What is the real power?

[Yianie123.]

Hello everyone.  Your all my last hope when it comes to this question.  I have seen DIY turbines, PMA's and everything in between make claims showing amps, volts, power, but what is reality?  When I see a small wind turbine that can put out 1500W? How is that measured?  After you log the wind speed. Now, you connect to a 12V car battery and measure the amps and then multiply?  In my example, 1500W at 12V (comming off the batter), 1500/12= 107 amps?  I see that everyone advertises there voltage (but isnt  this open circuit?), amps and watts, but isn't everything measured under battery load?  When I saw one honest manufacturer, he does give the open voltage, which was high, amps under 12 or 24v batter load and ended up with a very large Watts number.  But when battery volts was given and the math done again, that very large watts go away, and they are only talking 1/10 of the original number for watts.  Just want to know what I may be buying.  Your help is appreciated.

[birdhouse]

yianinie-
you've about got it.  W= V*A.  so that 107amp number would be correct.  you have witnessed the open volts, shorted amps thing many people try to sell.  it's far from real world, unless you want to spen $800 on a MPPT wind turbine controller.  a controller like this will allow the volts to rise, and convert the higher voltage to what the battery wants to see.  without mppt, the voltage from the PMA is essentially "clamped" at the battery bank voltage. 

basically, if the formula above doesn't pan out, they're lying. 

adam

[Yianie123.]

Not to sound negative, what I am hearing is that these 5ft wind turbines that some are rated 800-1500W is really a scam.  They would have to be in the 35-50mph winds to make even 300 watts of power.  If I am right, then why even purchase a PMA (rebuilt alternator with permanent magnet rotor)?  What can it be used for?

[Flux]

You are absolutely right , this is a complete scam. You are correct, the power is the battery volts x the input current. It is not in any way related to open circuit volts or short circuit current.

The power in the wind rises very rapidly with wind speed and if a 5ft machine is optimised for the high wind then 1000W is not impossible in a gale but it will produce nothing in lower winds.

If optimised for winds of 10mph or less then it won't be efficient or capable of dealing with high winds and will have to furl or be protected in other ways so you would not be able to get much more than your suggested 300W.

I suspect you are referring to one of those car alternators modified with permanent magnets and possibly with a different winding. They do have a use for hydro where a few amps continuously 24 hrs a day can be very useful. They can be used for wind but performance is quite limited and they are little use in low wind areas. With suitable windings they can supply small needs in good wind areas, boats on the coast is one example.

The main purpose for them is to make money for the suppliers from people that fall for the scam.
Flux

[richhagen]

I would also point you to this thread to get some idea of what is likely from a given size machine in the narrow band of wind speeds for which it is optimized. 

http://www.fieldlines.com/index.php/topic,137911.html

[rain1224]

There are some energy unite that you can buy to make some power yourshelf.

[birdhouse]

There are some energy unite that you can buy to make some power yourshelf.

like a genset???