My first PV installation AC/DC coupling

DIY
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1

I’m planning my first PV installation and would like to ask you experts some questions.
I saw there is an option to create an AC/DC coupling solution based on Victron and Fronius.
This is new to me and I’m still learning about this, so please forgive me if some of my questions seem basic or lack clarity.

Questions:

a) Integration of Fronius and MPPT on the DC side:
What is the proper way to integrate the DC side to use Fronius and MPPT from one string?

  • Can someone share detailed wiring diagrams? I found one example, but it doesn’t clarify if the DC is connected via a busbar or another method. Is this good location for BusBar?
    or I will need to use separate strings for each?
    Screenshot 2025-01-11 at 11.56.53
    Screenshot 2025-01-11 at 11.56.531920×748 65.1 KB

b) Load balancing for Multiplus II in a three-phase setup:
If I use 3 Multiplus II 5000 units and need more power on L1, what are my options?

  • Should I replace the Multiplus on L1 with an 8000 model while keeping the other two as 5000?
  • Or do I need to replace all three units to maintain balance in the system?

c) AC input connection with mixed devices:
In another scenario, is it possible to connect the AC input as follows?

  • L1 → Quattro II
  • L2 → Multiplus II
  • L3 → Multiplus II
    The purpose of this design is to allow dual inputs on L1. Will this configuration work without issues?

d) Zero Export
what would be best configuration for AC/DC coupling with Fronius and zero export. I will appreciate is anyone can share some diagrams.

e) Final Question: Optimization
If I use Victron and Fronius in an AC/DC coupling configuration with zero export, how can I manage PV shading?

  • Do I need to install additional devices on each PV panel to optimize performance?
2

Hi answers on your questions:

A)
you cant! Its either fronius or mppt, if you want both you need to split solar panels up

B and C)
All units need to be the same type hw and fw version

D)
Fronius can be on ac in or out, mppt is dc side
GX device can be set to zero export, so it throttles fronius and mppt when needed, you will need a supported grid meter for this

E)
You can use multiple mppts
look at the amount of panels you want to install and in what orientation, and divide them up over sevral mppts or (fronius) inverters

3

Thank you for the explanation; it helps a lot.

The main goal of my questions was to find the best solution for the following:

  1. Zero Export to the Grid: Ensure no power is exported to the grid, while still using the grid as a backup source when there isn’t enough power from the PV system or generator.
  2. AC Coupling for Future Expansion: Use additional inverters on the AC side to expand power production if the load increases in the future. From what I understand, Victron and Fronius can communicate with each other, but is there a comprehensive list of other devices that can interact with Victron in a similar way?
  3. DC Side Configuration: Configure the DC side so that power from a single array is shared between the additional inverter and the MPPT. For example, during high loads, all the demand should be met by the array via the Fronius inverter first, and rest should go to MPPT. When the load decreases, more power should flow through the MPPT to charge the battery, minimizing energy loss from triple conversion.

I’m unsure if this type of priority-based distribution is feasible, which is the source of my confusion.

4

Zero export to grid is possible but depends on settings, in ESS mode you cant get zero but close to it, ESS will always balance on grid

  1. Fronius can communicate with victron other brands not, however all pv inverters are compatible on ac out if they support frequency shifting

  2. As i already answered to your first post
    You cant share power from a single array, its either on an ac pv inverter or on an mppt, you can have multiple arrays each wired to its own mppt or ac inverter

Power from ac pv inverter or mppt can always be used for powering loads or charging batterys

I also advice you to get information dor your specific setup from a official local victron dealer, and there are a lot of manuals to read, you can also follow free online courses at the victron professional site