Good day Everyone

I have a terribly un-unique question.

Currently running a Victron Multiplus II 5kva with some panels and batteries. Currently the limiting factor is panels. I can either:

1) Add Victron MPPT and more panels. OR

2) Add grid-tied inverter to work with the Victron. Victron and SMA or Fronius love working together but I have heard the Solis grid-tie can also work (since SMA and Fronius is so out of my budget).

Would the collective advise to go for option 1 or option 2 or am I missing a 3rd option?

As an aside - I note the Solis S6 4.6 kw has two MPPTs but that they are limited to 14 Amp on input. Interestingly, this rules out basically all the newish higher-powered bi-facial panels.

I am leaning towards option 2 with the caveat of limiting myself to not-the-newest bi-facial panels. The S6 4.6 kw are less expensive that a Victron MPPT and adds inverter power to my setup. Also, installation may be easier in my circumstance.

What does the collective wisdom advise?

Edited August 12Aug 12 by Corné

1 hour ago, Corné said:

As an aside - I note the Solis S6 4.6 kw has two MPPTs but that they are limited to 14 Amp on input. Interestingly, this rules out basically all the newish higher-powered bi-facial panels.

yes, that is a problem, also, note the Victron Factor 1.0 rule
I went for the DC MPPT side, also, since we are totally off grid, I suppose an AC MPPT would also have done here, but certainly we have enough for now (need to actually install a few more panels, but the MPPT capacity is there)

The question of whether to go with AC-Coupling or DC-Coupling should also consider when you will be needing the power.

If you're using the power mostly by day, maybe exporting it, or consuming it instantly as it is generated, then it's probably better to go with a grid-tie inverter on the AC (load) side.

If you're going to be storing power in the batteries to use later, then it's probably better to go with an MPPT on the DC (battery) side.

The difference is in how many DC-AC and AC-DC conversions you will be doing, ie. efficiency plays a role. But it's also taking into account that the inverter's rated capacity is likely to be the bottleneck in your system.

3 hours ago, Corné said:

3rd option

A variation on option 2 is to use microinverters.

AC coupling is always a possible problem, if you can not export, since you are grid connected, you can not tell the AC coupled device (Fronius, SMA, microinverter) to slow down production, since your batteries are full and your consumption is being more than covered, since the frequency is determined by the grid. The DC->AC AC-> DC conversion is, I think fairly low cost, not like a pumped hydro storage, I think its even better than a LiFePO4 battery's round trip efficiency, so AC coupled, great option, possibly, if you are off grid, or, if you can export, else DC coupled solar is probably best.

If my understanding is correct, the Victron Factor 1.0 rule is mostly applicable if I connect the Solis Output to the Victron (which would be ideal since it then continues to supply power even if the grid goes down). I could, however, connect the Solis to the DB directly, "bypassing" the Victron. In this instance the Solis goes down when the grid goes down BUT I do not need to adhere to the Factor 1.0 rule.

Considering the cost and the advantage of having two inverters instead of one, the SOLIS S6 makes the most sense at the moment.

Hi Corne, not really a unique situation. The modern Commercial sites have this type of Micro Grid topology mostly if there are Grid ties involved with a Hybrid BESS system that's are AC coupled on the Load side. The advantage of AC coupling on the load side is the Grid tie gets Voltage ref from the Load side and will produce power all the time. If on the Grid side it will island if Grid power is lost. I used to know the Victron architecture well but I certainly am not current on it at all. The Victron does feature Frequency shifting, however, it's only possible when there is no Grid power involved because it can shift the frequency & the Grid tie will ramp. When there is Grid power that's not an option.

If costs were no issue I'd DC couple with a Victron MPPT because the extra power goes to the Battery and the Mppt will self regulate as it's a Victron product. But price is an issue and the Solis is cheaper. I wouldn't worry about losses at this power level of AC coupling Vs DC coupling I think it's going to be negligible.

There is a another way depending on how handy you can be with HA and Venus OS. Modern Grid tied inverters don't rely solely on frequency shifting to limit power. They also support RS485/ serial Comms & use Modbus. The Solis will definitely feature Power dispatching. Basically you tell Mr. Solis: hey I need 2kW from you & he will produce 2kW. So in HA you will have your instance looking at battery SoC from your Victron & tell the Sols to limit to Load when the battery is above 95%. I actively work in this field with much larger megawatt plants & a controller that can arbitrage and dispatch power as required to service the plant as a micro grid.

However, this is small residential project & all said & done probably the best & bulletproof option is the Mppt from Victron. The Grid tie option is affordable but adding an EMS (Energy management system) doesn't really make financial sense. If you however, you have the time and patience it's doable, there is a Solis integration available on HACS as well as a Venus OS integration. Blend the 2 together and write some automation rules and you in business. Doesn't even have to be complicated, can even program something simple like Above 98% SoC Shutdown the Solis and startup again below 95%. Keep it simple...

On 2026/08/13 at 5:35 PM, Corné said:

Considering the cost and the advantage of having two inverters instead of one, the SOLIS S6 makes the most sense at the moment.

Yes, you can probably set this up as the Grid feeding the Victron, problem is, do you have it connected to the batteries as well? and who charges the batteries, the Solis or the Victron, the Victron would obviously have to go on the UPS side of the Solis and if this is the case, would the Solis be happy to have another generator (the Victron) sitting at its output end? If the Solis is not battery connected, but only grid and UPS to the Victron end, not sure this would actually work, as soon as the grid disappears, I'm guessing so would the Solis, so no more solar power...

So, go on, get a SMA or Fronius and cut the cord, then everything should work out as expected :-) else, ditch the Victron and invest in Solis or do what I did, ditching the grid and getting MPPTs, I could have gotten AC coupled MPPTs, like Fronius or SMA, but didn't consider this an option, after all, if the inverters were to go down, the batteries would still get charged by the MPPTs here... whilst sorting out the inverters... since not telling the inverters about the batteries by way of CANbus messages, the inverters have never gone down, the MPPTs charge based on Voltage, at 55.2V I consider my 16S batteries full 3.450V per cell and that all works as expected. The inverters, of course, can not charge the batteries, since there is no grid, so no need to let them/Cerbo know too much about the batteries anyway, other than, consider the batteries empty at 48V (they aren't but have never reached that level yet).

Edited August 15Aug 15 by Kalahari Meerkat