Selectronic Inverter + PV Inverter + Batteries

Does Selectronic have a 1:1 rule like Victron does for AC coupling?

If I have a Selectronic 20Kw Inverter with 2 x 15Kw Symo Fronius PV inverters, how much LiFePO4 battery capacity must I have?

I have read up on Selctronic as much as I can but there is not that much out there (unlike Victron where they are countless posts in forums all about them) and have seen that I can have 2 x the capacity of the Selctronic Inverter in PV Inverters (ie, so for a 20Kw Selectronic I could have 40Kw of PV inverter)…but I can see nothing about how much battery power is required.

Any thoughts on this ?

@Ohms_Cousin Selectronic is only limited to the 1:1 rule when used with a Generic AC coupled solar inverter. If you use a ‘Selectronic certified’ or ‘Scert’ solar inverter such as a Fronius Primo, Symo, or ABB (Fimer) then you have a 2:1 ratio, plus more solar can be DC-coupled if required. Note, the Scert inverters have to be ordered and cost a few hundred more than the standard inverter.

In regards to battery capacity, the minimum battery size will need to be able to meet the demand of the inverters continuous output power rating. However, the SP-link software enables you to de-rate the inverter if the battery capacity is very limited (although this will only really work with a grid connected system)

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Hey Svarky,

Thanks for the info. So how much LiFePO4 would the 120v 7.5KW Selectronic need?

Would that be 7.5KW/Hrs of battery capacity or is battery needed worked out in amp/hrs capacity of the battery pack?

Missed your reply. The minimum battery capacity (or more so the battery output power rating) should be able to meet the continuous inverter power output. For example, the 120V Powerplus LiFe 3.3kWh batteries are rated at 20A or roughly 2.5kW each, so 3 batteries could provide a max of 7.5kW but for a limited time. Ideally, you would want around 6 batteries (19.8kWh), depending on the amount of energy consumption. Also remember the batteries offer 80% usable capacity to maintain the warranty.

Another important factor is the maximum charge rate of the batteries, the Powerplus LiFe 3.3kW have a max 12.5A charge rate (1.6kW) so so a battery bank of 6 batteries can only absorb 9.6kW. The 2 x symo 15kW inverters would be faaaar too big and completely underutilized. I’d suggest you read this article carefully before you do anything further… Technical guide to sizing hybrid inverters and off-grid solar systems — Clean Energy Reviews

Where are you located? This is an extremely complex and powerful system, do you have any experience with AC coupled energy storage systems?