Grid in-line topology with PV inverter question (power assist?)

Q&A and troubleshooting
, , ,
1

Hi

I’m in Australia and am preparing to add batteries to an existing battery-less Fronius system.

I have a question regarding the use of the Multiplus 2 in the grid in-line topology. The documentation doesn’t specifically list the maximum load on the “no-break” or “critical load”.

image
image960×1007 98.4 KB

Say I have a 5000VA Multiplus 2, and the sun goes down, but the grid is available, and the load is 8000VA. Will the Multiplus 2 supplement 5000VA from the battery with 3000VA from the grid?

I understand that when the grid is out (rare), that if the load exceeds 5000VA, the system will shutdown. I am fine with that. But basically, I am looking to simplify the household wiring, not divide circuits into critical and non-critical. In a grid blackout, I am happy to monitor my usage to ensure I don’t exceeed 5000VA.

I feel like Option 2 in this image, with all loads on the orange side, is what would be easiest to build. I understand I would need to obey the 1.0 rule.

image
image981×1648 81.2 KB

2

if the load exceeds the continuous maximum for the inverter, then the inverter will switch to grid, and if the grid current gets close to the maximum set, the it will use power assist mode to source the extra power from the battery.

so the scenario of an 8kW load drawing 5kW from the battery and 3kW from the grid is incorrect, more likely to be 5kW from the grid and 3kW from the battery, depending on exact settings.

Also the 5000 inverter does not support 5000W continuous load. Do read the specs carefully before deciding on the equipment.

3

Hi Mike

Thanks for your reply. I have taken a look at the specs more closely, and I will frame my question with more accurate numbers. My basic question is “will the Multiplus 2 use both grid and battery if the load is higher than the Multiplus 2 nameplate, and will it use the battery first”.

Also, this is all in the ESS mode. https://www.victronenergy.com/upload/documents/Energy_Storage_System/6292-ESS_design_and_installation_manual-pdf-en.pdf not in the offgrid mode.

These are the critical specs for the MP2:

Max continuous output power at 25C: 4000W
Max battery discharge current: 110A

This suggests the MP2 would be able to generate 4kW at 25C continuous with a full battery.

Using the “Option 2” topology, the PV inverter producing zero, and the grid active:

  • With a 3kW load on the orange output, the MP2 should supply all power from the battery
  • With a 6kW load on the orange output, will the MP2
    1. shut down?
    2. supply 4kW from the battery and use 2kW from the grid?
    3. switch the load to the grid and use 6kW from the grid?
    4. something else?