Predicting Turbine/alternator output

[windstuffnow]

  I've been using single formula's to calculate and predict the output of a given turbine with a certain alternator at different wind speeds.  Quite tedious to say the least but I like to know the outcome before I build it... or at least a general ball park idea.

  Yesterday I was determined to come up with an easier solution.  It occured to me I was trying to predict the alternator output after the wind calculations and for obvious reasons it didn't come out quite right.   I decided to approach it from the alternator first then determine the windspeed at which the turbine would match the output and losses.  

   It seems to work out fairly well, I've only run through a couple turbines that I have reasonable numbers on and it matches up quite well.   I made up an Excell spreadsheet from the mess, try it out and tell me what you think!

http://www.otherpower.com/images/scimages/
15/Alternator_windturbine_outuput_prediction.xls

   If you have a specific alternator your going to use and a blade size figured out you can see how they will perform.   It doesn't use TSR, rpm or any linear calculations so if the alternator and blades aren't matched up properly the real life outcome would be considerably different.

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[benjamindees]

That spreadsheet looks like a good start.  That's how I'd do it:  get the alternator modeled well, then work on the blades.  It's nice that it takes into account the varying alternator efficiency (and heat losses) with amperage.

Would you get better results if you let the blade efficiency vary with windspeed?  

Also, I'm curious what kind of physical alternator arrangement this formula assumes?  Is it multi-phase?  What kind of magnets?  Rotor diameter?  Gap?

Since I don't actually have any windmills yet, I'm more interested in the effects of those types of changes on the alternator capacity and efficiency.  

Maybe if we come up with a standardized testing procedure and a list of what kind of data would be needed to create a more detailed, accurate model, people can contribute numbers for the variations that they build.  Having lots of standardized experimental data would help build a good model in no time.

[windstuffnow]

  I've gone over a bunch of different ways of testing... some work out ok but didn't give me exactly what I wanted.  This one seems to get pretty close to the actual outcome.   I think the blade efficiency will remain about the same unless the alternator lugs it down or doesn't load it properly... that's a little more complicated.   If you have a formula for varying blade efficiency I'd like to see it.

  It seems like we've talked about "standardizing" test proceedures but no one has come up with a specific plan.   This is simply one method that I've been using... Still looking for a more compact version.

   The formula's used are bare basic and not formulated for any specific design.  The numbers I used were from the Lenz turbine to see how closely the spreadsheet predicted the output.  I also used my 500 watt kit as a test as well.  The chart comes very close to what the machines actually do in a given windspeed.   I've tried predicting from windspeed and working my way back but it always came in a quite a bit higher than the machine actually produced.  Working it from the alternator up seems to work much better.

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