Hi

I currently have a 3kw Solis Grid tie inverter on the output of my Victron Multiplus-II 48/5000/70 Inverter. I would like to increase the wattage of the grid tie inverter and heard that I shouldn't go over the rating of the Victron itself which is 5000VA. Ratio of 1:1. Would I be able to install a bigger Solis of 6.4KW on the output of the Victron and then use a Solis current clamp and set the inverter not to feed excess power back into the Victron?

Thanks

JB

Hi JB the rule of thumb for ac coupling: Keep Solis grid-tied inverter capacity ≤ Victron inverter rating.

It can work but you need to be sure about the following:

1. Solis zero-export is reliable and fast: The CT clamp must respond quickly to changing loads and stop feeding back into the Victron especially if your batteries are full and there is no path to dump the instantaneous energy.

2. Your loads regularly consume at least 6.4kW, especially during peak Solis generation.

3. You're okay accepting the risk of the Victron overloading if something fails or delays in export-limiting logic.

With Solis, there is no direct control, so you're relying 100% on Solis's CT clamp and Victron is "blind" to what Solis is doing.

Edited July 11, 2025Jul 11 by TaliaB
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Thanks @TaliaB. That makes perfect sense. I think there is too much risk involved and it would be better to keep the grid tie inverter rating ≤ Victron rating.

If you are interested you can ac couple Victron Multiplus-II 48/5000/70 with Fronuis Primo 5.0-1(single phase) with full control. Victron officially supports Fronius inverters for AC coupling using Fronius open API. AC coupling with Fronius is ideal. Let me know should you be interested i could advise on ESS settings or VE. Configuration file between Multiplus-II and Fronuis Primo 5 or Primo 6.

Thank you @TaliaB. I see that the Fronius inverters are on the expensive side but I've heard that they are really good and worth the money. Just to ask another question: If I connect a grid tie inverter to the output of the Multiplus II 48/5000/70 and it is smaller than ≤ 4000W I dont need any current clamp installed anywhere? The Multiplus should be able to handle all excess power even if the load is low and solar production is high? My Multiplus is currently set not to export any excess back to the grid because I cant. (Smart meter)

45 minutes ago, JB0080 said:

Hi

I currently have a 3kw Solis Grid tie inverter on the output of my Victron Multiplus-II 48/5000/70 Inverter. I would like to increase the wattage of the grid tie inverter and heard that I shouldn't go over the rating of the Victron itself which is 5000VA. Ratio of 1:1. Would I be able to install a bigger Solis of 6.4KW on the output of the Victron and then use a Solis current clamp and set the inverter not to feed excess power back into the Victron?

Thanks

JB

May be the ratio is 1 to 1 but a safer bet will be to have the Solis around the 3.2kW max. The Victron do throttle quickly under certain conditions due to heat.

5 minutes ago, JB0080 said:

Thank you @TaliaB. I see that the Fronius inverters are on the expensive side but I've heard that they are really good and worth the money. Just to ask another question: If I connect a grid tie inverter to the output of the Multiplus II 48/5000/70 and it is smaller than ≤ 4000W I dont need any current clamp installed anywhere? The Multiplus should be able to handle all excess power even if the load is low and solar production is high? My Multiplus is currently set not to export any excess back to the grid because I cant. (Smart meter)

Yes it is correct the Multiplis would control and do frequency shifting of either the Solis or Fronuis. There is a lot of info on using the Fronuis but little on the Solis.

I still have to find a post where the Solis grid tied inverters do not work as designed or fails. I have one that is working for 6 yrs without missing a single pulse. They are very robust and tend to switch off if anything is not spot on. Take for instance if it gets a much higher input from panels it will switch off before damaging the MPPT.

As pointed out you don't need the CT for a Solis when the Victron controls the output to grid of the Solis.

2 hours ago, Scorp007 said:

May be the ratio is 1 to 1 but a safer bet will be to have the Solis around the 3.2kW max. The Victron do throttle quickly under certain conditions due to heat.

Yes it is correct the Multiplis would control and do frequency shifting of either the Solis or Fronuis. There is a lot of info on using the Fronuis but little on the Solis.

I still have to find a post where the Solis grid tied inverters do not work as designed or fails. I have one that is working for 6 yrs without missing a single pulse. They are very robust and tend to switch off if anything is not spot on. Take for instance if it gets a much higher input from panels it will switch off before damaging the MPPT.

As pointed out you don't need the CT for a Solis when the Victron controls the output to grid of the Solis.

My Solis must be around 8 years old working reliably every sunny day. I would like to increase my total solar production of my current system and I'm thinking that I should connect my current Solis (3kw) on the output of the Victron multiplus (without a CT clamp) and then add a new grid tie Solis (6.4kw) to Eskom with a CT clamp on Eskom not to export excess back into the grid. I already have a 70A MPPT charger on my batteries so my Victron is maxed out. The only problem with this setup is that I will always need grid (Eskom) power to use the new 6.4 kw grid tie inverter. The Fronius option will work very well but it is on the expensive side.

2 hours ago, JB0080 said:

My Solis must be around 8 years old working reliably every sunny day. I would like to increase my total solar production of my current system and I'm thinking that I should connect my current Solis (3kw) on the output of the Victron multiplus (without a CT clamp) and then add a new grid tie Solis (6.4kw) to Eskom with a CT clamp on Eskom not to export excess back into the grid. I already have a 70A MPPT charger on my batteries so my Victron is maxed out. The only problem with this setup is that I will always need grid (Eskom) power to use the new 6.4 kw grid tie inverter. The Fronius option will work very well but it is on the expensive side.

I have no knowledge of actually doing the connections or how to ensure a grid connection for the 6.4kW to work. If you have a reliable grid like I have then I would not worry about the times when there is no grid and new Solis is idle.

May be our installers can guide you on the path forward.