Canyon the big hole in the background is from the two solar driven diffusers. We put the quad and the dual in the deepest water just far enough apart that they could still keep one giant hole open.

Both of my windmills have vertex diffusers. The koenders has a single vertex because it will only make 2 CFM in max wind and I think it's average is much less than that. The frozen over circle this side of the big hole is from the Koenders. The Koenders kept a VERY small hole open for most of the Winter last year.
The American Eagle windmill has a dual vertex on it, but it has already frozen closed. Hopefully it reopens soon. I put the Eagle in a spot I THOUGHT would be better, but it hasn't turned out that way and moving it is a big job. If I didn't have the solar aeration, moving the Eagle would be at the top of the list.

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