Simple solution for home battery backup and existing solar install?

[gvl]

I have a 9kW array with SolarEdge inverter that was put in service about 10 years ago. Are there off-the-shelf solutions that allow to charge a battery from the inverter (AC coupling I think is the term) in case of a power outage? I realize I will need to install a transfer switch between the inverter and the main panel/grid to be able to charge the battery.

Ideally I envision a poor-man's setup that consists of a backup power inlet feeding the main panel and a mechanical interlock installed on the main breaker. In case of an outage I flip the main breaker OFF/connect the battery to the backup power inlet/turn on the battery and flip the backup power breaker ON, this fools the solar inverter into thinking the grid is connected, it starts to produce power that powers the home and charges the battery. The battery naturally buffers any reductions in solar output.

What are my options?

[organic farmer]

In my system, the battery bank is 48vdc [the amperage is not material to this discussion]. I found a 52 volt power supply online, it may only put out 20 amps but that is enough for a slow charge.

I checked the fluid levels in all batteries, Then started charging. Every day that is was charging I checked the fluid levels again. Eventually after a week the battery bank was fully charged once again.

[gvl]

Just to share my findings, I can do all that with a Schneider XW Pro inverter/charger and 14khw or so worth of batteries. It is being discontinued however, while discounts are good long-term support is a concern. Not convinced I will proceed, but it's tempting.

[solardreamer]

Keep in mind, you will need 2 XW Pro's and 18kWh battery minimum to safely AC couple with your 9kW SolarEdge grid-tied inverter system. Check the Schneider docs for AC coupling.

[gvl]

Yeah, that sounds about right. The 2nd XW Pro is the killer. I rarely see more than 6.5kW output these days from my aging and dirty solar array. What the worst can happen if I use 1 XW Pro? Protection kicks in and it turns off?

[solardreamer]

Most likely protection shutoff is the result. However, the inverter MOSFET transistors may suffer some degradation for each occurrence. So, if this done repeatedly the transistors could suddenly fail at some point. Also, keep in mind that 6.5kW is an average and there could be sudden PV power spikes (I often see this with the cloud edging effect) up to PV system limit (9kW) that can potentially damage the inverter.