Keeping in sync isn't as much of a problem as you might think, it simply requires that everything able to feed into the grid has to accept the grid as authoritative for syncing.

Relevant are some of Chris Boden's videos about bringing up a hydro power plant and his comment that you have to be in sync with the grid when you actually connect because the turbine WILL sync to the grid at connection and if it was incorrect before then there will be a lot of loud angry noises from the equipment. https://www.youtube.com/watch?v=xGQxSJmadm0