wind pressure interacts with the turbine more power is produced. I have watched this happen and my no scientific calculation was twice the power. Would like to have it measured professionally. Loren Webb

      3. My apologies, but you are describing a Savonius drag turbine. It’s the least effective form of wind generation.

        Please understand that I’m not particularly interested in discussing obsolete tech. If you truly have something innovative, build a prototype and have it independently tested. Prove it in other words.

      4. Loren Webb · ·

        Hi Mike, I have built a prototype, I live in the Lansing, Mi area. I have tried contacting LCC and M.S.U with no response from phone numbers, How would I go about having the unit tested? Any suggestions? Loren Webb

      5. This page from the PEI wind energy testing facility is informative. http://www.weican.ca/projects/funding.php

        Arrange funding and wind testing sites will pay attention to you.

        And consider Sandia. The only new wind ‘innovation’ I consider particularly valid had their adaptive rotor technology tested by Sandia.

        But please note that new wind ‘innovations’ are a dime a dozen and everyone actually working in the field understands that horizontal axis three blade wind turbines are the best technology and that incremental innovation of that technology is the priority. That’s because ninety years of testing technologies has proved that. Expect continued and justified skepticism especially if you can’t describe your technology. A paper detailing your design with pictures of your device would be useful. Establishing baseline data yourself using standard methods would be good too.

  21. Tim · · Reply

    How big is the unit?

    There are some VAWT ideas that have been tested very thoroughly, but on a ship or boat, they get very heavy relative to the weight of a sail. In high winds such a top-heavy boat is likely to capsize more.

    You need to look at power output and weight and how the centre of gravity is affected.

    A sail is tapered to the top, such that the forces on the mast are more concentrated at the base, but sails can be furled and unfurled, typically by wrapping the sail around the boom, depending on how much wind.

    With a sail, there is so much power, and a mechanical device as big as a sail is not as efficient because of mechanical losses, and other efficiency losses.

    There are so many VAWTs and HAWTs on the market, so it is saturated, so you have to be very certain about why you are doing it. You have to look at the capital cost per kW output, and if you cannot compete on that basis, you should save your money.

    Wind turbines are easily scalable, so the HAWTs can now get up to 8MW, you just specify the power output you want.

    I suggest you think very carefully about what you are trying to do.

  22. nandu · · Reply

    i really liked your detailed view. looks like vawt are more suited to homes as a backup purpose. also vawt it seems can be made with less
    complicated manuf process. just making the blades seems like a daunting task for hawt. also hawt have one more drawback. when hawt blades are spinning rapidly any change in wind direction will cause a gyroscopic presesion effect. this might damage hawt much sooner. vawt seems to have advantages of easier process of manuf and do not have any gyro issues in changing wind direction – pls comment

    1. VAWTs are easier to make, true. But they use about four times the material and take twice the swept area to generate the same amount of electricity, so the LCOE sucks. Some people think they are prettier, but they have to be pretty well off to overlook the massive cost disadvantage.

      As for blade speed, that’s an advantage due to aerodynamic addition to generation force, and they are speed limited by pitch management to prevent them from spinning too fast. Small ones really won’t have a problem shifting with the wind, but where the wind is really turbulent it’s also typically weak as well. VAWTs can outperform HAWTS in very turbulent conditions, but that doesn’t mean that they generate enough electricity to be worthwhile.

      As for homes, they are almost always better off with solar panels.

  23. Kevin Kirchman · · Reply

    Hi, Mike,
    I haven’t read the rest of the comments, so be patient if you’ve dealt with my comments before.

    Firstly, you say “VAWT blades are rarely at an optimal angle to the wind or in clean air, so they can never be as efficient as a triblade HAWT and won’t generate more electricity”.

    To be fair, there is a pass of every VAWT blade in clean air, in air from a constant direction, the same as for an HAWT. So that part of your comment is not accurate.

    As for optimal angle, depending on the design, as their are many, because the resultant wind (the prevailing plus that due to rotation) direction is always changing for a VAWT, including those of varying pitch, one can get a pretty good optimization here, just as is the optimization of the HAWT resultant wind, which comes at a very high expense because it is fixed in the twist of the blade.

    So you are missing a real issue with cost of constant profile blades vs. the complex asymetric blades of an HAWT. It’s not just the cost of materials, but also the cost of fabrication that determines the overall competitive comparison. And academic theorizing about fabrication costs are not credible here, as they should only be ascertained from producers.

    Finally, it would only be fair if you mentioned that each VAWT blade passes through the wind twice, giving more opportunity to harvest wind energy. Granted, there is additional turbulence in the back pass, but it still adds energy overall.

    There are now VAWTs that are producing a very HAWT-competitive production compared to the Betz factor. It is also increasingly acknowledged in the literature that an HAWT and a VAWT have different Betz factors, because of the second pass, and the possibility of fluid flow up and down through the axis area before it meets the next pass. We are looking at 59.3% of total energy possible for an HAWT vs. 64% or higher of total energy for a VAWT. Thus it is theoretically possible to produce more with a VAWT.

    1. My apologies but you repeat what I say, proving it, but don’t understand it. And no, you are not getting the results you think you are. Please reread the material.

      If you think you actually are getting these extraordinary results, prove it with independent testing at a recognized lab. Publish your actual results signed off by an organization which knows what it is doing. You will be disappointed but wiser. And will hopefully stop making extraordinary claims.

      It’s possible Sequestra Power should stick to energy-to-gas, but it’s difficult to tell as your website is locked down and the external information on it is virtually non-existent.

      Your brief statements already triggered four red flags from this list. You should consider the impression you are making.


      If I were to read the tea leaves from what little information is available, you intend to make remote and marine devices which use wind and solar energy and some form of gas — either compressed or processed from readily available raw materials — to provide a useful energy source. I’d look at this information before you spend too much money in this space, especially with a VAWT. http://cleantechnica.com/2014/03/25/offshore-vertical-axis-wind-turbines-sinking-swimming/

      1. Kevin Kirchman · ·

        Mike, I think you are being defensive–you claim to be unbiased.

        I have not discussed our project in the least, to be honest. There is no mention of our “results”, so you are sounding a bit crazy here.
        And our website is not “locked down”. It simply is not up, and never has been. If what we are doing was ready to be announced like the latest iPhone, then the product would already be ready to ship, which it is not. You’re not bright in that regard, and rather negative, to be honest.

        You say I have made extraordinary claims. I have made none. I actually was referring to a turbine manufacturer’s claims, completely unrelated to my firm, but that is another discussion. I was only suggesting you look harder out there.

        You have accused me of repeating what you were saying, but ignored new points I made. Again, you are simply incorrect to say “VAWT blades are rarely… in clean air”, and neither do you acknowledge their second pass.

        Your reference link on offshore VAWTs is already behind the times. Vertiwind, which it mentions twice without realizing it, is working with Technip, a fine energy engineering firm with 40,000 employees globally. Vertiwind now has their 2MW VAWT prototype up on land, and yes, they are behind schedule, but you will see more about there 26MW offshore project elsewhere, which is going forward. These will be located off the French coast, in a society loaded with bureaucracy, so it is not surprising they are running a little late.

        If you want to “read the tea leaves” a little more closely, you would recognize that Technip was in charge of Statoil’s offshore floating wind turbine in Norway, the very first offshore wind turbine, which was an HAWT (I think a Siemens). Do you think it odd that they are backing an offshore VAWT now, after their experience with Statoil’s project?

        HAWTs have experienced a long innovation cycle with hundreds of millions invested in development, which VAWTs have not. That is changing, however.

        I found your article started off well, and was informative, but I can see that you just have an ax to grind, or can not face being wrong if you are.

        Why don’t you lighten up, and “…consider the impression you are making”, because it is no longer reasonable.

      2. My apologies but VAWTS have been around for a very long time and a lot of money was invested in them. Very smart people tried to make them work and failed. There have been several VAWT wind farms, none of which are producing power today because they proved themselves to be inferior. The Vertiwind has one third of their prototype erected, not the entire thing.

        Your lack of knowledge and understanding of the physics of this space should make you stop and think.

        Here are a couple of additional articles for you to read on VAWTs.



        And with all due respect, the defensiveness is on your side. I’m just pointing out what is obvious based on history, provable performance and theory. If you repeat the extraordinary claims of a third party about their device, expect to be challenged.

      3. Kevin Kirchman · ·

        Be nice, be respectful, be thoughtful.

      4. Having reread my comment to be sure I stand by both the content and the tone. I assume you are trying to state that I am not meeting my own standards. That is indicative of your subjective reaction to being told you were incorrect, not to my framing of the statements or support of them.

        Being nice and respectful from my perspective does not include allowing inaccurate statements regarding wind energy to go unchallenged out of sensitivity for a persons ego and how they might feel about being told they are wrong.

  24. Kevin Kirchman · · Reply

    You say “…VAWTS have been around for a very long time and a lot of money was invested in them. Very smart people tried to make them work and failed.”

    A lot of people who were very smart tried to invent flying machines, and failed. That’s not an argument against a technology, but a good argument about the value code you personally use to decide who is smart. You don’t know what your talking about.

    Case in point, one of your propaganda web sites presents your views on what makes a good business (what are your entrepreneurial qualifications? zero). You point out that sites that attack their competition should be considered disreputable. You say if a company doesn’t have a site splurging to the world what they are doing before they have done it, that they are shady. Then you slander above those who tell the world something without 3rd party verification. Make up your mind–which is it?

    Your whole diatribe here is devoted to attacking a technology that is now _your_ competition. Every success in improving VAWT technology is _your_ enemy, which you will attack with bias, to defend your irrational position.

    You still won’t acknowledge your statement “VAWT blades are rarely… in clean air” is a total misrepresentation. Try admitting that if you have any character or capacity for self-evaluation.

    You won’t acknowledge that you slandered me with a straw-man argument, claiming that I made claims about my business, when I made none whatsoever.

    Then your puffery statement “Your lack of knowledge and understanding of the physics of this space should make you stop and think.”

    How would you know what the state of my physics knowledge is? I’m an Ivy League engineering graduate. The history of science is littered with academic dopes such as yourself who have spent their lives trying to prove things can not be done.

    Mike, sorry, but it is you that is the fraud here. My guess is that you can see the opportunity of better wind technology, and you hate and envy those who are out there doing something to advance it, because they will claim the benefits of those discoveries.

    You want to slander others, from your lofty position of unquestionable omniscience, to make sure advance and free inquiry in the field is stopped. In my honest opinion, you are a true enemy of renewable energy, not a great advocate as you want us to believe.

    1. Here are a couple of points:

      1. To your point about rarely flying in clean air, that’s shown by the vortex diagrams presented in one of the latest links I provided to you. HAWTs do not disrupt the air flow for their own blades. VAWTs do. This isn’t even beginning to be disputable unless you scale VAWTs to hundreds of meters in diameter, which is a nonsensical extreme (not that it doesn’t keep being suggested as a concept).

      2. To the point about best angle to the wind, HAWTs face into the wind which is dominantly parallel to the ground and the blades at 90 degrees to the ground are being hit virtually all of the time by wind which is aligned perfectly to power them. VAWT blades must be seriously sub-optimized as they must provide a useful power stroke in clean air on the upwind side of the device, and a much less productive power stroke on the downwind side in air made turbulent by the device itself. The downwind stroke is not a power stroke. The upwind stroke is just drag with no power provision. Only in the upwind 15 degrees or so is the blade at all in optimal conditions. Once again, this is not disputable, but just basic physics. It’s unclear why you would consider this to be a controversial statement.

      3. The flying machine analogy is amusing, but inaccurate. Some of the material I provided showed clearly that VAWTs were the first turbines built and that they were supplanted by more efficient devices rapidly. I at no point said that VAWTs wouldn’t work, I just said that VAWTs aren’t as efficient. That’s like saying that a jet aircraft is faster than a propellor driven plane, not like saying that propellor driven planes won’t fly.

      4. I looked up everything I could find on you and Sequestra (not much). I pointed out that it aligned well with some red flags I maintain to help people not invest in useless tech in the wind space. I suggested you should consider how you are representing yourself. Hardly slander. My apologies if your statements led me to believe you were directly claiming that your company was building a VAWT and that your claims were for your own device.

      5. Your claim of authority through your Ivy League degree in engineering is interesting, but immaterial, as is your attack on my qualifications. Please understand that I consider your bluster amusing.

      There is no potential for VAWTs to be better than HAWTs. The past 40 years are littered with the rusting carcasses of VAWTs while there are about 300,000 utility-scale HAWTs with a generation capacity of about 320 GW working today in about 100 counties worldwide. They were tested by major labs, NASA and Sandia both tried to make them work and they were installed in farms that failed to produce economical amounts of energy compared to HAWT farms of the same generation. That’s called empirical reality, and unless you think that thousands of engineering professionals, policy makers and purchasing agents are equally deluded, it says that VAWTs aren’t effective and HAWTs are.

      You are rapidly degenerating into ad hominems and accusations of fraud and slander. You are making wild claims without references. Please understand that you must adhere to the moderation policy, and that unless you improve your next comments substantially, they will not be published.

  25. Kevin Kirchman · · Reply

    [Comment did not pass moderation despite warning. Author of comment has been moved to permanent status of requiring approval before comments are published.

  26. Kevin Kirchman · · Reply

    VAWTs do not disrupt the flow of wind to their blades as they make the front pass, which gives them the same area of clear air as an HAWT. And your “hundreds of meters in diameter” comment is the same–it does not accurately quantify the axial flow in a VAWT.

    1. Kevin, as the laminar flow visualizations provided were unclear to you, I developed this simple pair of graphics to assist you in understanding the physics of vertical versus horizontal axis wind turbines. They are now both in point 2 of the post you are commenting on, but for your convenience, here they are.

      This diagram shows the disk of a horizontal axis wind with clean air, turbulent air and the angle of wind to the blades.

      This diagram shows the disk of rotation of a vertical axis wind turbine with clean air, turbulent air and the optimal, sub-optimal and actually negative areas of the rotation of the blades through the air.

      Thank you for making it clear that further explanation was required for some people. The diagrams are useful and I’m sure I’ll find them of value in the future.

      Regarding the “hundreds of meters” comment, the only way in which the blades are not passing through turbulent air downwind which is created by the turbine itself is if the diameter of the VAWT is hundreds of meters. My apologies if this wasn’t simply enough stated for you to understand. I’ll try to not assume anything of your understanding of physics and downwind turbulence based on your Ivy League engineering degree in future.

      1. Kevin Kirchman · ·

        Your simplistic diagrams make it explicit, and acknowledge what I have said, which is that for the whole frontal area, the VAWT blades are in clear air. True, for only one of their two passes (an HAWT only has one per rotation). But the VAWT blades pass in the same amount of clear air as the HAWTs, assuming they both have the same area, which is only fair. You must clearly acknowledge that your statement “VAWT blades are rarely… in clean air” is false, as I pointed out above.

        Explaining further, since HAWTs only make one pass, each VAWT blade provides _additional energy_ from axial flow and from generating lift in turbulent air. Again, that is energy additional to the first pass. That you have not discussed with any technical precision in your criticism of VAWTs. How much can be drawn from this turbulent pass? Well, we could approximate that with a second application of the Betz constant, less energy take from the first pass, plus axial flow. This difference, in fact, alters the Betz constant, as _the fundamental physics of the two turbine types differ_ because of the axial flow. Dabiri has acknowledged this axial flow contributes energy to a turbine, which he calls “vertical flux”.

        I take further issue with your VAWT diagram, which shows regions “Blades creating drag” and “Blades not creating drag”.
        As every trained aerospace engineer knows, including myself, the blades always create drag when going through the air, whether on a VAWT or an HAWT. If you were technically competent, I don’t think you would have made such false assertions. You could say that downwind the drag forces are lower as the relative velocity of the wind is less, but so too is the lift, and contrarily, the drag is greater on the upwind travel of a VAWT blade, but so too can be the lift forces.
        You also fail to make explicit in your drawing that a VAWT with variable pitch blades can be in an “optimal angle in clean air”, depending on the control paradigm. High performance HAWTs have variable pitch blades, so too can VAWTs, and this should be the assumption if a comparison is fair.
        You also say “the only way in which the blades are not passing through turbulent air downwind which is created by the turbine itself is if the diameter of the VAWT is hundreds of meters”. That has no relevance, as even if the downwind blades encounter some turbulence, as every blade of either type does in nearly all cases, that does not eliminate lift production, only altering it.
        Your web site is in general a criticism of VAWTs and those companies who make them. You are willing to dish criticism out, but can’t take it.

        You cannot know, with any certainty, whether some innovative person can develop a better form of VAWT built upon valid physical principles. Because the two turbines are fundamentally different, there are possible advancing opportunities that remain.
        Finally, you say your site “My technology background in computer systems has helped give me sufficient technical depth and breadth to understand wind technologies”, but you are not an aerospace engineer, which is quite a bit different. I know—I have degrees in both computer science and aerospace engineering. I study wind turbine papers regularly. Thus your presumption of superior technical understanding is ungrounded.

        You may understand the latest candle technology, but with that you will not be able to prove a light bulb cannot be invented.

      2. Wow. You refuse to accept empirical proof of poor performance from VAWTs and you refuse to accept the explanation for why VAWTS are so inefficient compared to HAWTS.

        My apologies, but you are so virulently opposed to reality that it’s not worth speaking to you further. You have proven yourself to be a timesuck, not a useful person to speak to.

        I’ll leave you with the edited conversation I had with the CEO of the only certified VAWT in the world. Maybe it will get through to you, although I doubt it.

        Digging Deeper Into The UGE


        Please understand when I don’t bother to reply to you in future. It’s your unwillingness to accept both empirical reality and the theoretical underpinnings of it, not me.

  27. Kevin Kirchman · · Reply

    Again, I never said that VAWTs were not, in their present state of development, of lower efficiency that HAWTs. But that is not “poor performance”, as people producing them generally know what to expect before they produce them.

    The currently state-of-the-art, slightly lower efficiency of VAWTs ultimately will make no difference, as their manufacturing costs will prove to be considerably lower. Wind fuel is free, and that is why efficiency is not the primary issue.

    1. Half the performance and twice the materials used for the same swept area.

      That’s not slightly lower efficiency. Maybe you need Paul Gipe’s perspective on this? He’s only been directly engaged in small wind generation since the early 1980’s, testing all forms of wind generation and driving wind generation world wide. Maybe you’ll actually believe him.


  28. Kevin Kirchman · · Reply

    “Half the performance and twice the materials used for the same swept area”–looking at your reference, which states “The more the relative mass of a turbine, the more its likely cost”.

    Wow, you call that a study? They look at a small, household turbine.

    You keep saying you are discussing utility-scale turbines, but you would be absolutely silly to extrapolate from that one person’s off-hand comment. And Paul Gipe’s comments are only in regard to some particular manufacturer’s turbine, and cannot be reasonably applied even to all small turbines, no matter what design, which is what you are suggesting.

    1. Let’s be clear. This is the only certified VAWT in the world. It’s the only VAWT on the list of best selling small wind turbines among four HAWTs. The results are pretty much the only credible and independently assessed results of any VAWT in existence today. The results are from a device which has existed for years under significant refinement.

      As far as I can tell, the helical Darrieus VAWT is the most effective VAWT design in existence. The Vertiwind which you like so much is a helical Darrieus. The UGE is the most refined version of this design in production today.

      You are resorting to absurd lengths to attempt to hold onto your baseless opinion. And you are doing so without providing any referenced arguments, simply disagreeing with me. Further comments which are not referenced and based in evidence will not be published.

      1. Kevin Kirchman · ·

        [This comment did not meet moderation standards. This is strike two for this commenter. If he is unable to adhere to the moderation policy, he will be one of a tiny number of individuals permanently banned.]

  29. Rich Radley · · Reply

    Very interesting research.
    All VAWT’s are single bearing design.
    If I were to want to purchase a windmill I would choose the HAWT. But I want to do some experiments with VAWT’s design on a small scale. I saw one stuck under someone’s deck, it was used to charge a 12 volt battery overnight.
    Where I live Oil heat, or just about any purchased heat, costs on the average of about $4000 per year for the average home.
    I’m thinking that using Wind as supplemental power source to generate heat (hot water radiant system) might reduce my heating oil bill. I could add an inline water tank that would be only for the basement heat. So this could be a wind mill that needs only operate in the winter and should be out-of-sight.
    One of your major objections to he VAWT is lateral bearing wear. I can see this in all the examples you show except ref (11) Are most all VAWT’s a single bearing design? (no bearing at the top of the blade)
    Your research does show possibilities for VAWT’s as small supplemental power generators that can be used where efficiency is less important and size and quiet are very important. Note winter, noise is of less concern.
    As a further note; we have a wind farm not 5 miles from here with 21 turbines. If I go out onto the deck or open a window I can hear them. Its not too bad and they do shut them down when the noise level gets too high. Pity the people who live a mile or closer. The noise level is very high. You don’t want to live near these monsters. People are selling or abandoning their homes in these areas. I have read the complaints in the news. Its a sore spot for the HAWT’s But the records rarely count those who abandon their homes. Sometimes I think that a lot of small turbines would be better than 21 large ones.

    1. First things first. In general, everybody is better off maximizing efficiency through insulation, etc before adding generation to their homes. And, solar is almost always a better choice for home generation as the next choice. Wind generation at tiny scales is rarely effective by comparison. Where it is effective, it’s on a mast 30 meters high in a clear area where the wind is good. Anything less, it’s hard to justify the expense for generating electricity.

      Regarding noise and home abandonment, you really have to check your sources on that factoid. Have a look at this Australian study before you think that lots of people are leaving their homes.


      1. Rich Radley · ·

        I’m insulated to the max and I can’t seem to get Solar to work at night. So its wind. A High mast not a good choice for home use. what can I do next?

      2. Get cheap electricity from the grid. It’s cheaper than tiny wind.

        If you’ve got an ideological reason for grid independence, feel free to add micro wind generation, but it won’t be justifiable based on anything else.

  30. […] Why aren’t vertical-axis wind turbines more popular … – Simple drag vertical-axis wind turbines have a long history, and a version was used as the first electrical generating wind turbine ever, built by Professor James …… […]

  31. Robert Corman · · Reply


    You are doing a great disservice to the industry as your opinions on vertical turbines are for the most part simply wrong.

    1. You note that utility turbines are placed only in constant wind sites; this is actually part of the problem. In fact if you look at the levelled cost of production background work from the US Nat. Energy Lab you will discover horizontal turbines are getting larger because they can’t achieve efficiency at small sizes and in uneven wind conditions, while verticals can.

    2. In Europe, and soon in the US and Japan, horizontals are going offshore because they are so noisy a NIMBY problem has emerged – coupled with poor performance in most conditions – and they are FORCED offshore (you really should learn something about how this impacts capital costs when you try to build in 300 feet of water). Verticals are quiet, and

    3. they do not guillotine birds and bats (they only have a 30 degree range of vision so they can’t look up or accommodate a H much higher blade speed).

    4. The turbulence model you have for a vertical is fiction, you can muster twice the density of verticals on a given site as you can horizontals because they make comparatively almost no turbulence, this not only allows you to half farm cabling costs, but get the true value out of a great site. In contrast, most H farms have to position most of their towers at less than optimum locations to accommodate their own turbulence.

    5. The latest generation of V turbines incorporate helicopter rotor logarithms for blade pitch control and are consequently about 35% more efficient than H turbines. This is unbeatable because H turbines are forced to extract energy from a plane of wind, while a V turbine can harvest a volume of wind (can you visualize that???).

    6. I could go on and on about every single point you have raised. Please deepen your knowledge before you try to color opinions with your advice. I suspect your intentions are honourable, but your view creates disservice.



    1. Your points are unreferenced and provably false for the most part. Please read more broadly in my site for information on bird mortality for example. As for your claims that intelligent siting in good wind resources is a problem, it merely shows that you do not understand the physics of wind generation. Please feel free to respond with referenced and coherent arguments; these ones are merely incorrect assertions for the most part.

  32. Sam Palomino · · Reply


    I find your responses complete arrogant unjustified and stupid. You seem to get defensive and try proving your point and stand ground when someone disputes your theories. As Robert Corman and others have rightly stated there are benefits to VAWT than HAWT. You need to cover your basics first and do more research than just arrogantly standing ground, please try to accept some amount of criticism, every one is not always right and cannot be we do make mistakes and accepting them is more honorable.

    1. Thanks for sharing. Have anything relevant, factual and referenced to say?

  33. Thanks for the article Mike. One of the first comments you made to an inquiry was that “small wind generation is almost never going to be cheaper than just getting electricity from the grid. Small wind generation isn’t particularly economic unless you are off the grid and willing to live with significant compromises” I suggest that the word “small” should have been replaced with “ALL”

    1. Given that wind power long term purchase power agreements signed for an average of 2.5 cents USD in the United States in 2013, that Brazil had to create separate energy auctions that excluded wind power bids so something else could win because wind is so cheap and given that there are about 340 GW of utility-scale wind generation out there right now, I’d say that your opinion is not backed up by facts.

  34. Bob Smyth · · Reply

    This is not a comment Mike, but a query. There seems to have been some investigation of synchronised power distribution. Has there been any holistic investigation of urban micro generation , including mass production, roll in roll out maintenance, redundancy, storage (including opportunities for micro hydro from irrigation needs for Public Gardens and Forests, transmission (underground), distribution (including local forward distribution of energy generated by electric powered transport) etc., I realise what I am talking about with human produced wind (such as that from traffic, air conditioners etc., ) is in effect re-capturing losses from the friction effect of usage which could be captured in other ways, such as more public transport usage rather than single person cars, more efficient cars etc., but then are there any side benefits perhaps, for example are there any benefits such having a more turbulent, rather than a non turbulent wind behind a turbine ? Again, I am seeking information from someone who obviously knows his field of expertise. I have searched but not found what I wanted yet and have limited time. Your assistance in pointing me in the right direction would be appreciated.

    1. Pretty much all experiments with capturing secondary wind energy from outflows rapidly runs into two problems.

      The first is that wind generators block outflows reducing the effectiveness of the primary usage. The second is that Betz Limit plus other inefficiencies mean that you get a lot less energy out of the system than you put into it. As one example, I calculated that a 75 W ceiling fan powering a wind generator just below the ceiling fan would likely be able to power a maximum 6 W LED and would prevent cooling of the room. It’s much more effective to put an efficient ceiling fan and an LED light both powered by the grid.

      The next problem is dispersed complexity. The smaller the generator and the more widely distributed, the more labour is required to deploy and maintain it. This is completely fine at the level of rooftop solar and utility scale wind, but breaks down when you start putting small things with moving parts — wind generators — in a widely distributed model. The economics curve doesn’t line up.

      Similarly, capturing energy from water flows in cities is equally problematic as the big problem with moving water around cities is ensuring it flows as efficiently as possible. Putting a generator into the mix means putting more energy in to keep the water flowing in the first place and like wind generator from outflows, you lose more than you get.

  35. John(JP) Funk, BSME · · Reply

    As a Mechanical Engineer, and chronic tinkerer/inventor I have toyed with the idea of ultra-small scale VAWT turbines as a way to ultimately reduce the initial cost of turbines(using automotive alternators as generator), but after doing some basic research there became two glaring problems with VAWT’s that simply could not be overcome inexpensively. The first was the resistance caused by the trailing blade in the “dirty” air(my design used a collapsible “sock” to minimize wind resistance until the vane came back into “clean” air, and the second was getting the turbine into “clean” air in the first place.
    The primary factor that makes an HAWT more efficient than a VAWT is the “Swept Area”, which in an HAWT is pi times the square of the radius. In a VAWT the swept area is twice the radius times the height. It doesn’t take a very smart calculator to see which “Swept Area” grows faster in scale.
    Those who would attack Mr. Barnard without evidence should look at the empirical evidence that surrounds us in the “real world”. How many VAWT wind farms have you seen in the past year? The market drives innovation, and if VAWT’s had any real potential they would be moving to the fore, and not living on in the idealistic dreams of overly “passionate” proponents. I can’t help but come to the realization that in order to generate equivalent power at low heights, you must necessarily have high density VAWT turbine siting, which in turn makes all of the air “dirty” behind the first row of turbines. It’s a nonsensical argument, no matter how “passionately” you feel.

    1. Mike, my point was that wind costs more to produce on any scale as opposed to coal fired and nuclear plants. The US Department of Energy and Wikipedia disagree with your notion of “cheap” wind power.

      1. You continue to make false assertions without references.

        First off, wind scales better than nuclear. This is empirically proven by the example of China which has been on a massive build out of both for the past decade and yet has barely turned on any nuclear compared to the wind generation that they put in annually.


        Regarding price, you continue to be wrong. First, you have to start with apples-to-apples comparisons of new generation to new generation and second use full lifecycle costs of electricity. Looking at existing coal or nuclear plants which are fully amortized, or in the case of nuclear where the debt has been shifted to a third party and is not included in the price of electricity, is not the appropriate comparison.

        Looking at one credible — and referenced source – the US Energy Information Administration, we can see the following:

        Coal – $95.6 per MWH
        Nuclear – $96.1 per MWH
        Wind – $80.3 per MWH


        Not that new wind generation is much cheaper than the nuclear and coal generation you prefer.

        Of course, that’s one perspective. The reality is playing out differently. The International Energy Association pegs new nuclear at $110-$130 per MWH. The Hinckley nuclear example from the UK is at $150 per MWH. The Vogtle nuclear example in the USA is at $110 per MWH. These are all much higher than wind generation.

        As pointed out in my earlier comment, wind energy in the USA averaged $25 per MWH on long term PPAs signed in the USA, which is an apples-to-apples comparison. If you add in the PTC and transmission costs, it’s still less than $50 per MWH. This is very close to worldwide numbers as well, with Brazil averaging a hair over $50 per MWH for the past couple of years of signed PPAs.

        So once again, your numbers are incorrect and wind generation scales just fine.

  36. Val Martin · · Reply

    For novelty applications vertical and horizontal small wind turbines are fun and educational. For mains electricity supply industrial wind turbines do not provide any net electrical power over one year. They do make money from huge subsidies. See my vireos valmartinireland you tube.

    1. Wind turbines produce vastly more energy than they consume. De-icing is just starting to penetrate the market, air-conditioning doesn’t exist and published and reviewed lifecycle cost analyses (LCA) following ISO methodologies suggest that electrical consumption by wind towers is insignificant, so the ratio is extremely high. The Hepburn wind farm in Australia produces 302 times the energy annually that it consumes. http://barnardonwind.com/2013/03/02/parasitic-power-and-wind-turbines-sounds-scary-but-whats-the-real-story/

      1. Mike, did you even view one of Val’s video’s? The evidence he produces is very compelling, especially in video # 2

      2. No. I didn’t bother to go to a random wind crank’s video of made up nonsense. I’ve read grid management studies, peer-reviewed material and studies on the economics and payback of wind farms. Refuting something as completely ludicrously false as Val’s statement on a point by point basis or even wasting time looking at it is unnecessary. It didn’t follow moderation policy — off-topic, not referencing primary sources — and I only bothered to allow it to be posted so that I could provide the quick refutation material.

        As the moderation policy says, if you have an argument, make it and provide primary sources directly, just as I do.

  37. David · · Reply


    I have found your article and following discussion to be very interesting.

    Do you think that there will ever be an efficient solar panel equilient of wind power where home owners can generate power using a cost effective modular system.

    If the answer is no and the Hepburn wind farm a model to follow where many indivifduals come together to achive a collective gain, how would city people go about achiving a simialr outcome

    Keep up the good work


    1. Hi David . . .

      Thanks for popping by. Right now rooftop solar is cost-effective for homeowners in a lot of places, but especially places with time-of-use billing. Electricity rates are increasing everywhere in any event, but time-of-use billing starts to push things like 45 cents USD per KWH peak price in California, and that price lines up very well with solar generation timing during the day. That’s why companies like Solar City and Sun City in the USA are able to offer zero-down leasing on solar systems while also reducing their customer’s total monthly expenditure on electricity including the price of the lease. We’re already there for cost-effective home solar.

      As for great initiatives like Hepburn, I’d point you to two things:
      1. Windshare.ca – It’s a coop set up with mostly Torontonians who got together and built a 750 KW wind turbine at Exhibition Place on the waterfront of Toronto.
      2. Germany, where coop ownership of wind farms is much more common than it is in North America.

      Closer to home, Simon Holmes a Court, who was heavily involved in Hepburn, is actively working to make community renewable power generation projects more viable through one of his companies.

      Lot’s of good stuff going on here, but part of the challenge is that there are good business models for corporations who don’t have the overhead of coops in terms of governance, so they have tended to scoop the good wind sites and build the wind farms in many parts of the world. That’s the problem with wind farms being a good business model; competition is stiff.

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