A 5kw system is a big system. Most likely 20 x 250w panels. And with each panel measuring 1 x 1.6m you already have 32sqm of roof covered.
A 5kw system would generate (on sunny days) 25kwh in summer and 15kwh in winter - average 20kwh/day. If you are exporting 2/3 you are using an average 7kwh/day. This is way down the bottom of daily power usage.
An all electric household in Australia uses between 20 and 30kwh/day. To to get away with 7kwh/day means you must have gas or solar hot water, gas cooking and probably gas heating.
PV efficiency also depends in which part of Australia you live in. Alice Springs good, Hobart not so. Don't forget the 250W is peak power in high summer when the sun is at right angles to the panel. More angle = less power and of course more clouds = less power. A street light would contribute bugger all.
So for you to go off the grid - you would be generating an extra 2 days power for each day. If you stored that extra energy on day one and the next 2 days were cloudy as in rainstorms you could survive 2 days. You would need a 15kwh battery. To get through more rainy days, say a week, you would need a 45kwh battery.
Tesla sell a 14kwh battery that they say gets a household through a day and costs $8k + $2k to install. So for under $30k you could go off-grid with your 32sqm of roof coverage.
But you are not average so most people would need to at least double it or triple it (which is where I come up with 100sqm) - and that's only if you have enough roof space facing north. Australian houses with hip and valley roofs don't give much rectangular space facing north.
@WoodySpoon, that was my dream as well a few years ago. But do the sums on a 20kwh/day house plus a 60kwh EV say half charging. The weak point is PV efficiency which is around 15%.
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