Question. Overall, is the heat absorption of the black balls greater than open water? I imagine it's about the same, but perhaps the issue is that the balls are concentrating the heat at the surface, and on the surface of the rotating balls. So it does seem like the evaporation rate could well be higher.
I suppose it comes down to the mean rotation rate of the balls.
Not sure if that's a massive issue, that would probably seal the water off even more effectively. That makes me think that this whole balls idea will limit gas exchange too, i.e. much reduced oxygen absorption, but I guess if they want no life in the reservoir that's not an issue.
Overall though I can't help feeling like there are going to be some significant unintended consequences with this scheme.
https://i.imgur.com/RYyBMrf.jpg
In a reservoir you're not going to get waves that manage to spin the weighted side of the ball up any considerable amount, even if it's only slightly weighted.