Wind generator design options?

[fluxable]

I live in an area with low wind (average wind speed is between 3 and 4 m/s) and in a residential area in a small town. Like many areas, there are days when the wind can blow well in excess of 15 m/s for hours or even occasionally days at a time. So, I've decided on a vertical turbine, which should work better and is safer in a residential area. I'm aware that vertical generators are not as efficient as horizontal ones and that the wind above ones rooftop is likely turbulent and diminished from up higher. So wind options don't look good, however, I am still interested in harnessing some power from the wind.

To maximize power from the turbine, I am planning to build a large diameter rotor and deflect extra wind into the turbine with baffles in an angled triangular arrangement.I haven't decided on the actual size and potential power output as of yet, but hoping for 1 kw or more output at full power. That may be a stretch?

For the generator design, I was thinking of using one rotor, and installing two stators on either side of the rotor. One stator would be wired to maximize power at very low speed, and the other to maximize power at mid level and higher speeds. This could be done by using more windings and higher gauge wire with more turns on the low speed producing stator, and opposite for the high speed stator. One could then automatically switch between the windings using relays, depending on the rotor speed. I'm aware of a design that switches winding configurations on one stator, also depending on speed of the rotor. I was also thinking of using a large(r) diameter rotor, to help maximize power production at lower speeds, providing the turbine has sufficient surface area and thus torque to maintain the rotation velocity.

I was just curious if this is feasible and if any others have made similar attempts? Or perhaps I'm just barking up the wrong tree, given the low wind potential in my circumstance? Any thoughts would be appreciated, thanks!

[Rover]

In a residential area... how high up to you plan on making the turbine? and how large a wind swept area (diameter of blades and hub...ok) ?  

I live in an residential area with extremely variable wind, from nothing to 30+ mph. Typically not an even blow.

I'm at 30 feet need to be at 60 ft (or more) , due to turbulence from buildings and trees, but can't due to rules. (I still see how much I can get and work with it)

Although I have seen very high outputs, they are sporatic.

[Rover]

ok vertical...

no idea thought HAWT until I re- read

[bzrqmy]

There are lots of stories about VAWTS here on the site.  Spend a lot of time reading through them, like a couple weeks.  If you are set on a VAWT for some reason and enjoy fabrication, it could be fun.  As for output, you will be pretty dissapointed when we tell you that you can probably only expect 50-100 watts out of one of these, about 10-20 times less than your goal.  Seems like there is some prize money to be collected for someone that makes a sucessful VAWT, I forget the rules.  Just use that google search link up to the left.  

There are people getting a couple hunderd watts out of 4' turbines.  If you just don't have the room to do it safely, maybe a pedal powered generator or some solar.

Whatever you decide, good luck and keep us posted.

[fluxable]

I was thinking of making it fairly large, around 10 feet in diameter, although it may not need to be quite as big if wind can be funneled in with baffles? I think it would need to be at least this size if planning to generate over 1000 watts. I'm aware of the inefficiencies  and poor performance of the smaller vertical units. One of the inherent problems is that the orientation to the wind of these units is not ideal, as in a horizontal configuration. I believe this can be improved through proper placement of baffles around the unit, which could funnel the wind around the turbine more effectively. I have seen an example of a large scale unit where the company claims much higher efficiencies?

But what I'm really interested in knowing is, the possibility of getting better power efficiency at various wind speeds using a double stator, as mentioned above. Is it possible to generate power in light winds with a system like this. In other words, to obtain a much lower wind start up speed where some energy can be produced when the winds are light. I'm aware this would require a large turbine to capture as much as you can in order to generate a high torque, but at a slow revolution rate. And then convert this motion to energy with a large(r) diameter rotor, to maximize output at this slower speed.

 I'm award of the law of physics, and at low wind speeds, there is only so much energy available, and reason for the large diameter turbine!

[CmeBREW]

Hello Fluxable.

    What you decribe is the typical difficult situation many have and many ask about here. Low wind, Residential area, etc.  

I hate to sound negetive, but have to agree with BzrQmy.  There probably is not much you can do with wind power in that kind of Residential situation, unless you can put a windmill high in the air. But the Neihbors will see it unfortunetly. There is almost no wind at ground level in a Residential area since there are buildings, fences, and trees everywhere. Unless you have a decent clearing in your yard.

It would probably be best to invest the initial moneyies in a small QUALITY Solar panel and the other RE-items for a small starter system. That would produce the Most Average Watthours in that kind of situation.  And then you could perhaps mess around making various small mills (Hawts and Vawts) more as a hobby than serious power.

Vawts are much more difficult to make than a small Hawt from my experience. Your power expectations need to come WAY down-- to more like 20watts (6 sq.ft Vawt)in good wind gust if you make a good design.  A small Hawt is a lot more forgiving in many respects. But Vawts are fun to experiment with for me.  I am still working on a new better Vawt right now AND a small Hawt, AND an improved Pedgen. Everything is fun and good.

   "I was thinking of using one rotor, and installing two stators on either side of the rotor. One stator would be wired to maximize power at very low speed, and the other to maximize power at mid level and higher speeds".

This sounds very complex. It seems to me there would be a problem with this in that a stator on each side of the ONE magnet rotor would mean the 'Magnetic circuit' would be totally incomplete and therefore would not work good at all.

Of course if you had two steel discs turning WITH the center magnet rotor-- behind each Stator, it might work, but seems unnessarily difficult to me.

I would think TWO sets of coils over-lapping in the SAME (ONE)Stator and the dual Rotor design might be easier but still very difficult to do the auto-switching.  I like the simple sound of just gearing an Alternator OR DC motor myself. But thats just me.  But making a small Hawt is always easiest.

Hope you have some success whatever you choose to do. Look forward to seeing it.

[ChrisOlson]

The swept area of a VAWT is the diameter of the rotor times the height of the blades.  So a 10' VAWT with 5' high blades will have a swept area of 50 square feet, as an example.  This is equivalent to about an 8' diameter HAWT.  The formula for the amount of power you can get from the wind is:

Watts / ( .00508 x windspeed^3 x efficiency ) = (swept area)

But with a VAWT there's a caveat - only half the swept area is effective unless you build a lift/drag wing.  And with convergence vanes on a VAWT you're only building a pure drag turbine.

In short, if you want 1 kW in the wind speeds you're talking about it's going to have to quite a bit bigger than 10' x 5'

--

Chris

[fluxable]

Thanks so much for the feedback everyone! I might just start with a small VAWT to begin with. I love experimenting with different designs, and who knows, what you may come up with. The one other idea I had with VAWT's is to deflect the wind that is not beneficial on the one side of one unit, to another one, and so on. Of course this would be more practical with smaller units. But it would add to the complexity and require use of a vane to control the direction of deflection, dependent on wind direction. Another interesting design I saw was to use a large vertical cylinder to deflect wind to a stack of small HAWT's on either side.

I realize that building a turbine above my roof in an urban environment will not be a big energy producer, but it will produce some power when there's some wind. I'm located at the edge of a farmers field on one side, and it's also quite open on the windward side (ie west) as well, so when the wind does blow here, it blows through my yard very strong. The wind would even be better up on the roof.

As for using 2 stators, the rotor could incorporate the magnets so they sit close to flush on both sides. This way you could have separate stators on each side.

As for the complexity of the switching circuit, it could be done quite simply. Just need a speed detection circuit or could use the output voltage, and compare with a reference, which is amplified and used to trigger a relay. A simple circuit really.

[ChrisOlson]

I'm not sure about the dual stator thing either.  The typical VAWT, while it don't turn all that fast, does develop quite a bit of torque if it has 10' diameter or so.  Why not just use a step-up drive to run the generator faster than the turbine?  The wing tip speed on a VAWT usually runs about 80% of the wind speed if you have it driving a load of some sort.

Just use this formula to figure it out for a starting point:

Windspeed x 88 / ( diameter x 3.14) x 0.8 = RPM

With a VAWT that rotational speed is going to be very low.  Take a 10' diameter unit in a 10 mph wind - it'll run at about 35 rpm.  So design your generator for a 140 rpm cut-in, which is reasonable with a 12 pole alternator with 9 coils and about 50 turns of wire in the coils.  Then drive it with a .25:1 overdrive.  You can use a roller chain and sprockets, cogged belt, a gearbox of some sort, etc. to drive the generator.

This is just an example for a cut-in speed of 10 mph with a 10' VAWT.  You can design it accordingly if you want to try to get it to cut in sooner.  But I think the dual stator thing sounds like a nightmare in the making.

--

Chris

[Kwazai]

I think, except for probably february and march, that you are in a 'yard art' area rather than a power producing one. My situation is similar. this one is about 5' diameter hawt (drag type sailmill).

http://www.youtube.com/watch?v=x1HWPSSQU4w

L8r

Mike

[wooferhound]

 As soon as you put a huge shroud on a VAWT then you will realize that you should have gone with an HAWT since they are both tracking the wind direction anyway. We have talked about putting a shroud or diffuser on a wind turbine many times...

http://www.fieldlines.com/story/2003/6/17/73839/3388

http://www.fieldlines.com/story/2007/7/13/221748/030

http://www.fieldlines.com/story/2005/7/11/21517/7456

http://www.fieldlines.com/story/2005/7/11/21517/7456

http://www.fieldlines.com/story/2003/11/22/7365/5340

http://www.fieldlines.com/story/2006/10/10/232638/13

You need to throw away the dual stator idea right now. The generator for a VAWT needs to be much stronger because of the slow RPMs. Building a dual stator generator like you describe is giving each stator half the magnet power in a situation where you need all that magnetism focused on 1 set of coils to get enough power in the first place. instead use small gearing (1:2 , 1:4) or transformers to step up the gennies voltage.

I think you are operating under a misconception. people think that since they have turbulent nondirectional wind in their neighborhood backyard, that they should use a VAWT to utilize that kind of wind power. But the fact is that, both VAWT and HAWT need straightline wind to work with any efficiency at all, so that means going UP to where the wind really is.

If you have a house next to yours, then check the wind funneling between the two houses, it might be enough to surprise you.

 

[fluxable]

I've seen many others design and build their own generators. It doesn't look difficult and to add an extra stator is IMO simpler than putting in a gearbox and drive system which will add to the losses and require additional maintenance. Most generators have one speed in which they run the most efficiently. By changing the electrical characteristics of the generator, you can alter that sweet spot (ie a different speed) without having to put in a complex transmission to achieve the same result. Building a generator is not that difficult and I see it as a fun and challenging project actually.

[fluxable]

My idea to use a dual stator would only use one stator at a time. Each stator tuned to maximize performance at different speeds. But I think it may be more efficient to also use 2 rotors as well. I have looked into to using both sides of a rotor and the 2 rotor option looks like it would perform better from research I have recently done.

As for the shroud or diffuser you mention, there is a commercial large scale design I have seen of a VAWT that uses this technique, and they claim a much higher increase in efficiency. Mind you, the walls use to deflect the wind into the turbine are quite large. Google it and you will see what I mean.

Yes, I do get plenty of wind on both sides of my house when it blows. I will look into that as well. The land here is very flat and not many trees in the immediate vicinity, and thus the wind blows through my yard quite intensely when present. I don't have high expectations, but it would be great to generate what power you can. Solar is not the best option either, as it's very expensive to buy the panels, and there is only about 6 or 7 hours of low angle sun here in winter, when power is needed the most.

 I have also been looking at using wood pellets to generated both heat and electricity. There is a furnace made in Europe that does this using a stirling engine and linear generator. I believe there is another unit made in the US as well.

[fluxable]

Looks good, lol! Yes it may be a contest to see who's looks the best, ha.

[ChrisOlson]

What I see as a potential problem with what you are talking about is that you're going to have to use steel or iron cores in the stators to make maximum use of the flux, and you're going to have to have the magnets exposed on both sides, i.e. you can't just put them on a steel plate.  The complexity involved with building steel/iron core stators (and getting them right the first time), plus building a complex generator rotor where the magnets are exposed on both sides far outweighs the simplicity of using a step-up drive to run the generator.

The most efficient axial flux generator will have a stator sandwiched between two PM rotors, not a PM rotor sandwiched between two stators.

It don't really matter how you try to design it with two stators, you're just simply NOT going to get any power out of it at the speeds that a VAWT runs at if it's direct drive.  I did some quick calculations and if you want a cut-in speed at around 10 mph wind speed and 35 rpm on a 10' VAWT, and assuming you build a three-phase, 12 pole generator with 9 coils - three per phase, you're looking at 194 turns of wire in the coils to reach an open voltage of 15.0 VAC @ 35 rpm.  It's just not practical.

If you're convinced that it absolutely HAS to be direct drive, then I'd start thinking about a large diameter (like having the coils arranged in a 2' circle) radial flux generator and forget building axial flux stator plates.  It's the only way you'll get any power out of it.

--

Chris

[fluxable]

I'm now aware of the inefficiency of using both sides of the magnets (of a rotor) with stator on either side. And thanks Chris for reinforcing that decision. Better option is to use separate pairs of rotor and stator. I'm still thinking direct drive and had a large diameter in mind. I looked at the option of building a radial flux generator, and looks far too complicated to build. The axial flux generator is much simpler in comparison, and should have a higher output at lower speeds if the diameter of the rotors and stators is large.

The real issue I'm trying to get around is to maximize efficiency at different speeds. You can build a generator that has a very low cut in speed and begins generating some power in lighter winds. Problem is this generator will not be nearly as efficient and produce as much when winds are much higher. Same problem if you gear up a generator to run faster at low speeds. If you get higher wind speeds, the performance of the generator will suffer. And the same thing happens for the opposite, if you build a generator to work more efficiently in higher wind speeds.  

I realize that putting in 2 rotors and 2 stators will result in a slight drop in efficiency. The question is " do you not gain more by having both a low speed generator and higher speed generator in one package, ie. 2 stators and 2 rotors and select the most appropriate one for the current wind speed."

[fluxable]

Here is an example of a commercial VAWT that uses a diffuser (ie walls that deflect the wind), and they are claiming a very high efficiency of between 40 and 45%.

http://www.treehugger.com/files/2005/11/ultra-effective.php

They go on to say that the main advantage is lower maintenance costs due to ground level access of the generator, gears, etc... They also say it will produce power at higher wind speeds than typical commercial HAWTs. It may have a high efficiency, but the one disadvantage I see is that it is capturing wind closer to the ground, where there is less wind. May work more effectively in certain geographical locations (ie a pass), where the wind will be funneled closer to the ground. They also say that turbulence is less of an issue with this arrangement.

Has anyone else created a similar design and tested it? It sounds interesting?

[wooferhound]

This VAWT works a lot like you are describing

http://www.fieldlines.com/story/2007/12/12/9444/1180

[fluxable]

Interesting...

[ChrisOlson]

Well, I think you somewhat misunderstand the generator part of it.  You don't need to optimize by building two different generators into it.  Just build one that's matched to the turbine's power output and it will work fine starting at cut-in, and all the way to its design capacity

There are three things that determine how much voltage you'll get from a generator:

1. The strength of the magnet flux
   
   
2. The speed at which the coil legs cut the magnetic flux lines
   
   
3. The number of turns of wire in the coils.

   
   
   

There are two things that will determine how much amperage you'll get:

1. The resistance of the generator windings
   
   
2. The amount of electrical pressure (voltage) you exert against that resistance.

   
   
   

The deciding factor in how much power, in watts, you'll get from a generator is heat.  When you reach the limit of the stator windings you won't get any more out of it and the windings will overheat - the power being generated by your turbine is now being wasted as heat in the generator windings.  The generator doesn't lose any significant efficiency until that point is reached - in fact, if you do some bench testing with any well-designed PM generator, you'll find the drop in efficiency from cut-in to design rated load can be measured in 10th's of a percent.

Realistically, you're talking about a unit that will make, maybe, 85-100 watts in what you say is your average wind speed.  You can get more out of a VAWT if you use a lift/drag wing instead of going with a pure drag design with wind convergence vanes.  But if you check with some of the people who manufacture these, you'll find that even 1 kW units are usually 350lb contraptions - and their rated wind speed is upwards of 30 mph.

VAWT's just have not performed well in the commercial industry and you'll have a hard time finding one from a reputable company that actually works as claimed.  PacWind's Falcon series is one of the only ones I know of that I'd consider as coming from a reputable company that has them installed in various locations, and if you check on the specs of their 1.2 kW Falcon VAWT, you'll see that it's WAAAY beyond what you're talking about building here - and its rated wind speed is 29 mph.  Take a look at its power curve - in the winds you're talking about it barely makes 100 watts - and this is a BIG unit that weighs 350 lbs with no tower.

There's a lot of claims out there by people claiming their VAWT turbines exceed the Betz Limit, or that they operate at higher than 30% efficiency, and that they get this and that out of them.  I've even seen one on YouTube that's supposedly a portable unit, and they show the guy running an air compressor with it for a demonstration - what they don't tell you is that the turbine is NOT running the air compressor.  The compressor is running off batteries and an inverter while the turbine continues to put maybe 50-80 watts back into the batteries.  Most of these claims you can take with a grain of salt.

--

Chris

[fluxable]

Hi Chris,

I think you misunderstand what it is I'm trying to accomplish. I would like to build a generator that has some usable power output at low wind speeds, which are quite common where I live. Also, it is often that we get fairly high winds. So, I would like this generator to take advantage of that, and maximize the output when the wind is blowing strong.

A generator designed with a low cut in speed and low wind speed performance, will reach its limit (just as you describe) much sooner. Thus, the reason I'm suggesting the second stator, to also take advantage of the higher speed. It's cut in speed and low speed performance will be much lower, but will be much more efficient at close to it's limit, which will be higher than the first stator.

I'm aware that the performance of VAWT's are not the greatest, but they are the best choice for use in an urban area. And as long as the wind is blowing, you could potentially be charging batteries for use at a later time. I'm not planning to power my house with such a unit. Just trying to supplement my power needs a little.

[fluxable]

Thanks for the info about the PacWind Falcon series Chris! Actually, I was quite surprised at the outputs they are getting from these units, given there size. Quite promising, but am also surprised at just how heavy they weigh in at too!

The Falcon 3.4 kW unit measures only 3 meters in diameter and 3.6 meters high, but weighs in at nearly 1400 lbs without tower. This also gives rated power output at 29 mph wind speeds. Pretty impressive really for a VAWT! Power for an average wind speed of 4 m/s would yield a power output of under 200 watts. So say 150 watts would yield approximately 1300 kWh per year. Not that impressive, but better than nothing at all. And performance in a semi-urban environment will likely be even less than this.

[ChrisOlson]

The Falcon series VAWT's are lift/drag designs.  This company is pretty straight-forward with their advertising and they don't make any claims that aren't backed up in the real world.  I've personally talked to this outfit on the phone and if I was looking to buy a VAWT this is where I'd go.

I guess I use PacWind's data on their turbines as a baseline when I'm looking at other VAWT designs and the associated performance claims on them.  I went to the Best Buy store in Eden Prairie, MN where they have two of these FAlcon wind turbines installed and running - one is a 1.2 kW and the other is a 3.4 kW.  I talked to the store manager and those turbines work as advertised.

I got a half-completed VAWT project in my shop that I haven't looked at for several weeks because I've been busy with other things.  But it's probably no secret that my VAWT is based on the Falcon design.  My design calls for a direct drive generator with 250 watt capacity, but my VAWT is considerably smaller in diameter (only 4' with 5.5' blades) than what you're looking at, so it will run at higher rpm.

--

Chris

[fluxable]

I'm quite surprised at how heavy the Falcon units are. The generator is likely responsible for a good portion of that weight I'm sure. If that's the case, it might not be a bad idea to install the generator in a small building near ground level, and run the blades up above the roof. If your installing a large unit, you would want to anchor the tower assembly below ground level, as I'm sure the forces on the turbine would be quite substantial! I think I could build a durable unit at a lower weight than what they are specifying. It sounds like these units are built out of steel only?

Good luck with your project Chris, and I'm interested in hearing how it turns out. I will likely start with a small scale project first and see how that goes. Actually, better options for energy supplementing for the home are solar evacuated tubes for hot water heating. I am looking into this as an option too and may even consider doing installations of these to supplement my business here in northern Alberta.

[ChrisOlson]

A generator designed with a low cut in speed and low wind speed performance, will reach its limit (just as you describe) much sooner.

I quoted this one sentence because you're wrong on this.

I don't misunderstand what you're trying to accomplish.  IMHO it's just an unnecessary goal.  If you design your generator for the top end of what your VAWT can make for power, you'll be covered on the lower end.

I don't know if you're aware of the star (wye) and delta configurations of the phase coils in a three-phase generator.  But, basically, you wind your coils with the appropriate turns of wire to get the cut-in speed you want in star configuration with a slow-turning turbine.  And you use the proper size of wire to handle the design amperage at the top end.  When you realize higher rotational speeds you use your voltage sensing circuit and relay to switch the generator to delta.  In delta configuration the three-phase generator will put out more amps and less volts because the resistance of the windings is reduced as opposed to star.

Believe me, you do not need two separate stators to do that.

--

Chris

[fluxable]

I was aware of that option. It seems to me that other manufacturers of wind generators are looking to extend the range of usable wind speed as efficiently as possible. And this makes more sense with the type of unit I'm attempting to build which will be larger in diameter, turn slower, but generate more torque. This higher torque (due to the large turbine diameter) makes a low speed stator more appealing, and then can generate some usable power at even lower wind speeds IMO. While at the same time, I can maximize power output at much higher speeds. I'm talking about using heavier gauge wire and generating high amperage at high speed. The low speed circuit will use many more coils of lighter gauge wire with many more turns per coil, to obtain a decent voltage (at such a low speed) but of course with much less current. I'm basically talking about maximizing the extremes, and with a large diameter rotor, I think I could still get a usable output in a light wind.

[ChrisOlson]

And I didn't have the forethought to post a picture of how you do this.  Here's a photo of a generator I just built with the junction box that goes on the generator:

http://picasaweb.google.com/christopher.w.olson/WindTurbine#5421102993858693842

Notice the junction box for the stator - there's six 30 amp terminal strips in there.  Rather than hard wiring the stator either star or delta in the junction box and running the three legs of the generator to your rectifiers, you run a six wire generator cord from the tower to your turbine control box and make the star/delta connection on the ground, inside your control box.

The three phases have a start and end to each set of phase coils, numbered 1S, 1E, 2S, 2E, 3S and 3E.  For star you hook 1E, 2S and 3E together and the other three are your power legs.

For delta you hook 1S to 3E, 2E to 1E, and 3S to 2S.  The joined pairs are your power legs.  I'll let you work out the details of how you make this switch in the control box with two three-terminal relays, with the star relay NC and the delta relay NO.

--

Chris

[ChrisOlson]

I'm talking about using heavier gauge wire and generating high amperage at high speed. The low speed circuit will use many more coils of lighter gauge wire with many more turns per coil, to obtain a decent voltage (at such a low speed) but of course with much less current.

I quoted this part because this is where I don't think you're seeing the big picture.  Take it from somebody who has a little experience building generators - you use one three phase stator in star and wind the heavier wire with the number of turns required to get your low speed cut-in.  Comparing two stators, one with AWG 14 and 60 turns vs one with AWG 18 and 60 turns, the one with AWG 14 will outperform the one with AWG 18 every time.

Now, when you get to around 23-24 volts you switch the one with AWG 14 to delta and it does everything you're looking for.

I'd suggest doing some math on the situation if that helps - AWG 14 is 395.97 ft/ohm, AWG 18 is 156.62 ft/ohm.  Now, design your two stators, figure out the length per turn and number of coils required to do what you want.  Do another design with just one stator and the heavier wire and switch it star/delta and refigure the resistance in the generator.  I guarantee you beyond the shadow of a doubt the single stator will be more efficient from cut-in to top end than two stators, with one using small wire.

--

Chris

[dbcollen]

The problem with getting power out of low wind, is there is VERY LITTLE POWER in low wind. If there is almost no power there, and you can only harness a small percentage of what is there, the end result is a lot of wasted time and money for no return on investment. If this is just an exercise in mental masturbation, by all means proceed.

Dustin

[fluxable]

I agree that there is very little power in low wind. But if you live in an area where there often is a gentle breeze, and extract that power over a long period of time, it adds up over time. You can use it to charge batteries when a similar turbine may be sitting idle for a large portion of the time. I don't see how that is wasted investment? And to add an extra stator is not that big an investment anyway. It's really like having a turbine that normally (in good winds) runs a direct drive generator at a good speed, but has a smaller reserve generator that cuts in (at a lower wind speed) to generate some usable output, and which runs in a higher gear (effectively). More than mental masturbation in my eyes.

[fluxable]

You are comparing the two gauges of wire with the same number of turns which you happen to state as 60. If you use a lighter gauge of wire, you will be able to put in place much more than 60 turns. By maximizing the number of turns and the number of coils, you will generate more usable voltage, needed at slower rotational speeds. This can also be improved with a larger diameter rotor and stator. It's effectively like running another smaller generator at a faster rotational speed to get usable output. Do you see what I'm saying now? I'm talking about pushing the range of usable output as I mentioned previously.

[scoraigwind]

I can never understand why people feel compelled to use a VAWT in low wind areas.  They are less efficient, so you only end up getting even less power.  Yes there are many 'new' products that Claim to produce with high efficiency.  But if they did then they would be selling really well and we would see them all around.  There's a big difference between claims and reality.

Using 2 stators like that is basically just building 2 alternators.  You can't use the same magnets twice to do the same job.  If you do use the same magnets for both then they will only be half as strong for each half.  Making 2 alternators is basically twice as expensive and completely unnecessary.  Just use one alternator and if you need to change its characteristics, then do this by switching the winding connections around for the different conditions.  The star/delta switch is the easiest way to do this.

Sorry for being negative about your ideas.  I just want to save you wasting time.  Have fun.

[fluxable]

Hugh, I don't see it as wasting time. I think the reason you and a few others that have commented against this idea is in realizing that I am proposing a small or medium size turbine. I agree that it doesn't make sense in a small or even medium sized unit.

 The turbine I'm talking about building will have a large diameter (around 3 meters) and will have the capacity to "essentially" drive a small generator when wind speeds are marginally low. It's not a lot of gain I know, but would be useful to extend the charging of a battery bank. It's a bit of extra expense and effort to give back years of better performance in my mind.