Understanding Victron MPPT VOC limitations for a potential inverter switch

Q&A and troubleshooting
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Hi All,

I’m looking into potentially changing my current inverter (=SMA Sunny Boy 3.6kW) to a Victron inveter/ DC low-voltage home battery combination.
But i’m having some issues using the Victron MPPT calculator, and wondering if someone can explain a few things.

I have an regular 40 to 45 degree roof with 2 strings of 12 Eurener 280Wp panels in an East - West orientation
From what I can see in the datasheet, these panels have a Voc of 39,10V. Resulting in around 470V or 538V if you take 15% margin into account

I I try to enter this value in the Victron MPPT calculator, the maximum amount of allowed panels for 2 strings seems to be ±9.
Question 1: Is my understanding correct that this is due to the current Sunny Boy Inverter allowing up to 600V, where as Victron only goes to around 450V?
Or am I misinterpreting something here? And does this apply to the MPPT’s individually, or combined?

Question 2: the current wiring between the attic (which holds the PV setup) and the ground floor does not have a separate cable that can be used for a power sensor. But the attic does have a rock-solid Omada (Ethernet/Wireless AP) setup.
Would a Victron system with a VM-3P75CT that supports Ethernet be able to communicate efficiently with a Cerbo unit in the attic connected via Wifi, so the system knows when to charge/discharge.

Important to mention:

  • The 230V wiring between the attic (which holds the inverter) and the ground level with the main electric setup is only 3G2,5mm2.
    Which limits my AC output to 3600W to 4000W. One of the downside of renovating at a relatively young age 15 years ago - you’re not smart enough yet to plan ahead.

  • I’ve included a screenshot of the actual AC output of the current inverter, during a near perfect summer day.
    This should explain that apart from 2 tot 2,5 hours day the total system output rarely gets close to the peak value of 3.6kW

    image
    image3449×983 80.8 KB

  • If the above is not feasible, I could also consider an AC coupled setup on the ground floor. But the current inverter is 7 years+, and i’m not that keen on losing space on the ground floor + coping with the additional conversion losses.

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Yes.
More of that, not 450V, no more than 8 times the float voltage, so, if 54V float, no more than 432V.

2.5mm2 will hold about 25A, if the ambient is not above 30 deg.C and the cable will not exceed 70 deg.C.
I am using the same setup as you, with 2.5mm2, and when drawing 4kW, the cable is just slightly warm. So no worry.

The rest is feasible.
You are looking at something like this below, just that the comms between router and Cerbo will be wifi, right?
Picture taken from the Multi RS manual.

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By the way…
An off-topic question…
Why change SMA with Victron? Some shortcomings with SMA? Power output?
I have an acquaintance who, in the same situation, has choose SMA instead of Victron…
Thanks.

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Thanks for the reply, that means I can’t change my current 2x12 setup to a Victron based solution since I have too many panels per string.
Or would need to change that.

I’m actually quite happy with the SMA Sunny Boy 3.6, but it’s already 7 years old and not a hybrid inverter.
Switching to a hybrid Sunny Boy Smart Energy + HV battery would set me back around 7k€, going to another hybrid inverter + low voltage battery can be done at a fraction of that cost. Like sub 2k € for ±15 kWh battery capacity. But then I run into the issue with the current wiring not supporting a power meter cable…

Due to some recent changes in the regulation/legislation over here in Belgium we now have digital power meters - which makes storing your own solar power much more interesting. At the same point in time, i’d like it to make sense in economical way

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