That part is independent of internet connection. Especially since you can't rely on the internet connection in case of power delivery issues. It's a completely different network.
If they add up to a percent or two of the local grid, then control is not necessary.
Also you could design a solar system to not backfeed.
The way it works today for common residential grid-ties is this:
1. Is grid up? Y/N
2. If Y, then supply excess locally-generated power to grid. (Someone will implicitly use it.)
3. If N, then turn off connection to grid. (Nobody's home and we don't want to hurt anybody.)
Here in Germany this works by specialised devices called "Funkrundsteuerempfänger" (rough translation: radio controlled receiver, according to Wikipedia[0] it's "radio teleswitch")