So the original turn key project was 2 Huawei 3KW inverters grid tied with no battery backup. The installer did its job and the system has been working for 3 years now. in Feb 2025, after getting tired of the frequent blackouts and not having my PV system working, I decided to install the victron ESS with 14KWh battery backup. I totally agree about using frequency shifting to AC couple 1 of the inverters on AC Out1 to continue powering critical loads with existing equipment. The problem is I do not have Installer access to my Huawei system to change configurations and the installer does not know how to program the frequency shifting so that opportunity is closed for now, as I must not touch the Huawei installation in order for the warranty to be upheld for the remaining 9 years. Because my ESS is DIY, I have full control over it and hence will be decomissioning 1 of the huawei inverters and the MPPT 150/35 and replacing both with the Smartsolar MPPT RS 450/100. that way I will have 5KW capable off grid system for the outages and 8KW total available when on grid.
Hi Carlos thanks for the info and the outline of your system. I like the DIY side of things just because it gives you options to repair things yourself and replace components at a reasonable price. My inverters are the same in that I don’t have installer access but thanks to the help so far I am happy to leave the PVs and install the Multiplus 2. But I will get a qualified electrician to do the AC side of things and just double check what I have done. I am still deciding whether to go 30kw or 15kw battery as I should stay functional on the 15kw. I feed in more than I use so in theory I should be able to maintain the battery charge. We have regular power outages but only for short periods with the exception of major flood events in which case power can be off for a few days. I am in a sub tropical area so we don’t get long periods of overcast weather.
Qualified electrician inspection is best practice for sure. Regarding the capacity of your battery, it will depend on how much excess energy you are exporting to the grid. Please keep in mind the charging capacity of you Multiplus of choice. One advantage of my system requiring 2 Multiplus for split phase was double the charging capacity for my battery. I found this bit of information on the literature from the victron website to be very useful guide, it shows a ratio of available PV peak power to battery storage:
For my system, I have 8.7 KWp of PV installed. According to my understanding of the literature, I would require 8.7KWp/1.5KWp*4.8KWh = 27.84 KWh total theoretical battery capacity to store all my PV energy and feed very little surplus to the grid. However, because my MPIIs can only charge up to 70 amps at 55.2V, then during peak hours I am unable to capture all available power and still feed a small surplus to the grid. This is why I mention to bear in mind the charging capacity of the MPII you are considering.
thanks Carlos I am still considering 2 x Multiplus 5000.
Based on the the battery calculation I will have to go for the 30kw
Best of luck Kevin. I love my ESS and I love the fact of having full control over it. My local Victron distributor is also a DIY enthusiast so they helped me out a bunch with my learning curve on the installation and programming, as well as setting up the GX control device. The Ekrano GX in my case. The greatest advantage, in my opinion, of going Victron is the modularity. You can start with 15KWh, and then add the rest in the future, dilute the total investment a bit. This is my plan for next year, if all goes well.
Thanks Carlos
Found my research note sources. Hope these help clear any doubts that you may have during installation:
The grid code AS/NZS 4777.2:2020 applies to your Huawei inverters and defines the behavior how to reduce output based on grid frequency.
This called „P(F)“ or Frequency-Watt.
The electrician does not have to program frequency shifting (FS) on the Huawei. FS is to be programmed on the MP2z
Ask you eletrician about the value (or buy the standard online) or look into the RS 450 after setting Aussi grid code.
Than set the same values in the MP2.
After that, you can connect the remaining Huawei (3,5kWp) to AC-out.
The RS 450 charges DC and does not need be considered in 1:1 rule, but for battery max charge current. With 1 MP2 5K (70A) and one RS 450 (100A) you can charge 170 A or ~9,5 kW on 16s (56V) at 25C ambient temperature. Realstic is a little less. 170A is slightly above the limit for a 280-300A cell. Recommended is 0,5C, e.g. 140-150A max. If you have grade B cells, which is normal for home application, I recommend 0,25-0,3 C, e.g. your 30 kWh battery. I have 4x14,4kWh (56 kWh) on 8,5 kWp PV.
If you open the connection to your grid and battery is full, the MP2 will throttle the RS450 via CAN-bus and the Huawei by a frequency of ~53Hz.
If you have significant load, then the frequency will be somewhere between 50,2 and 52Hz throttling the Huawei partly. The RS 450 will adjust faster cue CNN-bus to cope with changing load (PWM) or production (clouds).
Specific frequency are programmed in the ESS assistant on MP2 if AC PV is selected.
At least my system with Hoymiles grid inverters and one SmartMPPT 150/45 behaves like that.
I hope this helps a little.
Thanks for the links Carlos. Mike also recommended Andy’s youtube channel so I will spend a bit more time looking at his videos
Thanks again for your help Bjorn lots to consider.
Hi bjorn is this thread still active as I am not sure how to close it
@Doog
yes, the thread is still open. As thread owner you can mark one reply as solution which will close the thread.
OK thanks Bjorn
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