Yeah I'll see if I can experiment with that sometime today.
Edit:
Okay I did some experimenting. I wasn't sure if/how to look at my FPS through the game, so all of the FPS recordings are according to AMD Radeon Software. Also, all of the measurements were taken with my settings on "Medium", and were taken in this battle:
Wait nevermind, I'm not sure how to access singleplayer battles.
Also keep in mind that I was never able to fit 100% of the solars/windmills on my screen. Not sure if that greatly effects the FPS.
1,171 Solars:
19 FPS
1,243 Windmills (took up the same amount of space as the above Solars):
19 FPS
1,243 Windmills without wind animation:
20-21 FPS
2,901 Windmills (about 1,496 on screen):
11-12 FPS
2,901 Windmills (about 1,496 on screen) without wind animation:
13 FPS
I don't think my results are super accurate, so someone else should probably also test it.
The without wind animation does seem to help though.