ASK THE EXPERTS: VAWT Commentary

Beginner
Siting a VAWT (or any wind turbine) on a short tower, in low-speed or turbulent winds, is a recipe for wasted money and disappointment.

I am a longtime subscriber and wind power, solar thermal, and solar-electric enthusiast. My rezoning application for a 6 kW horizontal-axis wind turbine (HAWT) was denied due to height restrictions in my semi-rural development. If I want a wind turbine, it needs to be mounted on a shorter tower. Turbulence is a problem here, so I have decided to try a vertical-axis wind turbine (VAWT). Using this will not require submitting a rezoning application.

Is there a viable 5 to 10 kW rated VAWT that has been installed in the United States in any appreciable volume in the last few years? I would consider purchasing a foreign product as long as it has a good track record and decent warranty.

Hans Sinkovec • Jefferson County, Colorado

A good measure of a wind turbine’s worth is its annual energy output (AEO), defined as kWh of energy per year. This number depends on the annual mean wind speed, and the turbine’s size (swept area) and efficiency. The standard “reference” site has a mean wind speed of 5 meters per second (11 mph). In most places where people live, you would need a tall tower to access this mean wind speed. Wind energy around buildings and trees will be much lower, and the wind is turbulent.

VAWT products are characterized by a high degree of marketing hype, and a high rate of failure. High-speed VAWTs have problems with startup and blade fatigue issues. Low-speed VAWTs have terrible efficiency. Comparing the kWh per year of energy produced on sites with the reference annual average wind speed of 5 m/s (11 mph), HAWTs produce 344 kWh per square meter, whereas VAWTs produce only 201 kWh—58% as much for their size.

Just as it’s not a good idea to put a HAWT on a windy and turbulent site, because of the loads this puts on the blades, a VAWT is equally likely to fail on any windy site for the same reason. VAWTs are often sited too low to experience useful wind, so they do not fail.

Before you part with your money, find someone who already owns a VAWT and can show you measurement data proving that it does what it claims to do. Reliable VAWTs are rare, costly, and unproductive, and using a VAWT at low height is not a solution. More likely the best solution will be to install a PV system instead. A study published in the Journal of Clean Energy Technologies based on typical European solar irradiance concludes that PV energy is less costly than Darrieus-type VAWT energy in annual mean wind speeds of less than 7 m/s (15 mph) or Savonius-type turbines in wind speeds less than 10 m/s (22 mph).

Hugh Piggott • Scoraig, Scotland

Comments (6)

spynage's picture

What about VAWT's with adjustable pitch blades though. Are there any commercialy available? They seem like a really good idea for lower wind speeds. There are a few examples on youtube.

Michael Welch's picture
One problem is that there is too little energy in low wind speeds to bother spending thousands of dollars to capture. My recommendation: either put robust wind turbines high up into faster, non-turbulent air, or stick with a PV system.
August Goers's picture

We (Luminalt) designed and installed a vertical axis turbine test site in San Francisco completed in 2012 and recently updated with new turbines in 2017. Long story short, the turbines produced VERY poorly and failed frequently. Luckily, this was just a test site used to gather data. If you want real energy production, focus on PV. Here is a link to the dashboard where you can see per-turbine performance: http://frogdashboard.com/crissy/det...

Michael Welch's picture
Interesting, August. Average wind speed of 8? mph produced 16 kWh so far this year (though some of the turbines also have PV modules on them).
August Goers's picture

Yes, I think most of that production was from the solar cells installed around the perimeter of the Omniflow turbines. There is currently quite a bit of high resolution wind and production data being collected which should eventually make it into an official report provided by the Hawaii Natural Energy Institute. Here is more information on the original 5 turbines: https://www.hnei.hawaii.edu/project...

Frank Heller's picture

Over a decade ago, I did a wind assessement for a coop association on Portland's waterfront adjacent to Dimillo's floating restaurant.

I recommended because of the daily fluctuations in wind direction and velocity a line of VAXT's would produce some of the power they wanted to heat, right heat, an underground parking garage.

Time goes on; years later we go to Dimillo's and there is a large--20' high, VAXT off to the side of the ramp to the rest.....very near where the photo was taken. There is a sign, it's still in operation, unclear who is maintaining it and what its output is. But if you call.....better yet eat there, they may be able to help you .

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