Advice: adding ATS + off-grid inv + battery to ApSystems microinverter setup

[MrNitko]

Hi all and all the best in New Year. Lots of sun

I would like your advice for one challenge for which I have not found an answer where I live.
I am coming from EU, Croatia and have the following setup:

1) House with 3 Phase 220V 50Hz installation
2) 14 solar panels connected to 7 ApSystem's microinverters - 5,76kwp with 5,11AC max output - connected directly to my home junction box with 3 on/off braker switches
3) no batteries - its full on-grid system with export to electricity power grid of the surplus of power not utilized which I can either sell or re-use in the night

I want a most affordable battery system which would allow me to do the following:

1) charge the battery from my house installation when my solar panels are producing the most - does not need to be automatic, auto is a plus
2) go off grid and utilize the power from my batteries when there is a power outage - home backup - does not need to be automatic, auto is a plus
3) go off grid if I want to pull the switch manually - for example storm is coming and as I don't have a surge protection, I don't want to be on-grid

I have researched AC coupled battery packs and inverters, hybrid inverters and have also spoken to some DIY guys who are making batteries. All of them are using hybrid inverters with direct DC solar input or don't have a clue how to help. Therefore I have suggested my own DIY setup which I need your advice will it work properly:

1) installing a 4 pole ATS switch between the grid and my home installation
2) installing an off-grid 3 phase inverter
3) installing a 5kw LiFePo4 battery pack to the inverter
4) connecting the off-grid inverter AC output to ATS generator AC input
5) connecting the off-grid inverter AC input to home 220V socket for battery charging

Would the following work:

1) When I am on-grid (ATS = 1) my microinverts are getting 220V AC and generate power. Inverter is getting 220AC from home outlet and it will charge the batteries
2) When there is no power in the grid or I want to go off-grid
- ATS manually to 0
- First turn off the microinverters braker (they will be off anyhow as there is no power in the grid) not to produce extra power in home network
- Disconnect the inverter input from home 220 AC outlet
- Switch the ATS = 2 - generator mode and use the power from the batteries until they die

Will this work? I don't want to spend a lot of money on inverter/charger and I don't want to trick the microinverters into working while on batteries. I know they have islanding protection so this is not the idea. The idea is just to have power from batteries when off-grid.

What might happen in case I by mistake leave microinverters ON and at the same time use the power from my batteries - how does the islanding protection work - would they just shut down? Or another scenario which I am not aware off: the inverter is still plugged in to the AC home outlet while ATS = 2 and pulling the power from its own batteries? Do off-grid inverters have some protection for these scenarios?

Any advice on the approach or for some off-grid/ats/battery pack models to buy if it will work?

Thank you so much for any advice.

Cheers.

PS. I know that ApSystems offers its own ApStorage and ApBattery solution just for this but its extremely expensive.

 

[DIYrich]

While you are in the process of installing the ATS, install a new Main Service Panel between the grid and the ATS. Move the solar to that, and a 30a outlet.

Plug a Chargeverter into the 30a outlet to grid charge the battery.

When you switch the ATS, you can decide for yourself if you want to disconnect the new Main Service Panel from the grid.

Many off grid inverters have passthorough capabilities, and would simplify what you are trying to do. I don't know EU equipment, especially 3 phase, so don't have any suggestions.

5kWh of battery may be small for a 3-phase system. The kWh of the battery should be atleast the kW of the inverter.