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

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. 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. 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.  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 more material to generate less electricity resulting in an even lower 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]

References:

[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/

42 comments

  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 …

        http://www.gizmag.com/dabiri-fish-school-wind-farms/28355/

        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.

        Cheers,
        Mike

      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,
        Drew

      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

        http://www.smallwindcertification.org/applicant-turbines/

        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.

        http://dabiri.caltech.edu/publications/Da_JRSE11.pdf

        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

        http://dabiri.caltech.edu/publications/FLOWE_APSDFD_Nov2011.pdf

        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

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