First, I work for an electrical company in Europe, and specifically for the department that handles energy optimization and dispatching in an european island of medium size.
I know electrical systems pretty well and the workings of productions that inject in the low/medium voltage grids (namely photovoltaic).
The situation varies for very small installation on the low voltage network (roof 3 to 30 kW) , medium ones in the LV low voltage network (30 to 250 kW) and the big ones in the MV medium or HV high voltage grid (> 300 kW).
All modern inverters may be connected to the internet (or VPN networks) and can be dispatched, that is power can be limited to zero without phisical disconnection from the network. That is not technically a problem for PV.
In small and medium installations the power can not be modulated, that is only left to maximum MPPT or "limited to zero"
In big MV/HV installations you can also tell the installation to reduce its power, for instance to 50% of maximum power.
Utilities is not the correct term, instead we will talk about TSO (transmission system operator) or DSO (distribution system operator).
In big systems DSO (like networks of US, Europe and so on) will mainly make disconnect medium, high voltage PV plants for security reasons, if work on MV HV lines need to be carried out and safety of personnel ensured.
In smaller electrical systems TSO do limit the instant part of photovoltaic (mainly piloting big installations) if they represent too big a part of load. That is because PV/Wind plants are not stable, and do not provide ancillary services to the network, they lack inertia, frequency regulation,etc..
That is why, for now, you need to maintain some rotating machines (hydro, coal, gas, nuclear...) to stabilize the AC electricl system, and thus limit the part of plants interfaced with power electronics (PV, Wind).
Another mechanism that regularly limits PV or Wind Farms productions (in continental europe, and probably other countires) are electricity markets.
In europe, there are reguarly negative prices for some hours a day.
Big powerplants (ex. coal) do not like to shut off for some hours a day (ex PV peak when the offer of energy on the market is too abundant for the load).
These actors on the market will pay through the market other producers (like PV and Wind Farms) to limit their production (they will gain money through negative prices) and let powerplants stay on.
Finally, there are also some other security constraints on big networks where TSO will limit production and will compensate economically (ex wind farms in england or germany)
