We get bombarded here with questions about short towers:

  • I built your turbine, but they won’t let me put it up on a tall tower, is it OK to put it up on a 20 foot tower in the garden behind the house?
  • So and So’s website said that their wind turbine design works better than yours right on the ground!
  • Such and Such wind turbine design “eats up turbulence for lunch,” it says so on their website and since it’s on the internet it must be true! And some of the text in their website blinks!
  • “They” (or “everyone”) say that VAWTs (vertical axis wind turbines) work better on short towers and in turbulence than HAWTs (HAWTs are what we build in our book).
  • “They” say that if I buy their turbine, I can put it on my roof because the wind speed increases going over the rooftop, just like an airfoil. Why doesn’t your turbine do this?
  • There’s a very reputable big company that sells a grid tie wind turbine on a 30 foot fiberglass tilt up tower, and it’s only a 30 foot tower. They obviously know what they are doing, so I’m going to buy one and line my bird cage with pages from your book. Thanks for wasting my $39.95. (OK, we made that one up, but we are sure we’ll be getting emails like that soon).

It’s all Hokum! Hogwash! People are making this “data” up for good reason–most folks, when considering a wind turbine, do not want to or are not allowed to build tall towers. And that really puts a big crimp in wind turbine sales. There’s no guarantee from the manufacturer of energy output per month with any wind turbine, it depends on your wind regime. And once you sign on the dotted line, all you can do is scratch your head a year later and wonder why your turbine is putting out only a tenth the energy per month that the website and friendly sales rep said it would. Frankly, the authors spend as much time convincing folks that wind power is NOT right for them as we do helping folks with wind turbine questions.

The only published, scientific test results out there completely disprove all of this nonsense about rooftop turbines and short towers. Look at it this way — the earth’s surface causes “friction” to the wind. This has been extensively field tested and computer modeled for decades now. Friction slows the wind down. And the power available to you in the wind goes up by a factor of 8 when you double the wind speed!

Here are a few of those articles, from reputable wind power scientists:

Hugh Piggott’s measurement of urban wind speed over a roof top at Wind Speed Measurement in the City.

Comments by Hugh Piggott “Rooftop wind turbines are a load of nonsense”

Rooftop Turbines: Rooftop Mounting and Building Integration of Wind Turbines
By Paul Gipe

The case (or not) for Roof Mounted Wind Turbines by Nick Martin

Andy Mahoney’s Rooftop Mounting Failure at http://navitron.org.uk/forum/index.php?topic=942.0

Some test data from the authors:

Co-author Dan F and Otherpower.com Stator Specialist Rich C fly the exact same little wind turbine, the 7-footer that’s described in detail in Homebrew Wind Power. We both really enjoy this little machine.

We had no way to easily make this a scientific test…but we DID measure kilowatt-hours per month from identical turbines at sites only 1/2 mile away, during both high-wind and low-wind months of the year.

  • RIch’s turbine was on a 50 foot tower, with hub height about 10 feet above the nearest tree within 300 feet. However, the hillside stretches up above his turbine, so there was turbulence caused by that. It was a ’so-so’ location by normal standards (which say your turbine must be 30 feet above anything within 300 feet in any direction) but far less obstructed than DanF’s, below.
  • Dan F’s turbine was on a lattice tower, 40 feet in the air, right next to his house. The turbine is above the house roof peak by about 10 feet. There are numerous trees in the area taller than this within 100 feet. DanF broke all the tall tower rules he talked about in Homebrew Wind Power because he didn’t listen to his own advice wanted to prove a point about the importance of tall towers.

During the same period of 3 months, Rich’s identical 7-foot wind turbine made over 10 times the amount of energy per month (in kilowatt-hours, the only really important measurement) because of Rich’s fairly OK tower site, compared to DanF’s bad tower site.

Ten times the energy……

What were you THINKING, DanF?

(authors note — DanF was thinking that it would be cool to have an easily accessible tower top where he could test different small turbines and swap them out with little effort. But that’s not much use when the tower is not tall enough)