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The Value of a VAWT - Page 2

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Posted by Josepi on January 14, 2010, 3:18 pm
 


Better magnets will improve things, significantly. Expensive though.


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
the
roof enhancing operation, instead of impeding it by causing
turbulence.

Not as much problem with it going excessively fast, either. No pointy
blades flying into a neighbor's roof if something gets loose. No
problem
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
with
an appropriate generator interface.

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

Comments?



Posted by Swims with Dolphins on January 15, 2010, 1:50 am
 


I'm a bit concerned about having a huge stator with a central axis.
Even a little bit of flex would cause a magnet/stator crash.  Suppose if
you could put wheels along the outer edge to prevent such a crash it
would work.

The other kicker is that there is just so little energy to harvest in
low wind speeds.  Its that cube function aspect.  Whats viable in a
20mph wind generates 1/8th the power in a 10mph wind.  Think about that
in terms of payback:  If a unit paid for itself in 5 years in a 20mph
wind, it would take 40 years in a 10mph year...

Michael B wrote:


Posted by Josepi on January 15, 2010, 2:38 am
 

I doubt that bearings are a huge issue. A longer, stronger shaft and two
good bearings would stabilize the collector.

The low RPM can be handled by gearing or step-up pulleys to the generator,
off to the side of the unit.

Efficiency looks very poor for the size, compared to horizontal units, but
the tradeoff is the height not required, tolerance for gusts and
serviceability.

Self regulation of speeds is another plus for VAWT units. Propeller blade
units get out of control quite easily.


I'm a bit concerned about having a huge stator with a central axis.
Even a little bit of flex would cause a magnet/stator crash.  Suppose if
you could put wheels along the outer edge to prevent such a crash it
would work.

The other kicker is that there is just so little energy to harvest in
low wind speeds.  Its that cube function aspect.  Whats viable in a
20mph wind generates 1/8th the power in a 10mph wind.  Think about that
in terms of payback:  If a unit paid for itself in 5 years in a 20mph
wind, it would take 40 years in a 10mph year...

Michael B wrote:


Posted by Michael B on January 16, 2010, 4:54 am
 

Do you know how to cut a 4 ft plywood circle
with a tablesaw? The magets can be in holes
in the plywood, covered with portions of microwave
oven transformer. Yes, wheels to prevent wobble.
Two magnet circles for axial flux operation.

wrote:


Posted by Josepi on January 15, 2010, 11:20 pm
 

Here is one you may like to drool over. Made in Canada, apparently. No
prices, I can see.

http://www.ocipenergy.com/downloads/Fact%20sheet%20-%20CFE%20V3.5%20v1.1%20Sep%2009.pdf


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
the
roof enhancing operation, instead of impeding it by causing
turbulence.

Not as much problem with it going excessively fast, either. No pointy
blades flying into a neighbor's roof if something gets loose. No
problem
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
with
an appropriate generator interface.

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

Comments?



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