Re: Low speed turbine performance [downwind]
The induction motor approach sounds like a good avenue to pursue.
I'd be real careful designing a downwind machine. I found in years of research with the SuperTwin(TM), which has two (2) rotors, one upwind, and one downwind, that if your downwind rotor is less than one rotor radius of the tower, you can experience extreme buffeting that could threaten to rip the machine apart. I was surprised when we finally started experimenting with various distances from the tower and found how strong the wake effect really is - VERY.
Note: The Skystream has curved blades so they don't hit the tower wake all at once, and they are significantly spaced away from the tower already.
Like every other aerodynamic interaction in wind energy, the tower wake is invisible, so it is tempting to pretend it is not there. Believe me, it IS there.
--- In firstname.lastname@example.org, "Jarrett Johnson" <hjjohnson@...> wrote:
> Thanks Michel! This is pretty much why I was asking.. In simple terms
> I'd rather have 10kw of power generated for ~ 4-5000hrs a year vs 20kw
> only ~1000hrs a year. The blade pitch system [I have a couple different
> routes I can take] is such that w/ a loss of power the blades will
> default to a feathered condition. I'm planning on using an induction
> style generating system via a gearbox and 3phz motor. I'm currently
> planning a down wind turbine so wind alignment isn't an issue in the
> event of a power loss and feathering of the blades. That in conjuction
> w/ a mechanical brake on the motor should take care of the the safety
> sides of things [in the broad strokes anyway].
> Data sensing tower will be up in the next couple weeks [tower is
> there, foundation is in, anchors are in, data collection system has
> arrived.. the time/labour to erect it all is the only thing missing!]
> which will confirm [or not] what the wind maps are saying for my
> region.. I'm expecting my annual mean wind to be 5.7m/s at 30m on a
> Weibull K=1.88 & Weibull A= 6.88m/s, we'll see if that works out w/
> the real data or not.
> I've been working on this idea for more than 15yrs so it's kinda nice
> to start actually 'going' somewhere with it!.
> Thanks again for the reply!
> Jarrett Johnson
> On Thu, 30 Aug 2012 09:53:43 +0200, Michel Stievenart wrote:
> I have some examples of a few machines designed by the French
> company Aerowatt (1960-1980)
> They were of the pitch-stall governing type and rated for two
> windspeeds : 5 and 7 m/s
> The governing system was very efficient but a bit noisy and gave a
> perfectly constant power above the rated speed.
> For an example, for the same diameter : 3.2 m , the 200 FP5 was rated
> at 200W@5m/s and the 300 FP7 : 300W@7m/s
> For a 5m diameter , there was a 1100 FP7 : 1100W@7m/s
> They were used with success on offshore lighthouses.
> Of course the power is not very high but you had a much more reliable
> and usable machine.
> IMO active pitch (feathering) should be a great improvement if the
> pitch system control is highly reliable and seconded by an emergency
> safety mechanical device.
> De : email@example.com
> [mailto:firstname.lastname@example.org] De la part de jerryflyguy
> EnvoyÃ© : mercredi 29 aoÃ»t 2012 00:14
> Ã : email@example.com
> Objet : [s-w-h] Low speed turbine performance [reposted]
> I've been pondering something and figured where/who better to ask
> that the small wind list.
> Has anyone done or seen any data on low speed turbine performance on a
> active pitched turbine? I'm looking for cost/return graphs as far as
> the theoretical limits of how low a target wind speed should be before
> the efficiency of the system is compromised by it's installed cost. The
> key is actively pitched [actively governed speed whether it's
> electronic or Nando's Torque pitched system] such that in higher winds
> the generator is not overdriven to the extent of burning it out etc. In
> theory this would also allow a simpler tower structure because it
> wouldn't need to resist the full load of the high winds because the
> blades could pitch out and reduce the load on the tower [or said
> another way; keep the loads on the tower constant through the range of
> wind speeds].
> Is it possible to build a turbine that will generate rated power at
> 7m/s? Would it be economical? 10m/s? At what wind speed [starting from
> the low speed end] does this cost/return curve cross over into a
> turbine which is efficient enough to be practical vs it's installed
> J. Johnson [oh there's lots more of these 'curious' thoughts that
> rattle around 'me head.. I try to keep them locked up as much but, once
> in a while one gets out :) ]
> [Non-text portions of this message have been removed]
- How much do we know about the house of wind generators? How well do we know
"all" the walls? Will dimples cause a non-stir? :) When do we decide the
wall we have previously defined should be blown down due to advances in
technology and technique?
We stay where we are if we do not reach for something new. History is a
teacher, but it can also be a crutch. Where do you stand?
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