This simple:

Trump’s battle against “windmills” began back in 2006 after he had purchased seaside land for a golf course and subsequently learned that a wind farm was being planned offshore. This annoyed him because it would disturb the view and possibly eat into profits. His attempts to prevent the construction of the wind farm turned into a feud with the Scottish government, and in Trump’s mind, converted the wind turbines into giants that needed to be attacked.

“You know, I know windmills very much. I’ve studied it better than anybody.”

That's it. Old man hates windmills. Nothing else to it.