How much power does a wind generator produce?

Anything about construction that doesn't fit into any of the above

Re: How much power does a wind generator produce?

Postby Greystoke on Sat May 30, 2009 11:53 am

BTW: I'v got another design. This time I'm using rectangulat N42 magnets.

Tell me what you think.

Image
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Cor
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Re: How much power does a wind generator produce?

Postby windgat on Sat May 30, 2009 12:14 pm

Aha, I understand, tx. And now I think (finally) my left brain has caught up with my intuition... When the magnet is aligned as on the left, as it 'leaves' one of the coils legs it 'arrives' perfectly at the other. But look on the right - when it 'arrives' at the first leg the shape doesn't match. I think this will mean a weaker voltage pulse when compared to a rectangular or wedge shape?
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Re: How much power does a wind generator produce?

Postby windgat on Sat May 30, 2009 12:45 pm

Ok, interesting.

Is it correct to assume that double wind speed means double the rpm? Are you factoring in the resistance due to induced magnet fields? I don't know enough theory to say if this is a factor or not...

And 0.8mm is okay with 8amps? BTW can you tell me how much current you think is safe to put through the 1mm wire I use?

It would be easier to visualise the whole design with a diagram...
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Re: How much power does a wind generator produce?

Postby Greystoke on Wed Jun 10, 2009 12:39 pm

Greystoke wrote: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. . . .

Not given up on this idea, but . . . - having discussed this with the XYL - I can't justify the expense of R5000 - R6000 on magnets alone. It's just not on, and I'm now investigating the use of a standard mains voltage alternator. The one I'm looking at is about R3000 for 2.4kVA (@ 3000rpm :shock: ).
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Re: How much power does a wind generator produce?

Postby windgat on Wed Jun 10, 2009 3:29 pm

Why so much for magnets? Maybe I can arrange better...
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Re: How much power does a wind generator produce?

Postby Greystoke on Thu Jun 11, 2009 6:10 am

I looked-up the prices of the magents I fancy: discs 25 by 12.5 by 20 thick. Best price: $20 each, and I need 24 of them :!:
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Re: How much power does a wind generator produce?

Postby windgat on Thu Jun 11, 2009 6:36 am

Seems bit like overkill. Maybe more efficient coil shapes plus fitting in more turns would allow much smaller magnets to give the same effect? Remember that even without too much copper packed in and 8cm^3 per magnet (N35) I got over 500W (see above), so with 13.8cm^3 (46x30x10) and higher grade say N40, plus fitting more turns in, it should be possible to get a lot more than that.

And why are you still on discs... :wtf: I thought we agreed discs are not the best shape for maximising voltage?
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Re: How much power does a wind generator produce?

Postby Greystoke on Thu Jun 11, 2009 8:01 am

windgat wrote: . . .And why are you still on discs... :wtf: I thought we agreed discs are not the best shape for maximising voltage?
It's easier to make circular coils. You can also make them very precise. I was thinking of making the coils in two parts, each on either side of the stator disc and exposed to the airflow created by the circulating magnets.
Don't forget that increasing the number of turns on the coil increases the heat losses in the coil, and increasing the wire size lowers the number of turns again. I used a spreadsheet to work out optimum conditions, but It's not perfected yet.

As for discs vs rectangles . . . I'm still undecided. I've worked out the response of a coil moved in front of both magnets to see the difference. The discs produce a (large) leading voltage spike followed by a much lower tail, whereas the rectangles produce smoother, but lower responses that drop to zero the moment the magnet is withing the circumference of the coil.
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Re: How much power does a wind generator produce?

Postby windgat on Fri Jun 12, 2009 10:17 am

So I suppose the issue is which shape produces the higher average 'response'? About dropping to zero... if there are three phases then there is always one phases near its peak.
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Re: How much power does a wind generator produce?

Postby Greystoke on Fri Jun 12, 2009 10:53 am

OK,
I think I've got this thing taped (finally :wink: ) Rectangular magnets give better responses.Image


This is what I've been trying to work out. Two magents: one rectangular and one circular, both with the same strength and area size (1000 mm²)
The coils (also the same area of coverage )are shaped to capture the full magnet flux. The magnets fly past the coils at 1m/second.

Image

These are the responses:

Rectangular magnet:
Image

Circular magnet
Image

I think I finally nailed all the bugs out of my computations, so . . I'm pretty sure about these results. (Although I'm very disappointed in the response levels :? Yet, according to my late professor: A coil that captures 1 Weber in one second, produces one volt.)
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Re: How much power does a wind generator produce?

Postby Greystoke on Sun Jun 14, 2009 7:53 am

This is my design draft for final discussion.

It’s based on the results my computations and windgat’s recommendations.

? I’ve (finally) accepted the rectangular magnets, appreciably increased the number of turns per coil, increased the size of the rotor and stator to speed-up the magnets, and
? gone for a hi-speed 2-blade rotor with a recommended TSR of 6 (not sure yet if I can make such a blade).
? I’ve dropped the wire size to 0.8mm diam, which gives me more space for the coils, but
? I need to ensure good air-cooling to dissipate the extra heat generated inside the coils.

The last point is also the reason why I didn’t adopt the tapered coil shapes as that only increases the resistance of the coil for no apparent advantage. The coils do not respond to magnet movement inside the confines of the coil. Within those confines d?/dt = 0, and therefore the resulting emf = 0.


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Re: How much power does a wind generator produce?

Postby Greystoke on Sun Jun 14, 2009 10:37 am

Problems . . . problems

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Re: How much power does a wind generator produce?

Postby windgat on Sun Jun 14, 2009 10:48 am

What is your altitude (above sea level)?
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Re: How much power does a wind generator produce?

Postby Greystoke on Sun Jun 14, 2009 12:15 pm

I'm about 300m above sealevel.

I'm reposting:

This is my design draft for final discussion.


It’s based on the results my computations and windgat’s recommendations.

  • I’ve (finally) accepted the rectangular magnets,
  • appreciably increased the number of turns per coil,
  • increased the size of the rotor and stator to speed-up the magnets, and . . .
  • gone for a hi-speed 2-blade rotor with a recommended TSR of 6 (not sure yet if I can make such a blade).
  • I’ve dropped the wire diameter to 0.8mm, which gives me more space for the coils, but . . .
  • I need to ensure good air-cooling to dissipate the extra heat generated inside the coils.

The last point is also the reason why I didn’t adopt the tapered coil shapes as that increases the resistance of the coil for no apparent advantage.


Image
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Re: How much power does a wind generator produce?

Postby windgat on Sun Jun 14, 2009 12:23 pm

Ok, you are at sea level.

How do you get a rpm of 458 at 8m/s? I get half of that. Have you perchance confused radius and diameter in you calculation of circumference? :thumbdown:

And do you know the generator efficiency? I.e. mechanical to electrical conversion (or can you estimate?).
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Re: How much power does a wind generator produce?

Postby Greystoke on Sun Jun 14, 2009 12:38 pm

windgat wrote: . . .How do you get a rpm of 458 at 8m/s? I get 225rpm. Have you perchance confused radius and diameter in you calculation of circumference? :thumbdown:
I'll check it out now.

windgat wrote:And do you know the generator efficiency? I.e. mechanical to electrical conversion (or can you estimate?).
Generator output is based on the open coil voltage. It's a bit difficult to work out the loaded voltage. I'm working on that.
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Re: How much power does a wind generator produce?

Postby Greystoke on Sun Jun 14, 2009 12:45 pm

You are right. My mistake. (You're pretty sharp :D )
It's 115 rpm @ 4m/s and 229 rpm @ 8m/s

Hmm, . . .that's going to make quite a difference. At half the rpm, I will only get half the voltage and that's not good enough. (Wonder what else is wrong :( )
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Re: How much power does a wind generator produce?

Postby windgat on Sun Jun 14, 2009 9:08 pm

I think you are aiming at a very high voltage... Other approaches may be to use a transformer, or even thinner wire, or maybe multiple stators/rotors.

In a 10m/s wind, your actual tip speed would be 60m/s. In a gust of 15m/s, that's 90m/s. Would your blade material handle that? Or would the generator load not allow that speed?

I have started to realise that generator load (or resistance torque, or reverse torque... sorry but I don't know the correct terminology) is a crucial part of the design. Its complex, as you say! :problem:
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Re: How much power does a wind generator produce?

Postby Greystoke on Mon Jun 15, 2009 6:18 am

I was thinking about applying brakes @ windspeeds > 10m/s. You see, I don't need 2kW of power to maintain the geyser's temperture. That's for heating the thing up quickly. I'll use ESKOM for that.What I need is a minimum of ±250Watt at average (PE) windspeeds of 3.5-4m/s. At those speeds I need about 85V output to get 250Watt out of the heater element.

I have thought about transformers, but I don't know how they will function at frequencies of 20 Hertz and below. They might just blow up. Also, a 2kVA transformer isn't exactly a cheap thing.

Multiple stators are going to be too expensive in terms of magnets.

I think I'm going to add more windings.
I'll show you the results today.

PS: . . . and the blades are going to give me a headache no doubt Image
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Re: How much power does a wind generator produce?

Postby windgat on Mon Jun 15, 2009 9:52 am

I will help you with the blade profiles... once I know RPM wind speed and desired kW. If you can estimate generator efficiency that would also be helpful. When you are ready :impatient:, post that (under the Blades section) and I will give you chord sizes and twist angles.
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Re: How much power does a wind generator produce?

Postby Greystoke on Mon Jun 15, 2009 1:02 pm

Thanks for the offer. I'll need it.

Got a bit paranoid, so I checked the whole spreadsheet again, and . . . . found another blabs. Resistance calculation was wrong :!:
That and the previous error threw the whole design out the window. (I'm getting old :roll: )
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Re: How much power does a wind generator produce?

Postby windgat on Mon Jun 15, 2009 2:09 pm

Can you imagine how boring it would be if we got everything right first time? :)
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Re: How much power does a wind generator produce?

Postby Greystoke on Mon Jun 15, 2009 3:35 pm

Disagree,
I'd have more time to drink, or perhaps this is God's way of keeping me sober :?:

Anyway, I've tried and turned this design inside out, but no way I can get this to work. I can make the coils bigger, but as soon as they get more than two or three times the size of the magnet, you pick up a lot of peripheral flux that's fogging the main impact, which means that the induced emf is going to be seriously reduced.

So, i've incorporated a pulley system to speed-up the magnets by a factor of four.

Image
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Re: How much power does a wind generator produce?

Postby windgat on Mon Jun 15, 2009 6:10 pm

Ok! I will model some blades for you based on that.

Have you factored in power loss in the pulley?

And did you do an analysis of 3 vs 1 phase? Or even 5 phase?

I take it all yr coils in this design are in series?

Here is a very rushed calculation for your blades. Last two columns are what you are after: blade setting and chord length (linearised for easy construction). Near the root shapes is not important, so just ignore that and make the root in any way you can.

Code: Select all
r      l        f (rads)   f°        b°        C        b         C
                                 (IDEAL)   (IDEAL)   (LINEAR)   (LINEAR)
1980   6.00   0.1107   6.3402   0.3402   152.8800   -0.3348   137.4759
1881   5.70   0.1164   6.6710   0.6710   160.7673   0.3516   153.4893
1782   5.40   0.1228   7.0379   1.0379   169.5027   1.0379   169.5027
1683   5.10   0.1300   7.4474   1.4474   179.2288   1.7243   185.5161
1584   4.80   0.1380   7.9072   1.9072   190.1214   2.4107   201.5295
1485   4.50   0.1471   8.4270   2.4270   202.3998   3.0970   217.5429
1386   4.20   0.1574   9.0193   3.0193   216.3405   3.7834   233.5563
1287   3.90   0.1693   9.7004   3.7004   232.2969   4.4697   249.5697
1188   3.60   0.1831   10.4915   4.4915   250.7262   5.1561   265.5831
1089   3.30   0.1993   11.4212   5.4212   272.2298   5.8424   281.5965
990   3.00   0.2187   12.5288   6.5288   297.6099   6.5288   297.6099
891   2.70   0.2421   13.8697   7.8697   327.9541   7.2152   313.6233
792   2.40   0.2709   15.5241   9.5241   364.7573   7.9015   329.6367
693   2.10   0.3074   17.6126   11.6126   410.0912   8.5879   345.6501
594   1.80   0.3547   20.3231   14.3231   466.8029   9.2742   361.6635
495   1.50   0.4182   23.9625   17.9625   538.5840   9.9606   377.6769
396   1.20   0.5071   29.0546   23.0546   629.1040   10.6470   393.6903
297   0.90   0.6375   36.5289   30.5289   736.5322   11.3333   409.7037
198   0.60   0.8380   48.0128   42.0128   827.4440   12.0197   425.7171
99   0.30   1.1479   65.7723   59.7723   736.9157   12.7060   441.7304
0   0.00   0.0000   0.0000   0.0000   0.0000   0.0000   0.00
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Re: How much power does a wind generator produce?

Postby Greystoke on Tue Jun 16, 2009 8:03 am

Thanks windgat. You'll have to talk me through this slowly sometime. I didn't have much sleep last night. Can't stand it if I have to accept a "cop-out" solution because I can't find another way out. That's a bit of an insult to my intelligence.

Anyway,
(Deep at night) I had another look at magnet prices, and I remembered that there are quite a few small magnets with high fieldstrengths. So I checked them out again and found one 25x25x5 with 981 Gauss @ 10mm distance for $3.14 each. That's not bad.
So maybe I CAN go for a mult-stator design. :thumbup:

Watch this space. :!:
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Cor
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