Wind Power: Are Vertical Axis Wind Turbines Better?

Wind expert Mick Sagrillo discusses vertical axis wind turbines, a recent innovation in wind power.
By Alison Rogers
February/March 2008

Vertical axis wind turbines aren’t quite ready for the masses.
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Worldwide interest in renewable energy options has given rise to a rash of new wind turbine designs. Some of the most recent models on the market are vertical axis wind turbines (VAWTs), which manufacturers claim are quiet, efficient, economical and perfect for residential energy production, especially in urban environments.

We asked Mick Sagrillo, veteran residential wind power authority, to answer our questions about this technology and its future in the realm of alternative energy.

First of all, how does a vertical axis wind turbine work?  

There are actually two different designs out there. One’s called a Savonius rotor, which essentially, if you take a 55-gallon drum and cut it in half, then offset the two halves and put them on a shaft that rotates, you’ve built a Savonius rotor. It’s similar to an anemometer. A lot of what we see today are Savonius rotors. They’re very crude, very low-tech, very inefficient. We’re talking about something that operates in the, say, 5 to 10 percent efficiency range. People have been able to tweak the efficiency rate — ideally, they might be as high as 15 percent.

Then there’s the Darrieus model — the type that resembles an egg beater. Essentially, you have two vertically oriented blades revolving around a vertical shaft. But the Darrieus models use an airfoil design. A wind turbine airfoil works in the same way as an airplane wing. An airfoil has a flat side and a curved side. The result of air passing over the two sides is a force known as “lift.” When an airplane speeds down a runway, air passing on both sides of the airfoil wings, the lift force literally lifts the airplane into the air. This will continue as long as there is forward motion over the airfoil to generate the required lift.

A wind turbine uses this same principle, but instead of flying up and away, the airfoils are secured to a hub, which in turn is attached to a generator shaft. The air passing over the airfoils (wind turbine blades) are converted into rotational momentum which spins the generator.

On the Darrieus rotor, since the airfoils are the same as horizontal axis wind turbines, they will operate at the same efficiency. However, the difference occurs because a horizontal axis turbine's swept area always faces the wind. But with a vertical axis wind turbine, the swept area is a cylinder perpendicular to air flow. As such, part of the “swept area” is working, while part is simply being blown around, not at an optimal angle to generate lift. This results in a vertical axis wind turbine rotor that is less efficient than a horizontal axis rotor.

Anything with an airfoil, ideally, can be 59.3 percent efficient. In reality, a horizontal axis turbine operates somewhere around 35 percent. A vertical axis turbine is lower, maybe attaining 30 percent, which doesn’t sound like much, but other factors such as increased maintenance and lower energy production add to the difference.

The vertical axis wind turbine manufacturers claim there’s less wear involved because they don’t have to actively orient themselves to the direction of the wind. That’s actually untrue; it’s just the opposite. There are lots of claims relative to the fact that a vertical axis turbine can take winds from any direction, well, so can horizontal turbines. There’s actually more wear involved with the VAWT. I have a rubber ball on the end of rubber band. When I spin it around slowly, it makes a circle, and if I spin it fast, the rubber band stretches and it makes a bigger circle. That’s centrifugal force. So anything that spins and has mass has centrifugal forces working on it.

The interesting thing about horizontal axis turbines — and this is just a fluke of physics — has to do with the way the airfoil is designed for horizontals. The greatest stress on it is at the root of the blade near the hub, which happens to be the strongest part of the blade. On a vertical, if it’s the egg beater shape (sort of an oval), the greatest forces are at the center, not at the ends where it’s attached. If you make the blade straight it distributes the force more equally, which is where designs have gone recently, but there are some intrinsic problems with vertical axis design and centrifugal forces that really can’t be overcome. It’s just the nature of the design.

So there’s actually more wear and tear on a VAWT. The way they overcome that is by beefing up the design. This is why you don’t see vertical axis turbines commercially viable in the United States today. The manufacturers must use more materials, which means more labor. This also means that vertical technology weighs more. You have a bearing on each end that has to be supported, and it’s easy to do that at the bottom end but hard to do on the top. If you end up putting it on a tower, you need guyed cables that extend for long distances in order to clear the rotor.

Some inventors say that you can put it on a building or on the ground, which eliminates the guyed cable problem. Well, you can, but they need to go back and learn something about fluid dynamics. The reason turbines are on towers is because that’s where the wind resource is. Fuel increases as we increase our distance above the earth. Along the ground we have this zone of friction, and as you get away from the friction, you get faster moving air.

Enter buildings. Why not a building? Think about a flag pole in the city, and the flag is bobbing around and changing directions. If you go out to a school in the country, with wide open spaces, that flag is just straight out. You’re looking at the effect of ground clutter. Trees, buildings — all of that stuff creates turbulence. There are two problems with turbulence. Number one, wind that changes direction and speeds that go up and down translates into a lot of wear and tear on the turbine, which translates into a shorter life. The other thing is, there’s no power in ground-level wind. It’s just chaotic motion. There’s no real energy.

So the pitch and the rise of a roof wouldn’t accelerate or concentrate the wind’s energy? That’s bogus. That concept works and is actually true when you’re dealing with landforms. When dealing with terrain and topography, you’ve got a very wide, open area, miles around, and you’ve got a ridge that’s perpendicular to the wind. What happens is, when the wind approaches that ridge, it is compressed and the flow actually increases. When you deal with a building, wind goes around and just tumbles over it. They’ve downscaled the idea of topographic fluid dynamics and applied it to buildings. It’s not accurate, which has been very well documented with flow studies. The wind trips over obstacles, and when it trips, the wind can’t do the work it could have done without the obstacle. You’re creating turbulence and diminishing the quality of the wind resource. With wind, we’re dealing with quantity, yes, but we’re also dealing with quality. You want a nice fluid flow, not turbulence.

They seem to be gaining some popularity among consumers. Do they cost less? You know, it doesn’t matter. It’s not about initial cost. It’s about energy production over the 20- to 30-year-life of the turbine. Vertical technology is less efficient — the return on investment in terms of cost per kilowatt hour isn’t as good.

The whole thing is not about spinning. You can buy a pinwheel that spins. It’s really about generating electricity, and doing so reliably over many years. The vertical axis technology has just not been able to survive in the market.

There’s appeal for them in the marketplace because there’s something so visually appealing about a vertical axis turbine. There are actually studies in Europe showing that people are mesmerized by windmills. It’s called the frequency effect. It’s akin to sitting on a shore and watching waves come in, or a campfire, or wind on prairie grasses. The studies show that people are more fascinated by vertical axis turbines than horizontal, for one reason because you don’t see them as frequently, for another reason because verticals don’t have this tail moving around, which can be distracting, depending on how the wind is moving it around. People are fascinated by the technology because it’s very soothing. There are a number of inventers that take advantage of that.

Are better models on the way? It depends. Unfortunately, too many of these things have been created by self-styled inventers, people that have no engineering background, no physics background, no math background. They just sort of make something up. I know someone that came to me and said “Mick, I want to make a savonius rotor. I know that it’s not cost-effective. But if a person could make it inexpensive enough, and yet reliable so it lasts for decades like the horizontals do, would you support it?”

And the answer is absolutely yes. I don’t care if it’s vertical or horizontal. It’s all about what survives, what works, what generates electricity over the decades. It’s about fantasy as opposed to reality. It’s about things that really work as opposed to things we pretend to work, or want to work. So he had an engineering background, but didn’t know much about wind. And the interesting thing about this is, number one, the design has evolved from an inefficient Savonius rotor to a Darreius, and two, he’s been working on this thing for a couple of years with a real engineering firm that has been doing testing for wind for decades. He’s going about this the proper way, instead of tweaking it and making outlandish claims. He has attracted the attention of NREL, who are just a skeptical as I am about vertical technology. They’re going to take one of these turbines to test it. And I’m actually excited about this because he started out with a dream, educated himself, hired the right people. Because his idea was to make something that’s reliable and  inexpensive enough to make up for the efficiency factor, and I think the guy may have something. I honestly think that in a year or two, we may see a commercial product that actually works and works for 20 years or so like it should.

So we’ll finally see some performance numbers? That’s my whole thing: None of them do. It’s like here’s this new technology and we want you to buy this. We want you to fund this. I say, “OK, send me the production numbers because it’s not about vertical, it’s about reliability, cost per kwh and how many kilowatt hours the turbine is going to generate in a month or a year.” But they can’t send you that. Because they haven’t tested it, or they’ve tested it and the results aren’t good, or they don’t know how to test it, and so on. It’s ridiculous. If you go to companies that have a good reputation in the small wind market, they’ve got that performance or production info. They may offer a power curve — so what? A power curve is like a horsepower curve for your vehicle, it has no bearing on reality at all. What you need to know is how many mpg are you getting? You’re selling this thing for $20,000 or $30,000 dollars and you can’t afford to put $500 dollars worth of equipment on it to monitor its output? That’s somewhat amazing to me.

Are they less noisy? No. I’ve heard very quiet machines and I’ve heard very noisy machines, in both horizontal and vertical axis technology.

Are there any situations in which a vertical model would be a better choice than a horizontal?  Not today. Simply because there’s nothing reliable, there’s nothing cost-effective, there are no performance results, there’s no reality. That could change.

The bottom line is, vertical axis wind turbines are less efficient, and it takes more materials and labor to make the things. It’s pure economics. Things make it in the marketplace because number one, they work, and two, they’re cost effective. If you have a technology that’s more cost effective and more reliable, than the competing technology, the competition is going to fall out of the marketplace. And that’s exactly what’s happened, commercially speaking. We did see, in the early 1980s, a commercial wind turbine, developed by DOE and Alcoa, used in a wind farm out in Altamont Pass. They kept them going for a long time until investor money ran out they couldn’t keep up with the maintenance, let alone get it to output enough energy. So they have all disappeared. There’s a lot of conspiracy-theory allegations out there. “It a suppressed design, etc.” No, these have been around for 80 years and it’s just a shake-out in the marketplace.


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Post a comment below.

 

sTuttle
8/12/2013 11:38:17 PM

I have never seen an apples to apples study of both the VAWTs and HAWTs with the same footprint in same wind conditions.  I intend to do just that, and will report what I find.  Half of the wind exposure is of not motive power with a VAWT and that must be addressed.  Also, the misconseption is that the VAWT blade is like that of the typical Air Foil.  It clearly isn't and furthermore, has not been designed to take advantage of external and internal air flow on the half that is exposed to power extraction.  So I have a lot to do.  I'll keep you informed.


Daedryn Leviathos-Young
2/1/2013 1:37:01 AM
what about the bats?

Ananda Wijesinghe
7/28/2012 12:07:30 AM
As an engineer who has built and tested several VAWTs (and HAWTs), I concur with most of the author's statements: VAWTs are indeed less efficient because all of the blades are not optimally oriented to the apparent wind during rotation, they are heavier and use more materials, the wind resource is generally poor in built up areas, and theVAWT rotor is subject to greater pulsating stresses. Having said that, if one is constrained to use a built up urban location with gusty turbulent wind, the inherent independence of VAWT designs of the wind direction is a distinct advantage. In such locations, small HAWTs fail to rapidly re-orient themselves to the fluctuating direction of the wind and accelerate long enough to produce sufficient power and capture the wind energy. Thiscontinual hunting for the wind is a distinct drawback of HAWTs in such locations. Therefore, it makes sense to build VAWTs ... specially designed to exploit both low and high speed albeit gusty winds .... in urban built up settings, even at the higher cost of energy required to assure increased efficiency and reliability. For many people, such a VAWT can often be justified on a cost-benefit basis, given that they have to use the site they have access to setup the turbine.; This is the goal of most people working on small VAWTs today.

Alpha
7/15/2012 9:43:12 PM
This article reminds be of the 99 scientist out of 100 scientists who said the a wind powered land vehicle could not go faster than the wind speed. They were wrong. Its just his bias to see things in one way. Even if a machine is only 10% efficient, if is works 24 hours a day then you have a viable power source compared to solar or horizontal axis that is not going to be installed in anyone backyard anyway. The loses of centralized power generation are huge. So the horizontal axis generators in Palm Springs are less then 10% effcient by the time the power gets to San Francisco. To read Steve Jobs' biography was enlightening. Nothing that eventually made Apple computer successful was possible according to engineers.

leahcimsor
3/23/2011 6:58:00 PM
I think Mr. Segrillo is qualified to comment as he has. He seems to favor renewable energy. He dosen't seem to be anti any particular technology just taking a fact based stance : http://www.greenenergyohio.org/page.cfm?pageID=198 He has many years of experience with wind and other renewable energy systems for home use. His understanding of the physics seems good, and when he states an opinion he says that's what it is. He lays it on the line what it would take for him to change his mind - test results. I will venture my own opinion now. VAWT look very nice (until they start to come undone). If you look at one in a low wind setting it is hard to imagine what they are subject to in a good wind resource. You can go to NREL and see what happened to the first Mariah Power Windspire that was tested. http://tinyurl.com/4d3oc22 They get sustained 50mph winds there. I have done some product design and a million operations of even a small and lightweight mechanism may have trouble with a million operations. If a VAWT spins at 30RPM that is one million stress cycles every 23 days. 15 million cycles a year and 315 million cycles over a 20 year payback period. Given the forces that are involved and the huge number of repetitions, it makes a lot of sense that VAWT have a harder time with durability than HAWT. And given that handicap in order to too survive they use materials less efficiently, cost more, require greater development time, and more maintenance and repair. Cou

tony deckard
1/28/2011 9:08:55 PM
Seems to me this article is the antithesis of what MEN has always stood for. Whether vertical is feasible or not, the idea that one must have degrees and a proper background to come up with, and implement, good ideas is ignorant. I sincerely hope this author has learned something in the last three years.

Eric B
9/20/2010 10:14:42 AM
Link with 2 brief excerpts: http://www.theoildrum.com/node/6954 12 Small Wind Turbines Tested in the Netherlands The Dutch coastal province of Zeeland (a very windy place) placed twelve of these much hyped machines in a row on an open plain (picture above)…. Two real-world tests performed in the Netherlands and in the UK confirm our earlier analysis that small wind turbines are a fundamentally flawed technology. Their financial payback time is much longer than their life expectancy, and in urban areas, some poorly placed wind turbines will not even deliver as much energy as needed to operate them (let alone energy needed to produce them). Given their long payback period relative to their life expectancy, most small wind turbines are net energy consumers rather than net energy producers. The machines face two fundamental problems: there is not enough wind at low altitudes in a built-up environment, and the energy production of a wind turbine declines more than proportionately to the rotor diameter. Wind power rules, but small wind turbines are a swindle.

Tom_54
9/17/2010 6:46:54 AM
This gentleman is biased. He probably works for a HAWT manufacturer and is using outdated information. Not once does he mention problems associated with the horizontals, such as blade flutter and fatigue, exploding blades due to over spin,(http://www.liveleak.com/view?i=cdd_1203701257) etc. This, in addition to being bird and bat killers makes the HAWT a poor choice no matter where it is installed. There have been, and continue to be many advancements in VAWT's, including verifiable performance testing. Typical performance failures are due to improper siting. When people hear these are good for the urban environment, they think it means VAWT's can be installed anywhere. Since the engineer spews his opinion throughout the article, I'll take my turn. In my opinion, the VAWT is superior to HAWT in that it produces very little vibration, produces usable power in low wind conditions, operates silently and doesn't kill wild life. Oh, yeah, and the blades don't explode!

Tom_54
9/17/2010 6:46:53 AM
This gentleman is biased. He probably works for a HAWT manufacturer and is using outdated information. Not once does he mention problems associated with the horizontals, such as blade flutter and fatigue, exploding blades due to over spin,(http://www.liveleak.com/view?i=cdd_1203701257) etc. This, in addition to being bird and bat killers makes the HAWT a poor choice no matter where it is installed. There have been, and continue to be many advancements in VAWT's, including verifiable performance testing. Typical performance failures are due to improper siting. When people hear these are good for the urban environment, they think it means VAWT's can be installed anywhere. Since the engineer spews his opinion throughout the article, I'll take my turn. In my opinion, the VAWT is superior to HAWT in that it produces very little vibration, produces usable power in low wind conditions, operates silently and doesn't kill wild life. Oh, yeah, and the blades don't explode!

John M Carter
5/11/2010 12:33:35 AM
Savonius rotor, the design being just to barrels cut in half. If the machine is built the way it was originally designed to be Mother Earth New's would think twice about their statement . my late Grand father Galen B. Schubauer was a physicist who worked for the Burrow of standards in Washington D.C. Dr. Schubauer redesigned the old version of the Savonius wind rotor so it would allow the air to flow through easyer with less drag . His redesigned is very simaler to ex. of what Fitz Water Wheel company gave by improving on an old design. To the water driven grain mills . G.B. Sububauer put a copywrite on his redesigned s-rotor , so The Schubauer s-rotor with a long shaft attached to the shaft with a special designed propeller, kept our dock free of Ice! for close to ten seasons . My Grandfathers invention saved close to $1500. per year. If we relied on a traditional eletric Ice eater ,it would have costed us alot more then just minor fixes . Sincerely yours, John M. Carter

Tom Kregel_2
5/7/2010 10:24:32 AM
Isn't it about time for Mother Earth News to compile a spreadsheet of costs and efficiencies for all the brands and models available for residential use? Let the numbers speak for themselves. One column could be Vertical vs. Horizontal. Others are maintenance costs, initial set-up costs, required height, wattage at various wind speeds, noise level... Where can one go for this across-the-board type of data? Even better would b a competition where many different brands and models are set up in the same field and see who makes the most wattage. I am in the market and do not know who to believe.

Jan Steinman
4/30/2010 11:23:35 AM
Hi cites TWO DESIGNS and then writes off ALL vertical-axis machines? I might agree with him that if you limit yourself to Savonius and Darius designs, horizontals are better for most applications. But horizontals (and the author, it seems) are so mainstream. The real creative work is going into verticals. Here's an example (actually, the patent) created by a "guy down the street," "in his garage," that eliminates all of the objections Sagrillo raises: http://www.wipo.int/pctdb/en/wo.jsp?WO=2009018666

Bob Braafhart
10/1/2009 3:26:40 PM
Thank you Mother Earth News for all your great work. I have read this person's comments before and it is clear there is not love lost by him on VAWT. I believe one great thing they have done is to create interest and to sparked to life the inventor in many of us. Even more so it has fanned to flames interest in something that could create energy from an abundant renewable resource. In that arena, I believe they achieve a 90% efficiency rating.

Gene_15
5/7/2009 6:46:37 AM
I am working for a custom sheet metal fabrications shop and I have been talking with engineer who doesn't know wind and an experienced HVAC designer that understands wind (airflow) but doesn't get everything with the Betz' Law, the concepts that I have, etc , etc... and I talk to them but they cock their heads to the side and think I am out of my mind. The author definitely has some bias in his words. I hope to field test this coming winter a variant of the savonius type out on the south shore of Long Island and a few on my roof (after I get a thumbs up from the Town supervisor) Stay Tuned!

jon_23
4/1/2009 1:29:44 PM
why is it that noone ever mentions the wind ship alcion launched over 25 years ago which proved vertical wind technology works it was completely self sufficient once the foreward movement was 2kts it powered all its electronic and drive functions, which it had or should i say has quite a lot. the only problem with it is that the custeau society seems to keep tight wraps on the design.

WINTER Star
3/24/2009 10:00:49 PM
Seems this guy has not seen them all, after all. Waht about that double-helix config. unit in Chicago? They have measured and statted that, and it seems to be doing very well, turbulent winds and all. OR, maybe that one has such cheaply replaced membrane fins, that makes up for being short-lived?

Larry _1
3/24/2009 1:57:08 PM
This article is awful. The writer is full of opinion. Im an engineer too but I don't use it to club young inventors over the head. Millions of guys have passed those tests pal get over it. It's really not true what your mother said about you being the smartest boy in the world. After accusing Vertical Turbine makers of failing to provide statistics the writer fails to provide us with any useful statistics of his own.. terrible engineering article

Pedro_2
2/26/2009 5:37:06 PM
Great article! I had the chance to check out Mariah Power's Windspire since I live near their Reno HQ (http://mariahpower.com). What a great product: made in the US, pretty much silent operation, starts in low wind speeds, 90+% recycled materials (yes, made from YOUR Coke cans). Check em out and support a US company making clean energy products right here in the US!

Pedro_2
2/26/2009 5:35:20 PM
Great article! I had the chance to check out Mariah Power's Windspire since I live near their Reno HQ (http://mariahpower.com). What a great product: made in the US, pretty much silent operation, starts in low wind speeds, 90+% recycled materials (yes, made from YOUR Coke cans). Check em out and support a US company making clean energy products right here in the US!

Testing_1
11/21/2008 12:07:44 AM
testing testing

Testing_1
11/21/2008 12:05:46 AM
testing testing

laurie_2
9/29/2008 12:02:17 PM
One aspect that should be weighed in any design review is the impacts on wildlife and environment. We know that traditional commercial sized turbine designs kill birds and bats. And despite some reports, the numbers can be quite high in some situations. New designs that reduce this environmental cost should be encouraged.

Susumu
1/23/2008 9:16:25 AM
We completed an efficient vertical axis wind turbine after 18 years' development, see our website www.etllc.org.








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