Where to find Alternator for Wind Turbine?

I am building a wind turbine powered by rotating blades although having a different configuration. The diameter of the unit is about
20 feet. Depending upon wind I am expecting 500 Watts to about 4 kW.
Where can I find a suitable alternator / generator?
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wrote:

If you can drive a car alternator at the right speed it will give you about 750 to 1000 watts at 12 volts, more or less. I suppose you want 120 volt AC though.
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Not necessarily. You can get relatively cheaply power conditioning equipment. I've been thinking about a hefty car/truck alternator. I understand there are 24 volt pickup truck alternators. But you have to drive them at a high speed to get much power out.
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