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The Value of a VAWT

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Posted by Michael B on January 14, 2010, 2:24 am

Traditionally, horizontal axis generators have been used because
there is such convenient spinoff from other technologies. And it's
a lot handier to be able to go with generators that are already set
up to do the job. Higher RPM, higher the output.

But a big problem is in extracting anything from wind speeds less
than about 6 MPH. So if you want things to move, you pretty much
have to go with a drag-style unit, such as a Savonius style.

Since it won't exceed the prevailing wind speed, its generator has
to be optimized for low RPM.

But if you aren't obliged to have that generator on a pole, behind a
prop, you have a lot more latitude, but you pretty much have to
build the generator yourself.

One of the biggest aspects is how many coils of wire a magnet is
going to pass in a revolution. 10 coils, 15 coils, whatever. But how
about a vertical unit, with a 4 ft diameter base? A really large
number of coils being passed, it's not up there 40 feet in the air,
and it doesn't care which direction the wind is coming from, or how
much turbulence it contains. There's a unit getting ready to go on
the market that has a 6 ft diameter face, with its coils in the outer
perimeter. Put it at the top of a roof, and get a "roof effect" with
roof enhancing operation, instead of impeding it by causing

Not as much problem with it going excessively fast, either. No pointy
blades flying into a neighbor's roof if something gets loose. No
pulling maintenance on the generator, easy to get to the turbine. No
steel cables and excessively long ladders, or cranking it up and down.

I've got 80 microwave magnets that say that a VAWT is more practical
for the urban dweller, and likely others as well, even though the gold
standard for high end of efficiency is better for the horizontal unit.
I feel
that pragmatics are in favor of the vertical, IF the user can come up
an appropriate generator interface.

No, I've not built the big one, but the practice one worked very well.
didn't have a generator attached, so I was able to call it kinetic
yard art.


Posted by vaughn on January 14, 2010, 2:34 am

I suppose a 6' vertical axis drag-type turbine would have fairly high torque
coupled with low RPM.  Why not do the obvious thing and use a high efficiency
chain drive to increase the rpm of a more conventional generator?.


Posted by Michael B on January 14, 2010, 2:41 am

High efficiency still means some loss, but so what?
Big beal if it loses a little, it can sit on the workshop
table with the batteries underneath. The practical utility
has to have some value.
And my "practice" turbine cost barely $0.


Posted by vaughn on January 14, 2010, 12:55 pm

Since every energy conversion involves some loss, "high efficiency" is the best
we can hope for.  Chances are, (though exceptions may exist) any commercially
built generator will be better than any garage-built generator.


Posted by Jim Wilkins on January 14, 2010, 1:53 pm


"Better" is elusive within the constraints of time, space, cost and
acceptance. Whatever I build is within my ability to repair. Much
commercial equipment is designed assuming the owner won't maintain it,
for example "lubed for life" driveshaft U joints without grease
fittings. When the grease is gone their life ends. (Did you assume it
meant yours??)

Bearings are much easier to press into a recess than to pull out,
unless the machinist takes extra time to provide access. But why make
it easy to fix when the owner has been conditioned to buy a new one


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