battery inverter: modulate output power?

[SebKuzminsky]

Hi there, i'm new to the home power game. I just got a 10 kW grid-tied PV array installed, all Enphase gear with micro inverters. I've had fun charging my EV using surplus power from the PV system: https://github.com/SebKuzminsky/solar-evse/

I have a couple of kWh of second-hand batteries (48V nominal) with a matching charger, and i'm thinking of building a system to do this:

1. When the PV array is producing: use surplus energy to charge the batteries up to 80% SoC or so. When the batteries are "full", export any surplus energy to the grid. I'll modulate the charger current like i modulate the EVSE in the project above to avoid importing power from the grid to charge the batteries. The charger is a DeltaQ ICL 1500, the charge current is controlled over CAN.
2. When the PV array is not producing: turn on an inverter to supply the house from the batteries. Draw the batteries down to 20% SoC or so, then turn the inverter off and import whatever power the house needs from the grid.

I feel pretty confident about 1 above, but i have some questions about 2.

All the inverters i'm familiar with are pretty dumb:

• You turn them on and they just supply whatever the load asks for, until they overload and shut down, or until the battery drains and they shut down.
• They don't want to be connected to an existing AC grid.

I want a smarter inverter that acts more like the micro-inverters on my PV panels, specifically i want to be able to tell the inverter how much power to pump into the existing house wiring. Ideally open source hardware but that might be asking for too much....

In the closed-source/proprietary space, the Enphase IQ8X-BAT looks like it does approximately what i want, though i'm not sure if it's controllable from the outside like i want.

Does the thing i want make sense, or am i thinking about this problem wrong?

Does such a thing exist?

Thanks all!