Here is a photo I took recently at the seaside near Crosby in the UK.
https://flic.kr/p/Vb6dqtLook carefully at the horizon where the sea meets the sky. The furthest wind turbines seem to be beyond the brow of a hill... except that there is no hill because it's the sea and the sea has to be "flat". Therefore, what you're seeing is the "hill" created by the curvature of the earth!
To my eye, what creates the impression of the turbines being over brow of a hill is the way that the bases of all of them meet the sea at the horizon and no lower.
You need to go to flickr to see the full resolution photo... this forum wouldn't let me attach the full resolution image.