Sizing inverter: stacking or bigger?


I’m planing a “simple” solar setup for my new house:

  • 15 * 355Wp LG solar panel ~5325Wp total
  • 20kWh lithium battery storage (2* LG RESU10H probably)
    -> the objective objective is a self-consumption grid-tied system

and I’m blocked by several points:

  • one-phase vs trhee phase inverter ? can i use a 3-phase inverter (better performance, easier to feed the grid) if my grid entry is one-phased ? (most common setup in households)
    Probably not…

  • better to use one 5kW inverter or 2*3kW ? it seems to me that using stacked smaller inverters allow the SP to produce usable power at lower input voltage ? and stacking would allow me to get 6kW output for night time or backup power.

I often see both standard SYMO and SYMO HYBRID inverters on existing setup: what is the interest of having both when the Fronius guide recommend only one depending on the existance of battery storage or not…

Thx a lot for the infos !

Hi OLB, thanks for your post.

As soon as you add batteries, I would say it stops being simple. What is your reason for wanting batteries?

If you have single phase power in your house, you need a single phase inverter.

You should definitely just get a single inverter. There are no advantages in getting multiple, just disadvantages. What you’re saying about voltage, pretty much the reverse is true, and there is also significant extra cost, and double chance of failure.

Symo is for 3 phase, you want Primo.

Hope that helps @OLB.

Let us know if you have follow up questions.


Thx for the answers.

I also thought that 1 phase was the easiest way…

Batteries are the only way to ensure back-up in case of grid shut-down, and/or to provide power during night time.
I’m considering the fact that the extra cost for batteries is far greater than the electricity i might take from the grid… It’ll all depend on the budget I can get.

OK for larger inverter instead of 2 smalls.

The easier the better. I’ll go with SP / inverter / home + grid.

Thanks again to help me clarifying things a bit.


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Batteries are very affordable if you know two things;

  1. Your maximum Daily kWh of Consumption.
  2. What you premises Consumes once your Solar Stops Harvesting energy, through to the Next Sunrise.

As the Minimum kWh battery/energy storage should be 2) consumption.

The better & obviously the more expensive is to have energy storage 1), this will also allow for extended Bad weather, where Solar harvesting may not provide enough energy.

It is very important to divide the Cost of your Battery by the kWh, as this will give you the Cost pet kWh !

As an example LAB (Lead Acid) are the most affordable !

However, the MOST important thing to Remember, is that when you Purchase energy storage, the DOD (Depth of Discharge) dictates the Usable energy from any storage System, and the fact the more you over Drain the energy storage, the Shorter the usable Life Cycle will be !

That statement relates to just about ALL energy storage, other then SC (Super Capacitor Energy Storage modules), that currently claim a 50’000 Cycle life, 50’000 divided 365 =137 Years if only cycled once per day. Worth noting, individual SC Cells can be replaced in SC Modules.
YES, they are dearer, but one of the Great things they offer is VERY quick Charging from 10~30minutes, unlike all other energy storage that takes 4~8hours.

The reduced Module Weight & Energy density/throughput, is said to be why Elon Musk (TESLA) purchased Maxwell, one of the leading SC Manufacturers.

In my opinion, Lithium Batteries will become Cave Man technology in the coming years, especially as SC manufacturing becomes common and other greener technologies are developed…

Good luck with your project.