Solar panels get less efficient as voltage increases, hitting zero at a reasonable point. This is very convenient, since all you need is a buck converter in the battery charger and any unused power can be ignored.

The power still exists, of course. It just ends up heating the panels, which are fine with that.

It looks like FPL has a Net Metering program, which a lot of power companies offer. In short, you get credits on your bill for the power that goes back into the grid. It used to be that some power companies actually write you a check.

https://www.fpl.com/clean-energy/net-metering.html

It's not necessary. If you produce more than you use consistently then a good sized battery bank may be all that you need. A lot of new home appliances are so energy efficient they are starting to see use on sailboats.

Solar cells can produce at load. It's not like panels that aren't connected are melting down, like nuclear.

PV panels are not damaged by no-load conditions.

I assume there's battery systems in place.