Interesting, searched about wind turbine once and also got some for income, but not about the combined wind farm, I need to research, I see its kinda recent, 45 tax refund is very nice and income can vary a lot, dunno how it happens. But so, the solar plant also looked like a good deal with + eco energy + dyson sphere, and eco tax is a bonus if so...
But you now are right on whats cost effective, cause their asks went up already, and wind turbine looks better for income now... There is this differential in popularity that will impact cost to fulfill it too, so not such easy math, would need to compare population buildings also, I wasnt even sure on comparision before cause of that...
I'll try to write a post too on whats my overall strategy. Although not a nice guide like that... This one looks very good for beginners.
!PIZZA
Wind Farm lives forever with tax refund while citizens can and will die at some point. I expect prices will change eventually but there is a pretty large supply of Wind Turbines with a decrease in market value.