How much power does a wind generator produce?

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How much power does a wind generator produce?

Postby windgat on Mon Jul 21, 2008 10:01 pm

Here is a formula to work out the power produced by a wind turbine.

E.g. at v = 10m/s, 1m radius, 80 percent efficiency

P = 0.354 * 0.8 * 3.14 * 10*10*10 = 889 Watts

(This formula can be used to prove certain marketing claims to be patently false.)
WindTurbineEnergy.jpg
Wind turbine theoretical power
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Re: How much power does a wind generator produce?

Postby Greystoke on Mon May 18, 2009 4:32 pm

Do you have a design for a 1kW turbine :?:
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Re: How much power does a wind generator produce?

Postby windgat on Mon May 18, 2009 9:23 pm

The design on this site is a bit over engineered for the size blades I use. I think it might produce 1kW happily with the right combination of magnets and blade size - perhaps 1.5m blades would do it.
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Re: How much power does a wind generator produce?

Postby Greystoke on Tue May 19, 2009 7:09 am

Could I maybe use multiple sets of stator/rotor combinations :?:
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Re: How much power does a wind generator produce?

Postby windgat on Sat May 23, 2009 12:54 am

Yes you could. I would guestimate this would only be worth it for blades over 2m (i.e. 4m diameter).
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Re: How much power does a wind generator produce?

Postby Greystoke on Sat May 23, 2009 8:53 am

Let me explain what I’m contemplating:

I’ve been thinking of using a wind turbine to power a geyser, by connecting it directly to the heating element.
A wind turbine has a number of advantages over a solar panel, one of which is heating during the night. The geyser also acts as an ideal storage device to smooth the erratic behaviour of the wind. There's also no need to install the geyser in an inaccessible position like above a solar panel. You can place it wherever it's most convenient.

For this to have the desired effect, the wind turbine’s potential power should be at least 1kW.
The geyser heating element is rated 2kW, and this would have to be powered with ±167Veff, or 236Vt by 6A to produce 1kW of heat.

Referring to:
Stator version 3 updated 27 Jul 2006,
8mm thick,
3 phase, 3 coils per phase, 60 winds per coil, 1.0mm diameter wire.
Up to 24V, 10 Amps

To get to 1kW, I would need to quadruple this output.
First, there would be no need for a 3-phase system. single-phase will be enough and there will be no rectification. To safe space I can also reduce the wire size to 0.8 mm.
I’m assuming that each coil @ 60 windings, produces about 24Vt, which means that I need 10 coils in series to get an output of around 236Vt.

What do you think of this plan :?:
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Re: How much power does a wind generator produce?

Postby windgat on Sat May 23, 2009 6:23 pm

I think single phase will cause quite a vibration - it means there are points in the rotation where there is no resistance. Perhaps you can use three phases to three separate heating elements?

The 10Amps is not as far as I know a limit of the generator, but of the mechanisms I have used to turn it (like a 500W motor via a pulley). In fact the other day in a storm I saw 19amps coming into the batteries at one point. Question is at what current the wire would be damaged or melt... for that test I would need a more powerful motor. Also, in a high wind there is a lot of cooling that is hard to duplicate on the test bench.

I think you may get 1kW out of the design just by doubling the blade length (to 2m).

You want to use 0.8mm wire, which makes the melting point that much sooner... there again (I just read yr post again) if you operate at 240V, then 1kW is only 4 amps.

Another thing I would like to try is using N42 magnets (see bench test graph of open circuit voltage on website) at a voltage higher than 24V. 24V is just an arbitrary limit imposed by my battery bank, and at higher RPM more voltage will be generated, eg. at 200RPM over 40V, although that's not high enough for you.

Overall I like yr idea! No more 'cutoff voltage' below which no power is extracted from the wind.

I tried to work out a formula to get volts from Coils, and here are the results, showing volts per 100rpm per winding, and standard deviation:

88 turns, 50x25x12.5 N35 -> 0.302 0.00109
80 turns, 50x20x8 N35 -> 0.173 0.00297
64 turns, 46x30x10 N40 -> 0.401 0.01497
75 turns, 50x25x12.5 N35 -> 0.299 0.00955
75 turns, 50x25x12.5 N42 -> 0.322 0.00152

So for example, for 50x25x12.5mm magnets of grade N35,90rpm gives 0.302 x 88 x 90 = 23.91V (measured value = 24V) (with std deviation of 0.00109).

This should let you get an idea of how many coils would be needed at what RPM.

Bear in mind the measurements were done at different times so may not be 100 consistent, and do not take into account slight variations in air gap size.
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Re: How much power does a wind generator produce?

Postby Greystoke on Mon May 25, 2009 10:52 am

windgat wrote:I think single phase will cause quite a vibration - it means there are points in the rotation where there is no resistance. Perhaps you can use three phases to three separate heating elements?

I did think about that, and I was hoping to mount the coils very close together so that the magnet field would overlap two coils at the change-over point. Hope this doesn't become a serious factor, cause I don't know how to mount two (or three) heaters in a standard geyser.

windgat wrote:In fact the other day in a storm I saw 19amps coming into the batteries at one point. Question is at what current the wire would be damaged or melt... for that test I would need a more powerful motor. Also, in a high wind there is a lot of cooling that is hard to duplicate on the test bench.
I can work-out the resistance of the coils and thereby the anticipated heat loss. I'm trying to keep it to 2 - 2.5 Watt per coil. So far. 0.8mm wire remains a posibility.

windgat wrote:You want to use 0.8mm wire, which makes the melting point that much sooner... there again (I just read yr post again) if you operate at 240V, then 1kW is only 4 amps.
I assumed that 240V would be the peakvoltage. The effective voltage (used as an AC power source) would then be 167V. Therefore, 6A is correct.

windgat wrote:Overall I like yr idea! No more 'cutoff voltage' below which no power is extracted from the wind.
But there is another matter to consider. Something you made me think about doing that "average windspeed" exercise.
Looking at the windspeed forcasts, there are plenty of days where the max speed is 4 - 5m/s. At those speeds I still want a useful power output.
windgat wrote:I think you may get 1kW out of the design just by doubling the blade length (to 2m).
WOW :!:
To heat-up a 100L geyser 30 degrees (ie: from 45° to 75°) over a twelve hour period, you need about 300 Watt. That level should be about a useful minimum. So, the turbine should - on relatively calm days - still produce ± 300Watt.
It follows with:P = r^2 x v^3. and v=5m/s that r= 1.55m. And with v=4m/s, r=2.12. So your suggestion of 2m blades is spot-on.

windgat wrote:So for example, for 50x25x12.5mm magnets of grade N35,90rpm gives 0.302 x 88 x 90 = 23.91V (measured value = 24V) (with std deviation of 0.00109).
Thanks for those figures. It will help a lot.
stupid Q:Earlier you indicated that the figures were per 100rpm. Now I see you are multiplying with 90rpm. :?:
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Re: How much power does a wind generator produce?

Postby windgat on Mon May 25, 2009 12:15 pm

Just checking you paying attention! :D

Actually, I took the /100 as implied. In full:
0.302 x 88 x 90/100 = 23.91 V
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Re: How much power does a wind generator produce?

Postby turning green on Wed May 27, 2009 4:30 am

I bought my turbine !!

Let me just say that I have to go away for nearly two months and so everything stops just here at this point and that's really sad but that's life.

Still I went to Windgat and saw my turbine working !!!! What a surprise for both of us. I had ordered N42 magnets and they were installed. We got quirky results !!!

These magnets are STRONG !!!!! When the voltage reaches cut-in then the rpm is virtually clamped and for a big range of wind speeds thereafter there is very little increase in rpm. A clear case of the blades being too short !!!!

Well Windgat is set up for 1 meter blades with his moulds etc and he said he'd appreciate it if I made 1.5 meter blades to see what happens. Anyway according to the formula at the top in the first posting there should be a doubling of power at 10 m/s from 900 watt to 1.8 kw !!!!!! Now that's POWER. To daydream - 2 meter blades would see a doubling again to 3.6 kw but I think somewhere along the line there will be constraints.

At 1.8 kw one can run a household with the exception of the stove and kettle (gas ??) and the geyser (solar ??). It can take on the fridge (with fairly good winds) which is not trivial. Lighting (within limitations of course) will be a breeze (pun intended).

Incidentally the fridge is my nemesis - I've detailed exactly why in a post under "Wind Power" further down in this General section and it would be so comforting to actually win the battle of Green versus refrigeration.

Well I intend to set up my turbine when I get back - my huge heavy mast is up - and when it's settled down and doing it's thing then I intend to set up my blade making industry. Firstly just making them directly and if they work then producing moulds etc. (my food producing venture will just have to wait).

If it all works out then you will be the first to know (after Windgat that is).
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Re: How much power does a wind generator produce?

Postby Greystoke on Wed May 27, 2009 7:17 am

What do you think of these blades?

Image

Dr. Santoso holds a 500-watt turbine blade
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Re: How much power does a wind generator produce?

Postby turning green on Wed May 27, 2009 8:02 am

The blades look great !! Do you know if he's produced them about 1.5 m long ??
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Re: How much power does a wind generator produce?

Postby windgat on Wed May 27, 2009 8:56 am

I wonder what material those are made from? The smaller blades are often injection moulded, and then I think there is a limit on how long they can be due to strength. Looking closely, the root of those blades looks very thin, I wonder how strong that is?

PS: I love the way the industry commonly calls something '500W blades' for example, without mentioning the wind speed at which that would be achieved! 10m/s? 15m/s? 50m/s? ...
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Re: How much power does a wind generator produce?

Postby Greystoke on Wed May 27, 2009 10:35 am

Dr. Santoso is an assistant professor at the University of Texas, Austin. He specialises in turbine efficiency research.

I think (but not prepared to bet on it :lol: ) that these blades are made of Hi-density Polyethylene, pressed from sheet. They are very efficient.
I have (in the distant past) made blades based on this theory out of plastic pipes (A bit like what Imwithu does). I assure you, they work very well, but you need to use plastic that's strong, or doesn't go brittle, and PVC is just no good.

windgat wrote:PS: I love the way the industry commonly calls something '500W blades' for example, without mentioning the wind speed .....
Was thinking the same thing. Just look at all the adverts on the Internet about what you can all do with a wind turbine . . . Image
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Re: How much power does a wind generator produce?

Postby windgat on Wed May 27, 2009 6:36 pm

What plastic do you recommend that's practical for home builders?

I have used two part polyurethane resin, which is liquid and when mixed sets in about 30 min. Perhaps an idea is to make one blade from PVC, and use it to make a mould for another kind of (pourable) plasitc?
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Re: How much power does a wind generator produce?

Postby Greystoke on Thu May 28, 2009 9:22 am

Here is my first design draft for a 2kW turbine, designed to power a 100L geyser.

Image

PS: I am contemplating circular coils, as I think they may be easier to make. (I'm not that dexterous anymore, so I need to think about that)

This is the general info as I've been able to work out.


Image

Anxious to hear comments.
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Re: How much power does a wind generator produce?

Postby Greystoke on Thu May 28, 2009 10:00 am

windgat wrote:What plastic do you recommend that's practical for home builders?

I have used two part polyurethane resin, which is liquid and when mixed sets in about 30 min. Perhaps an idea is to make one blade from PVC, and use it to make a mould for another kind of (pourable) plasitc?

Hi-density poly in granular form may be a good bet. You could form that by heating the granules and "swishing" the molten syrup around on a preformed blade under a nitrogen blanket, while slowly cooling the plastic down until it sets. (They make kayaks this way).
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Re: How much power does a wind generator produce?

Postby windgat on Thu May 28, 2009 2:06 pm

Some comments:

12 magnets and 24 coils? Is that a single phase?

Circular coils.... its only the up and down vector components of the windings that make current, so wouldn't circles mean less current compared to wedge shaped?

34 turns of 0.8 seems like very small coils - I think you could easily fit more copper in there.

Your tip speed ratio is 3.7? How many blades? That seems small for a 3 blader...
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Re: How much power does a wind generator produce?

Postby Greystoke on Thu May 28, 2009 3:22 pm

windgat wrote:Some comments:

12 magnets and 24 coils? Is that a single phase?
I was thinking of two stators @ 12 positions each, single phase.


windgat wrote:Circular coils.... its only the up and down vector components of the windings that make current, so wouldn't circles mean less current compared to wedge shaped?
Hmmmm . . not sure. The induction is voltage, NOT current, which depends on the area of induction covered by the coil (independent of shape)


windgat wrote:34 turns of 0.8 seems like very small coils - I think you could easily fit more copper in there.
I think you're right.

windgat wrote:Your tip speed ratio is 3.7? How many blades? That seems small for a 3 blader...
Didn't consider this.

There's a number of other things I didn't consider. I think this is a cr*p design :( .
Let me try again.
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Re: How much power does a wind generator produce?

Postby Greystoke on Fri May 29, 2009 7:36 am

windgat wrote:Circular coils.... its only the up and down vector components of the windings that make current, so wouldn't circles mean less current compared to wedge shaped?
The formula =: E=-Nd?/dt, in which E= induced voltage, N= number of windings, ?= magnetic field in Weber.
It's when you work out the force on the wires that only the uprights count.

The only trouble I have with circular magnets is not to let them induce opposing fields into adjacent coils. It's much easier to avoid with rectangular magnets.

windgat wrote:Your tip speed ratio is 3.7? How many blades? That seems small for a 3 blader...
Now I thought I understood you. My mistake. Please explain: What is "tip speed ratio".
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Re: How much power does a wind generator produce?

Postby windgat on Fri May 29, 2009 7:10 pm

Greystoke wrote:Hmmmm . . not sure. The induction is voltage, NOT current, which depends on the area of induction covered by the coil (independent of shape)

:P Whatever! In my setup the max voltage is in effect clamped to 28V, hence I think of current. Point is the same...
Independent of shape?! Can't be... the magnet is moving in a certain direction, and its the cutting of the flux by a wire that counts - so I stand by my comment that circles are less efficient per weight of copper. Only the uprights count! If you are sure that shape is unimportant, try imagining winding the coils in the shape of clover leaves...

Tip speeds... lets open another topic under 'Blades and Hub' for that one.
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Re: How much power does a wind generator produce?

Postby windgat on Fri May 29, 2009 10:26 pm

In a storm the other day I had the 20x50x8mm magnets up with 1m blades. I saw it go to over 19amps, but only caught 17amps with the camera - here's a frame grab from the video:
Amps17.jpg
17 amps
Amps17.jpg (13.82 KB) Viewed 19840 times

With the dump load kicking in at 28V, 19A means 532 watts!
:D
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Re: How much power does a wind generator produce?

Postby Greystoke on Sat May 30, 2009 5:27 am

windgat wrote:... If you are sure that shape is unimportant, try imagining winding the coils in the shape of clover leaves...
I didn't mean that. I meant circles or rectangles. It's the area that counts. The bigger the winding, the greater the fluxchange, the higher the induced voltage.


532 Watts :o That's impressive. :!:
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Re: How much power does a wind generator produce?

Postby windgat on Sat May 30, 2009 7:52 am

Is it not the vector of the wire in the direction of 90 degrees to the movement of the flux? I may be using the wrong words, please correct me if I am...

Maybe a picture will help explain what I mean. Consider the following layout. Which coil will be able to deliver more power(/voltage/current)?
Attachments
coilshapes.png
Is shape important?
coilshapes.png (1.28 KB) Viewed 19830 times
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Re: How much power does a wind generator produce?

Postby Greystoke on Sat May 30, 2009 10:50 am

First coil, but . . .
that's because the second coil doesn't cover the full flux change. It's hasn't enough height compared to the magnet.
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