The trouble is that there needs to be some way for the grid operator to take x % of generating capability off-line or bring y % more on-line, and the panels themselves can't decide autonomously, so there must be an external data connection. Maybe not through internet but cellphone data connection, but the grid operator has to have control about how much power goes into the grid.

That's true when there's a sufficient density of home solar panels.

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.

They don't need that kind of control, as evidenced by the fact that this kind of control is largely absent today for residential-scale grid-tied solar installations.

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.)

It’s a bit more sophisticated than that. On a mild sunny day your local network will be saturated with PV power and the supply voltage will creep up. It’s an enforced regulation here (Aus) that the inverters will curtail/shut down based on grid over voltage. No networking required.

I think we're describing aspects of the same thing.

> but the grid operator has to have control about how much power goes into the grid

Here in Germany this works by specialised devices called "Funkrundsteuerempfänger" (rough translation: radio controlled receiver, according to Wikipedia[0] it's "radio teleswitch")

[0] https://en.wikipedia.org/wiki/Radio_teleswitch