Would anyone care to explain "cut in speed"?

Discussion in 'General Questions' started by BeachBum, Jul 3, 2010.

  1. BeachBum

    BeachBum WindyNation Engineer

    Thanks for any comments on this topic.
     
  2. windyguru

    windyguru WindyNation Expert

    "Cut in" refers to the wind speed or generator rpm at which a particular wind generator will start charging a battery bank or feeding a grid tie inverter. Two examples:

    1. You a have a PMA generator that produces 13 volts at 100 rpm and you are going to use it to charge a 12 volt battery bank. In order to start charging the battery bank, the generator MUST be generating more voltage than the voltage of the battery bank. Therefore, in this particular case, the generator must make more than 12 volts. So, the "cut in" rpm is 100 rpm. In terms of wind speed, the cut in would be about a 6-7 mph assuming you are using the correct blades.

    2. You have a PMA generator that is feeding a high voltage grid tie inverter. The grid tie inverter input voltage is between 200-600 volts. The cut-in voltage is therefore 200 volts. In this case you would need to use a high voltage PMA that makes around 200 volts in approx. ~7 mph wind.


    Must companies shoot for a cut-in at around ~7 mph wind. Low wind speeds (0-7 mph) have so little energy in that moving air that it is just not worth capturing. To capture it, the stator would have to be wound differently which would make you lose power (amps) at the high wind speed end and that is the power you really want to capture.
     
  3. BeachBum

    BeachBum WindyNation Engineer

    I had read that cut in speed was the lowest speed at which a wind turbine begins producing "usable" power, but didn't understand than any power, even a trickle wasn't worth harvesting. I know that 12 volt batteries charge at 13 volts, but can't the lower 7-12 volt range be used to charge 6 volt batteries? Also, why are 24 & 48 volt battery banks more desirable? I read that 12 volt systems have more "line loss". I guess I still have so much more to learn. Thank you though for taking the time to create this forum, that we all enjoy, and to answer our dumb questions, especially mine. Also, a special thanks to Murray2Paddles, what a great member.
    BeachBum
     
  4. TomT

    TomT WindyNation Engineer

    Without getting too techie. Cut-in speed would be the rpm that the shaft is going fast enough to produce a voltage. Any speed below that and the unit stops producing any voltage at all.
     
  5. BeachBum

    BeachBum WindyNation Engineer

    Thanks Tom
     
  6. windyguru

    windyguru WindyNation Expert

    Well, the higher the voltage of your system the "easier" it is to make more power.

    Power = volts x amps (e.g. the potential multiplied by the current)

    Let's say for your average small PMA, like the WN 500 Watt PMA, you can get 10 amps into your 12 volt battery bank at a particular wind speed. That is about 120 Watts.

    Now take the same PMA and the same wind speed and use those conditions to charge a 24 volt battery bank. If you do this, you will see that the current to your battery will drop but not by 50%. It will drop by about 25%. So you will have about 7.5 amps at 24 volts. This is roughly 180 Watts which is 50% MORE power compared to the 12 volt system.

    Now, you might think why not use a 1000 volt battery bank because I only need to generate 1 amp to make 1000 Watts. Well, there are many reasons why people do not do this but the main reason is for the generator to make a 1000 volts at the "cut in" wind speed (~7 mph), you would need a tremendous amount of thin copper windings in the stator.
     
  7. BeachBum

    BeachBum WindyNation Engineer

    Thank you for the explaination on the battery banks, Windy!
     

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