Syncing them with electricity is easy. The hard part is preventing export to the grid which requires either a compatible smart meter that can communicate with your panels or a transformer clamp installed by an electrician. My understanding is some meters measure both directions equally so if you do end up exporting power you can conceivably increase your utility bill.
We just got rooftop solar in Canada. Our meter was old and had to be upgraded to bidirectional.
We were warned if we turned on the system before the meter upgrade the old meter would sum together power coming from the grid and power going into it from our solar and we would be billed for the combined.
So with some old meters you don’t want to put power into the grid.
You must live in Europe. Not entirely sure but that's the way things are going in North America, as far as I know all the proposed legislation here is zero export. I guess one concern is local grid instability if too much power is generated this way. Also if for example you put a plug in solar on the same circuit as an appliance that uses its power then the breaker doesn't "see" this usage but it still heats up the wire just the same leading to fire risk, but not sure if this has ever been demonstrated or just theoretical. And also there's the old meters still around that don't measure bidirectionally, so those will just roll back or roll forward each way, neither desirable.
