RobA,
I just went to a course put on by a well respected Professor of Aquaculture from Texas A&M. I was considering a windmill also. Here are the facts he gave me. The wind and wave action on the pond adds 10 to 30 percent of the oxygen in the pond. You need oxygen most when the wind isn't blowing. Which also when your windmill isn't working. Electric is the way to go if possible. Hope this helps.
