From the article "Even with these rough numbers it’s hard to see how anyone living any distance from the Equator is going to be able to justify the cost of installing enough batteries to go off-grid with a domestic rooftop solar PV installation."
If you go off grid on purely solar your backup is not a battery, your backup is a genset.
It's a nonsense proposition leading to nonsense conclusions based on nonsense numbers. Very tiring.
With that said, from reading some articles about off-grid living, it's not outwith the bounds of possibility that people are looking at pure solar (or pure renewable anyway) off-grid living, for priniple-based reasons , rather than a more pragmatic rationale.
Back in the real world you wouldn't design your system that way. Instead, you would look at your worst case scenario - mid-winter, and calculate how many solar panels you would need to capture a day's worth of energy in one day. This would also tell you how large your battery would need to be. A prudent engineer would probably introduce a factor of 2 or so both in the size of the panel installation and the size of the battery to allow for a sequence of unusually dark days, but the multiples being talked about in the article are just ridiculous.