AC-coupled setup questions

DIY
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1

Hi,

I currently have a DC-coupled system with around 12kWp solar (pointing different directions, max I ever get is 10kW), 15000 Quattro and 15.4 kWh 48V battery.

The setup is single phase, grid input capacity is 9kW but I internally limit grid feed in to 8kW

I am looking to get AC-coupled setup (Fronius) and I am not sure about the following:

  • If grid is ON, how does the PV output regulation work? Would the DC-coupled system decrease its own output in case the sum of both AC and DC would exceed the grid feed-in capacity and let the AC-coupled run at the max? The AC-coupled system in my case will not exceed the 8kW grid feed-in capacity so no need to worrry about it being throttled.
  • AC2 of my quattro turns off when grid fails. Am I correct in thinking that I ONLY need to follow the Factor 1 rule on my AC1 and can connect anything beyond that to my AC2 (another inverter), knowing that if grid fails that is turned off immediately as well?

I am considering adding around 3.8kW to the AC1 (which should be below the Factor 1.0) another similar sized one to AC2 later.

2

With a fronius there is feed in control.

You can set up how much excess to feed. This throttling is done through mod bus to the Fronius when grid connected.

Everything you need to know is in the ESS manuals

Your input current limit on your system will also limit the feed.

The 1:1 rule refers to inverter sizing. Not loads sizing. If it is a 15kva Victron inverter the max ac coupled pv is 15kva

3

Thank you!

I thought I was also limited by the battery? I’ve calculated the 3.8kW by the inverter size.

My understanding was that the Fronius would “talk” to the Victron system via listening to the frequency shifts. Hence my questions as there is no frequency shift when grid-connected, if I understand it correctly.

If I configure the Fronius-Victron comms to be via Modbus (over TCP, right?), is frequency shifting redundant?

4

Well if you battery is sized for the full inverter load in amps then it won’t be a problem. Obviously if it cant do the charge and discharge of the inverter, it will be

Yes it is in the fronius Victron manual how to make sure comms work. it is modbus controlled.