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The Scoop on Vertical Axis Wind Turbines

3/16/2009 9:32:00 AM

Tags: wind turbines, Dan Chiras

One type of wind turbine that’s been getting a lot of attention these days is the vertical axis wind turbine. Even famous Hollywood stars like Ed Begley, Jr., are touting their supposed advantages over conventional wind turbines.

In a vertical axis wind turbine (VAWT), the blades are attached to a central vertical shaft. The shaft is attached to an alternator located at the bottom of the shaft, sometimes even at ground level. When the blades rotate, they spin the rotor of the generator, producing electricity.

Vertical axis wind machines have been around for a long time, about 3,000 years. The reason you see so few of them is that they’ve failed miserably.

That hasn’t stopped inventors (who are apparently unaware of their disappointing history) from rolling out new models and singing their praises. One refrain in their song of praise is that VAWTs can capture wind from any direction, which is true of horizontal wind turbines, too. The difference is that VAWTs are always oriented into the wind whereas conventional wind turbines turn into the wind as wind direction changes, thanks to the tail vane. No big deal there.

Proponents also like to claim that VAWTs are immune to turbulence that wrecks havoc with horizontal axis wind turbines (HAWTs). Turbulence is crazy airflow that occurs downwind from buildings and other obstacles on the ground, known as ground clutter. In turbulent areas, winds can flow in a number of different directions. This, in turn, is pretty hard on conventional wind turbines and one reason they are mounted on tall towers. Tall towers place them in the smoother, stronger, more energy-rich higher-level winds.

The VAWT does have a slight advantage in dealing with wind direction shifts, but turbulence also wreaks havoc on their blades, increasing fatigue. Fatigue leads to failure. Blades can crack and break.

Another supposed advantage is that VAWTs can be mounted close to the ground — even on top of buildings — where they capture ground-level winds. This eliminates the need for tall and costly towers and the need to obtain the zoning variances sometimes required to install horizontal axis wind turbines on tall towers.

Although VAWTs can capture ground-level winds, just like any turbine installed on a short tower, ground-level winds are subject to friction. This slows wind down as it sweeps across the land. Both friction drag and turbulence in lower-level winds around buildings and trees decrease the power available to a turbine mounted at ground level — so much so that there is very little extractable energy in them. The lower the wind speed, the less electricity a turbine will produce.

In addition, dead air spaces form behind buildings and other ground clutter. Placing a VAWT in such a location renders it useless. Even though you can mount a VAWT at ground level, there’s not much energy for them. You could mount a solar electric module inside your garage, too, but it’s not going to do much.

Unfortunately, years of experience with VAWTs has been rather discouraging, to say the least. Hundreds of commercial VAWTs were installed in California in the late 1980s and early 1990s. They all failed and were removed from service. These were not experimental units, but production units.

VAWTs are also less efficient than horizontal axis wind machines. For a given swept area, they just don’t extract as much wind energy as a well-designed HAWT. In addition, the blades of VAWTs are prone to fatigue created by centrifugal forces as the blades spin around the central axis. The vertically oriented blades twist and bend as they rotate in the wind. This causes the blades to flex and crack. Over time, this causes the blades to break apart, leading to catastrophic failure.

VAWTs are less reliable and efficient than HAWTs. All in all, they just don’t stack up against horizontal axis wind turbines. Don’t be fooled by the chatter of the ill informed — our friend and ally Ed Begley, Jr., included.

To learn more about VAWTs, check out Wind Power: Are Vertical Axis Turbines Better? You also may want to sign up for some of our courses at The Evergreen Institute or read my newest book, Power from the Wind. This book should be available by mid April in major bookstores and online at The Evergreen Institute and New Society Publishers.


Contributing editor Dan Chiras is a renewable energy and green homes expert who has spent a lifetime learning life’s lessons, which he shares in his popular blog, Dan Chiras on Loving Life. He’s the founder and director of The Evergreen Institute and president of Sustainable Systems Design. Contact him by visiting his website or finding him on .



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Post a comment below.

 

BootDr
11/28/2014 4:40:02 PM
Look at TMA Wind's VAWT at www.tmawind.com

Luann Elizabeth
8/6/2011 2:50:56 PM
What ever happened to the technology that created a beautiful "windmill" that spun silently with virtually no breeze at the 1976 Toward Tomorrow Fair in Amherst MA? I keep trying to find a wind turbine like that one. There were just two blades that twisted a half turn from top to bottom (as I remember it). Or has it gone the way of the electric car? (see DVD: Who Killed the Electric Car?)

wind generator_1
5/30/2010 1:46:35 AM
Wind turbines are used to generate electricity from the kinetic power of the wind. Historical they were more frequently used as a mechanical device to turn machinery. http://www.windturbinestar.com/

Ron Rickert
4/5/2009 9:23:28 PM
Your article is totally favoring the Horizontal axis designs and your opinion does not address the basic need to get small green wind power integrated and funded into small businesses at the grassroot level. Large HAWT's will never gain approvals in urban areas and the Small vertical axis wind turbines up to 10kW remain a great market for the USA and the Caribbean based on utility rates, wind speeds and site conditions. Even thou VAWT's have failed over the years- so have HAWT's, your article should have concentrated on the technology which has greatly improved in terms of chemical / materials engineering -design and CADD engineering which take VAWT's to another level that HAWT's cannot compete. Your article also states false items that you should be retracting and review real companies that are turning heads with their turbine designs like www.tangarie.com. Another major point that should have been raised is that people just want attractive noiseless green power to change the way we produce energy and become less dependent on imported oil. If you feel there are NO valid VAWT companies, why did you not mention them by name? Lastly, why not add a point that not all places are windy and tell people that the higher the wind the quicker the payback or tell them to seek solar and geo-theraml as an altenative. Thank you

Bernard Schaer
3/27/2009 7:50:01 PM
Hi Dan, I enjoyed reading your article on vertical wind turbines. Your articles don't mention, how much of a favor those folks who install a wind turbine or solar panels are really doing their power company under the existing "net-metering" scheme. Please read this article: http://www.thedailycrock.com/?p=607 and let me know what you think. Best, Bernard Schaer

chris_52
3/24/2009 9:52:15 PM
VAWT only have a small portion of the blades able to catch the wind at any given time. The other blades are rotating back to the place to capture more energy. By contrast, HAWT always has all 3 blades positioned to capture the energy throughout the rotation. Given that observation, how are VAWT more efficient in capturin energy as has been stated? Chris

Dave Anderson_3
3/24/2009 5:53:56 PM
You also may note that the helixwind.com output averages are quite negligible if you look closely...and do the math. They use m/s (meters per second) which you need to multiply by 2.2 to convert to mph. In an 11mph (5 m/s) average wind, they represent that their 2.5kw turbine will produce 800kwh in one year. This equates to 67kwh per month from a 2.5kw turbines. 1kw of solar in a sunny place should produce more than that. 67kwh per month equates to a $6.70-13.40 per month ($80-$160 per year) payback, with utility rates of $.10-.20 per kwh. Well, on the bright side, if the helix turbine is priced around a buck a watt, with installation, it might make some financial sense. Actually...hold that thought. At a buck a watt installed ($2500 for a 2.5kw unit, including tower, labor, permits, etc...yeah, I know, I'm dreaming), this would equate to a 15.5 to 31 year payback (@ $.10-.20/kwh in a 11mph average wind zone). I may be wrong, but in reality, I am guessing that the turbine runs at least $15k installed, which could equate to a 94 to 187 year payback time period. Hmmmm. The Feds are offering 30% back on the installed price, so that would make your payback time on the turbine 65 to 131 years, depending on the installed cost variable of course ($15k was used here as an example with utility rates of $.10-.20 per kwh). Anyone know what the price of the helix turbines are? Dave

Dave Anderson_3
3/24/2009 4:39:37 PM
Tom, Although Dan's article is definitely off base with regard to credible research on his part, one thing that you may want to be wary of with helical designs, such as helix, is that it is well known that they need very high winds to reach their "rated" outputs because they simply don't capture much energy, but they look cool...gotta give them that. I've had friends try to obtain the wind speeds at which such designs reach their "rated" outputs and the companies have yet to reply with an answer. You may note on the helixwind.com spec sheets, that the rated output of 2.5kw is nearly the same as their maximum output of 2.81kw. This would lead one to believe that the "rated" output wind speed of the turbine is nearly the same as its survival (or maximum) wind speed. Survival wind speeds are quite high with VAWTs of that nature (60+ mph, which is not posted on helix either...hmmm)). This type of marketing can be far more damaging to this new industry than Dan's article may have attempted to be. When products are sold as turbines and turn out to be little more than wind art, in places other than gale force winds, it is a shame. Dave

Tom_54
3/23/2009 12:52:22 PM
So, Mr. Chiras was a professor??? Certainly couldn't tell by his commentary. For people living in urban environments, the VAWT is the only answer to wind power collection. We do not have the room for guy lines and our city building codes do not allow for very tall towers and our neighbors do not like the noisy blades of the HAWT. Besides, HAWT are ugly as compared to ohhh, let's say the Helix (helixwind.com) Roof mounting is the ideal set up because (typically) it is the highest available spot and, most importantly, winds gain speed and pressure (power) as they are forced up the slope of the roof, where the turbine is ready and waiting. Mr. Chiras, and people like him may be the reason why VAWT's are not more prevalent. (The preceding was unsupported conjecture, just like the article.)

Willy Scanlon
3/22/2009 5:31:14 PM
I think that this article is a little one-sided. I live in a tropical part of the world(South Vietnam) where we have constant trade winds from the South China Sea and very little ground clutter. VWT's work just fine here. They also work fine in areas along the shoreline or on tropical islands where there are constant prevailing winds. My house has 3 of them at the crest of the roof and are made from light weight tin with graphite rods(heat resistant from friction generated) to the alternators. These VMT's provide almost 80% of the electricity that we use. The remainder is provided by a solar panel. They are also more cost effective than a HWT and less of an eyesore to my neighbors,can work in limited space,do not interfere with my fruit trees, not to mention the noise levels of HWT's. I think that the author of this article needs to look "outside the box" in America once in a while.

B Knight
3/21/2009 1:00:07 PM
I must say that this article is not up to Mother Earth standards. It would appear to express one person's opinion, without supporting facts. Dan has a vested interest in pushing HAWT's as he sells hands-on courses, on how to build HAWT from scratch. Let me add, that the HAWT's that Dan will show you how to build, are great wind turbines and well worth learning to make yourself. They are also shown at http://www.otherpower.com/ . More DIY models can be found at: HAWT- http://www.greenterrafirma.com/DIY_Wind_Turbine.html VAWT- http://www.greenterrafirma.com/vawt-designs.html Wild comments such as "they’ve failed miserably" and off topic examples such as "mount a solar electric module inside your garage", are used in publicity announcements, not in factual articles. VAWT's do have a place, alongside HAWT's. Hopefully Mother Earth can be a bit more objective next time both designs are compared.

Brian_26
3/21/2009 11:58:50 AM
This pro HAWT article is full of misinformation. VAT's are more efficient and reliable. Not to mention the expense of maintaining these (commercial scale) HAWT's is not even mentioned. If your referring to eggbeaters, you are 35 years behind the power curve, improvements in VAT designs and bearing life are far superior. Why all VAT designs are lumped into a single category as "failures" is nonsense. Ed Begley Jr chose a VAT turbine design for his own home, what's up with the VAT bashing. Go look at TMA Wind and educate yourself. Brian

DB_3
3/21/2009 11:38:19 AM
Did you draft your story in your 1 bedroom shack that you call your headquarters or the single-wide out back that is your future classroom for the thousands (yeah right) that follow your lessons? I wouldn't be so sure that Ed Begley Jr considers you a friend or ally. Dan, which HAWT do you push to your students?

George Works
3/21/2009 5:06:43 AM
Horizontal axis wind turbines are quite noisy whereas vertical axis turbines are not. I've installed two wind turbines and lived next to them, and I can personally vouch for this. Regarding efficiency, the important points to a buyer are 1) what does the turbine cost (including installation), and 2) how much power does it deliver? Efficiency per swept area is really only important to engineers. Vertical axis turbines seem to be quite competitive. I live on an island in the hurricane belt and must be able to take down and re-install a wind turbine myself. Some vertical axis turbines make this quick and easy, as they are hinged at the base for this purpose. It's not so easy with a horizontal axis turbine.

gloria_13
3/20/2009 10:01:49 PM
all i need to know is where within the us i can buy and have installed a vawt.

Gary Deal
3/20/2009 9:06:40 PM
Dear Sir: You need to go to this site http://www.windstuffnow.com/main/formulas.htm. This man has a large amount of information on both HAWT and VAWT system. I'm in the act of making a VAWT system using his prints. He is very helpfull in building the generator to making and winding your own alternator. He seem to like helping anyone with a wind system. Thank You Gary Deal readers@scrtc.com

Will Brooke
3/20/2009 7:21:16 PM
... your points about turbulence are great; turbulent flow carries less energy, obstructions (like buildings or trees or mountains) tend to create a "cone-like" shadow of turbulence ~1.5 times the height of the object and for a distance of between 4 and 7 times the obstructions height (depending (mostly) on wind velocity)... while VAWT's _CAN_ be used in turbulent flow, that is not their ideal environment. laminar flow has more extractable energy. placing a VAWT up high, in unobstructed laminar flow area, will provide it with the same potential energy as a HAWT in the same environment. while traditional vawts that we normally think of, are often seen operating at ground level, that is far from the only design, or the only implementation method. VAWTs are useful (but again, not ideal) because they CAN be used in turbulent flow areas. if you do not have the capacity, or ability to build a tower, or access laminar flow, then a turbulent-flow restricted, ground-level VAWT is a reasonable alternative. statements like "they are less efficient or reliable than hawt's"... this is based on what? which VAWT design? what type of mounting and flow environment. Were they placed in areas where HAWT's were completely impractical? likely, are those ideal situations. no. do they work, even at less than peak efficiency? yes. so what is the problem? this article, while perhaps well intentioned, appears to be poorly researched and presented. At the very least, please provide a list of references. even better - admit that you are comparing apples and oranges (and please acknowledge all the different varieties in each family, they have their appropriate applications. VAWT's would be completely impractical in the locations off scotland where the large UK windfarms exist, that is a great location and area for mega-HAWT's)

Will Brooke
3/20/2009 7:19:49 PM
THERE IS NO SUCH THING AS CENTRIFUGAL FORCE. Ask any engineer. (what you 'feel' when you go around a sharp corner in a car (as an example) is the centrepital acceleration of the car pushing against you. The centrepital acceleration vector is aimed at the center of the circle/curve; you (the occupant) are still undergoing linear acceleartion in the direction you were last traveling (straight ahead) until the door started exerting its force on you. So the force isnt you pushing against the door (outward), it is the door pushing against you (inward) The same is true in a wind turbine, VAWT or HAWT. BOTH systems undergo the SAME forces. The force differences are dependent upon the total area of the wings (blades). While the traditional savoinus (egbeater) blades have very large diameter in the center, that is not the only design of VAWT available or proven. (and again, the magic of math shows us that as the radius of the blades decreas, towards the top or bottom of an eggbeater vawt, the forces they undergo correspondingly drop. next, your complaint about wings twisting and bending -- again, the forces undergone by a blade in EITHER system are calculable and can (and should) be properly designed for. the forces in BOTH systems are similar. so do NOT assume that "HAWT's have less stresses upon them" that is simply false. Further, ther terms of reference for statements like "more energy for a given area" is not clearly defined and in general, is misleading. Again, this is generally compared using traditional eggbeater VAWt's with guy wire supports, and the wasted space from guy wires count against the footprint. A high aspect-ratio micro-VAWT extracts a lot of energy for its footprint, can easily be mounted (as all wind turbines should be) on a tower to sit in a stream of laminar flow. A mega-HAWT with a 500' wingspan needs pi*250'^2 area to operate (so that it can turn into any direction of wind) your points







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