If it's the ancient practice of crediting on a one for one basis, yeah that doesn't help. (A look around says that's probably where PR is now). If they credit power delivered to the grid based on conditions when it was delivered, then that might help. With appropriate controls, storage can increase grid stability. It would probably be more cost effective to do utility scale storage projects, but project management is difficult in PR; letting those with personal capital hook up solar+batteries and send some of that onto the grid when demand is high seems useful?

These use a form of transfer switch like you’d use when you connect a generator- they disconnect the upstream.

I haven't read the OP link yet, but my guess is they are doing something like this: Grid, Solar and batteries.

You are also sort of conflating "loss of interconnect" with "outage'.

I have no idea about the hurdles of keeping in sync many batteries in many homes connected together. This is not even something I thought about before the news of the blackout in Spain months ago.

It's becoming more and more common for PV systems with a battery system to be able to work in an islanded mode, and more importantly - they're legal and code compliant to do so.

When the grid goes down/out of spec, they disconnect the home from the grid and continue to power locally.

Examples of this include Tesla and Sigenergy.

Some are able to do this in very short periods and able to operate effectively as a whole-house UPS. Some will have a flickr of the lights and maybe some sensitive devices will restart. Others will take some period of time to disconnect from the grid and run in islanded mode.