Vertical Axis Wind Turbine (VAWT)

The blades of the turbine, and the hub they are attached to

Vertical Axis Wind Turbine (VAWT)

Postby Stefan on Fri Aug 15, 2008 11:25 pm

So I am taking the plunge!

I decided on a VAWT design mainly due to the ease of design and build and the fact that I could easily do it with some limited materials I had lying around. Now that I have acually built a test rotor, I am quite surprised at how well it works in light winds (all I have had to test it in so far). So, I am pretty confident about the final product as a small scale turbine. It could however be scaled up a little but lets first see how this one goes. I thought I would just post a little info to let people know what I am doing and try and get some input/advice and comment. So, here goes.

I have gone with a Savonius design I found online. It is based on the following basic design
Image
This is supposed to be more efficient than a regular drag design for 2 reasons. Firstly, the wind coming in the one side is channeled through the center to the other side and expelled, creating some extra force on the opposite end. Secondly, the curved surfaces act like an aerofoil and are supposed to create some lift, which also helps spin the rotor. If these 2 parameters actually make any difference, I don't know, but I liked the design anyways. Here is a pic of my turbine from the top.
Image

I essentially just printed out a template and then cut out 2 pieces of wood in that shape. I then use screws to attache a sheet of aluminium flashing to either side to create the actual rotor surface. The flashing was 50cm x 60cm. The following pic shows a slightly better angle to hopefully give a better idea of what the rotor looks like.
Image

Just in case anyone is wondering, that thing attached to the top is a bicycle front wheel hub, which I plan on using as my bearing. Was the cheapest (R22) and easiest thing I could find that is designed for high loads. Should work ... I hope

I have also created a small (2mb) video clip so you can see it in action. The hub isnt attached to anything yet so I just held it between 2 pieces of wood and opened my front and back door to create a bit of draft. It spins quite freely in only very little wind. The video can be downloaded from: http://users.iafrica.com/e/en/enervate/wind/Movie.wmv <--- (just copy and paste into your browser and you should be able to download it)

I will use the frame that can be seen in the movie to mount the whole turbine in once it is done. It is an old steel fish tank stand so should be pretty stable. Next bit is to find or make a generator. I would really like to make one but magnets are a little pricey and not so easy to come by so I will see what I can find in terms of an old motor.

I can get 50x20x8mm N37 Neodymium magnets but they may not be strong enough as they are so thin. They are kinda cheap at R30 each (R100 for shipping 12). So I might do it and make a generator with 2 rotors, one on either side of the stator, which should maximise the magnetic field. I will see what I can scrounge up this weekend though as I have a few potential opportunities in terms of motors.

I hope you enjoy what I have done and PLEASE COMMENT!!! Let's generate some discussion around this :D
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Sat Aug 16, 2008 10:09 pm

Looks good! More important than how easily it spins is the torque it has, which will come into play when there are magnets and coils.

Do you think the frame disrupts the wind flow, reducing the power? Maybe some sort of solid shaft mounted only at the bottom is better? But the frame will be good for testing either way.

How rigid is the aluminium? There may be some flexing in high wind. If so, metal fatigue will cause cracks eventually.

How do you plan to brace the bottom - a second hub? And how will the rotor plates be attached to the hub?
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Stefan on Sat Aug 16, 2008 11:33 pm

Hey Windgat

Not sure on the torque yet, haven't had a chance to mount it to anything properly yet and put it in some decent wind. I think I may need to make it a bit wider to get more torque out. This is just a prototype to learn off of so we will see. I don't think the frame disrupts too much of the air flow although I was thinking of mounting it with the open side to the prevailing wind. Once I get my design finalised, I will think about a solid shaft mount.

The aluminium isn't all that rigid so would probably crack over time, but again, this is my test rig. Could get it professionally cut and rolled for final version from sheet steel. This would however be heavier. Doesn't seem to be too expensive though.

In terms of the bottom and the hub: I was originally going to use a 2nd hub but was then simply going to attach a threaded shaft directly to the base of the turbine and have the magnet discs on this and then simply have the stator on a bearing and the end of the shaft in a bearing in a piece of wood (or steel) attached to the base. This will change however, depending on what generator I use/make. On this note, let me introduce the gift I received today. I had a very lucky day!!! :D

So I contacted a friend who has been importing various electric bicycles and he had a spare 250W (might be 350W, unsure) DC Hub Motor that he was willing to part with :) LUCKY ME! The motor has a planetary gear system, which I could use to my advantage if I had a turbine with pretty high torque. Here is a pic of the gear system. It wont be very easy to connect though, it seems.
Image

For now however, I will try and connect my turbine directly to the motor. The next picture shows the cog that I would need to connect to. I am not all too sure how I will do this yet :(
Image

The shaft remains stationary and I need to turn that cog. I am thinking of drilling a hole in the wood of the base of my turbine a little smaller than the cog and then filing or cutting out spaces for the teeth and then slipping this over and using this to attache to the base of my turbine. Not sure if this is the best but its the best I can come up with at the moment. If anyone has any ideas, PLEASE POST!! :)

The prototype continues!
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Sun Aug 17, 2008 7:10 pm

Hey Stefan. I think you have the right approach - try it out and see, and aim to make a stronger system once you have the basics working. Looking forward to hearing more!

That is a DC motor? Then it puts out DC directly, via brushes? Some of those motors are AC, and use an electronic controller to pulse the coils as needed. I suggest a first step is to turn the motor by hand and measure the output voltage at various RPM (a bicycle speedometer can easily be used to measure RPM).

I am very interested in those hub motors for another project. Any chance you can put me in touch with your friend?
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Stefan on Sun Aug 17, 2008 10:37 pm

OK. So I eventually managed to attach the turbine to the cog. It seem that it isn't going to produce anything useful. With spinning it by hand, I only got just over 2V but not sure how many amps, my multimeter doesn't seem to be working properly for measuring amps. And that was spinning it pretty quickly. The motor is obviously designed for a much higher RPM and then uses the gears to give the torque at the needed RPM for riding a bicycle. Unfortunately, i cannot think of a way to use the gear system (very very difficult to attach anything to them) and the torque needed is very high. It's hard to turn with your hand. I have the whole thing mounted. Just waiting for some wind to see what comes out of it and how it deals with the load.

So, back to the drawing board.

I am very keen to build an alternator but as you know, I am having troubles getting magnets at the moment and I don't really want to fork out too much more money at this stage. With the 50x25x8mm N37 magnets, do you think I will have a good chance of producing 100-200w? If I build the alternator correctly. I guess we'll need to know what kind of RPM I could expect before we could even begin guestimating. I can get hold of a small 400W controller (takes 3phase AC input) and a small inverter so anything between 100 and 300 watt would be ideal.

What you think?
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Mon Aug 18, 2008 10:37 am

Did you try measuring AC voltage? Just in case...

What is a 400W 'controller'?

And you will need a battery of course.

With only 6 magnets, not sure the power you will get. Hmmm - I have an old rotor pair with 12 x 2 (24) magnets 20x50x8mm which I want to replace with larger magnets. You interesting in taking that off my hands for a mutually negotiated sum?
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Stefan on Mon Aug 18, 2008 1:27 pm

I did not try measuring AC voltage. I will give it a try and see if it picks anything up.

The 400W 'controller' is a 400W hybrid Solar and Wind charge controller. So it has either a 3-phase AC (wind) and a DC (solar) input and then a 12V DC Output for a battery bank. I am assuming that the 400W means it cannot have an input higher than 400W, which is why I am aiming somewhere between 100W and 300W. This 'controller' would be great when I make my own generator as I can feed the 3 Phase AC straight into it without needing rectifiers. And yes, I still need to buy some batteries. Know where I can get some for a decent price?

I was going to use 12 of those magnets. 2 rotors with 6 magnets each. I would be interested in your 24 magnets if you think this will help give my desired output. Can you e-mail me to discuss price? I would also probably need to buy some 'winding wire' off of you to make my coils.

Getting super exciting! I really want to be able to run my light circuit at home off of renewable energy. Shouldn't take too much. I only have 8 CFL lights and rarely use more than 3 at a time. Would be a great start :D
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Greystoke on Sun Jun 28, 2009 7:02 am

Stefan wrote:So I am taking the plunge!

I decided on a VAWT design mainly due to the ease of design and build and the fact that I could easily do it with some limited materials I had lying around.//

In my quest for alternatives, I've also come across some fancy VAWT designs. I think I'm going to study them a bit more closely.

How's this design :?: The center hub floats on a magnet, and the coils that generate the power are at the outer ring, with magnets at the tips of the blades flying over them at high speed. It's about 1.2m high by 0.6m wide . . . . Sexy :!:

Image
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Cor
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Mon Jun 29, 2009 5:39 pm

It would great if you could find some figures and how close to the Betz limit such a design can get.

It looks like a cone, so the area would be about 1/4 of a square metre? That doesn't seem like much power could be generated. I guess you would be very lucky to get 50W in a 10m/s wind.
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Greystoke on Tue Jun 30, 2009 6:42 am

Yeah,
About one turbine for every light in the house :roll:
Although - when mounted on a rooftop - the wind updraft can double the efficiency.

I found this interesting graph:

Image
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Cor
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Re: Vertical Axis Wind Turbine (VAWT)

Postby basiedp on Sun Aug 16, 2009 9:25 am

Good Day all. On Saterday 15/8 I managed to finally assemble my vertical unit for testing. The unit has no geni in yet. At the time off this pic the wind was not strong enough to move the leaves on the tree next to me but the unit was turning with ease. Tried to place 5sec video clip. The geni is ready but want to test the blade desigh before ant major installs.
Attachments
DSC06381.JPG
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Mon Aug 17, 2009 11:11 am

Looks great so far. Crucial issue is of course not how fast it turns without load, but how much torque it can push into the geni.
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Re: Vertical Axis Wind Turbine (VAWT)

Postby basiedp on Mon Aug 17, 2009 4:43 pm

I agree, if the design works maybe will have to enlarge blade size to get over gogging effect or get down to paper and look at another layout off coil to magnet. Currently I have no idea what torque value's are.
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Mon Aug 17, 2009 10:24 pm

No cogging on my generator design! :D

To work out torque, divide power by rotational speed, in radians per second. Or divide by 2 * pi * rpm. Then you can work from your hoped for power, back to your required torque.
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Greystoke on Wed Aug 19, 2009 10:31 am

Output power of a VAWT versus a HAWT

Wind power output = 0.5 x ? x A x v³ x f
In which:
? = air density [kg/ m³]
A = swept area [m²]
v = wind speed [m/s]
f = conversion factor (eg:Betz limit x efficiency)
fmax (horizontal hi-speed turbine) = 0.46
fmax (VAWT: Darrieus )= 0.42
A (horizontal turbine)= ? x R²
In which R = blade length [m]
A (VAWT)= R x W
In which W = width of the swing [m]

Ratio VAWT/HAWT = (W x 0.42)/( ? x R x 0.46) = W/(3.44 x R) = 0.29 x W/R

So,
If you can make a VAWT which is 1.72 times (half of 3.44) wider than the full swing of a HAWT, you should be able to get more power out.

Comments :?:
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Wed Aug 19, 2009 4:20 pm

...wider... than 'full swing'.... :wtf: I am lost.
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Greystoke on Thu Aug 20, 2009 5:26 am

The airflow through a VAWT has an area defined by: square with height = R, width = W.
The airflow through a HAWT has an area defined by: circle with diameter = 2R (="full swing")

:thumbup: :?:
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Greystoke on Thu Aug 20, 2009 8:44 am

For info:(with apologies to basiedp :D )
VAWT02.jpg
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Re: Vertical Axis Wind Turbine (VAWT)

Postby windgat on Thu Aug 20, 2009 5:30 pm

Ok... so Ithink what you are saying is that fmax is 0.42 for Darrieus, and 0.46 for HAWTs.

So a Darrieus needs to be about 10% bigger in area to get the same power?
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Re: Vertical Axis Wind Turbine (VAWT)

Postby Greystoke on Thu Aug 20, 2009 7:18 pm

Ewe! :D
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