You need either a lot of panels or a lot of batteries given that there may (or may not) be a constant stream of vehicles wanting to fast charge. Something like a Tesla requires about 50kW to fast charge in an hour so not sure where your 5kW fast charge comes from?
Bottom line, is it isn't really economic to provide the solar array/batteries for a public charging point which has potentially heavy use
The Leaf is 7kw "fast", and about double that super fast.
I have 15 panels, about half of one side of a modest sized bungalows roof. That does 5kW here in the UK. 50kW for a Tesla (not that you see many, with what they cost - they'll never be mainstream) would theoretically the require 10 times my panels, which in a land as vast as the outback is of no concern whatsoever to a country that is willing to tear up land equivalent to the Isle of Wight for strip mining.
But then the sunshine lasts longer and is stronger, so 5 times would probably be more realistic. That would still comfortably fit on the roof of my modest bungalow. That really is very easily achievable, and still far cheaper than a diesel generator that size.
I wouldn't suggest battery to battery for high current applications like this, and thus introducing considerable inefficiencies. Its unnecessary, anyway. Plug the car in, let the sun do the work...unless its night time, but then you wouldn't want an industrial generator running at night either.
Fundamentally though, the average Australian couldn't care less. For them the electric car is an inconvenience, not a step forward, and precious few will understand the irony of using diesel in this way, and most of those that do would probably chuckle at how clever they are.
