With a calculation like that I'd buy solar in a heart beat!

But as I said, my main concern is my winter bill, which I know by asking people who own solar in the region, is almost the same with solar since there's no sun at all (it's not that it's cloudy, it's that the entire day duration is like 4 hours - under which you barely feel any sun heat and in practice the solar output is exactly zero on the worst month and near zero for 4 or so months). Hence the very long ROI here, but I agree that for Queensland, 10 years would be a bit too long if you dimension the solar array properly.