Agreed. You can increasingly over-provision the solar generation to reduce the proportion of time when you will need a fossil fuel generator or grid input, and install lots of battery to allow the system to smooth over multiple dull days. But chasing that 100% is going to be very expensive, and at some point it'll be much cheaper to have a fossil fuel generator that you need to run 1% of the time.

Yeah, w/o grid fallback, I’d much rather aim for 98-99% w/ solar and have an alternate source to close gap, rather than aim for “five 9s” on solar+batt. It’d take a lot to talk me out of a multi-source approach.