At additional cost, one could install a fully manual physical transfer switch which disconnects the PV panels entirely from the gridtie inverter and your apartment's breaker panel, and connects it instead to a charge controller and battery system. Such as one of the nominal 50Ah or 100Ah "48V" Chinese LiFePo4 batteries which come in 2U to 4U rackmount size.

It would be an either/or configuration if done as cheaply as possible such as for a balcony storage system, not capable of both usages simultaneously.

You would then need to have a separate distribution of power from the battery system to your loads. Such as something like a 1000W true sine wave inverter to power essentials like laptop, phone chargers, basic lighting etc during a full power outage.

The small inverters used in these balcony setups aren't setup to provide power without a grid reference.

Yes but they are saying you could - in a power outage - use just the panels, disconnecting them from the grid tie inverter and instead plugging them into a regular off grid charge-controller+battery+inverter setup.

That would cost a bit, but would let you use the same panels for emergency power

The inverter connects directly to the panel and has short DC leads.

Look at the "Component proximity" bit here:

https://robinsun.es/en/products/robinsun-performance-basic-b...

There's probably other setups, but I bet this is how most of the small, cheap ones work.

I’ve not installed these balcony kits, but I’d be surprised if they used microinverters..

Either way, there is no issue using the panels in the kit you linked to in the way described; they are separate panels with standard MC4 connectors. Just unplug the inverter and plug in the grid forming one.

If you look in the menu, I've linked the setup that doesn't include any mounting hardware for the panels, but it's exactly the stuff that's used in the balcony kits.

We've move some distance away from toggling your transfer switch over to the battery charger. Just rewire all the panels, or put in relays at all the DC connections, or...

Huh, for some reason I assumed the balcony kits would be… “dumber”.

Either way, I’ve installed many panels with exactly these little boxes clipped to the back of them, and there is nice clean DC power to pull directly off the panel if you like by just disconnecting the inverter

What I was saying is you completely disconnect the inverter from the panels. The panels become an island, with the positive and negative from the strings instead going through something like a basic DIN mount DC circuit breaker and into the input feed side of a battery charge controller.

I'd be interested to find out what sort of anti-islanding techniques they employ. Most inverters are relatively slow to detect grid failure, and if you pull the plug out quickly you might get a shock.