The microinverters have export control. You can throttle it back to zero if you have the IQ Gateway and App to change the settings. I'm hoping the same is true with Hoymiles. Then it's just a matter of software to replicate what Enphase and Powerwall do for TOU.
As I understand it, Enphase controls power export via the grid CT. That is it sets the maximum voltage of the microinverters such that it applies zero back-pressure to the grid. So, I don't believe it to be a given, but their documentation should say as zero-export is an important feature.
In AC coupling, the two ways I've heard of to throttle a microinverter are anti-islanding and UL-1741. Both are inverter requirements for the U.S., so if Hoymiles is made for the U.S. marketplace it'll have both anti-islanding and UL-1741.
Anti-Islanding allows microinverters to be turned on/off if the grid falls out of spec (voltage and/or frequency) and is the common mechanism that inverters like the Outback GS series uses to control them when AC coupled. The GS lets the battery drain such that there is enough head-room for the charger to absorb any backlash before turning the inverters on (and turns them off when the battery is too full). (Outback has an engineering note on AC Coupling that talks about it).
UL-1741 allows utilities to throttle back DERs via frequency manipulation. Since a microinverter can't tell if it's the utility or an upstream AC coupled inverter it can be used to throttled their output (I'm not sure which (if any) inverter uses that technique to control microinverters).
As I don't see a frequency change when Enphase throttles their microinverters back, I believe they are using their API rather than frequency manipulation as UL-1741 does. Probably because it's too slow for handling surges (for example, at 60 Hz it takes a minimum of 1/60th of a second). Anti-islanding low-voltage is required to take less than .16s. But, both of those techniques require something else to be the brain to control the microinverters, for example to control voltage (e.g., an on/off relay) or frequency (e.g., inverter output frequency).
