We couldn't make the numbers work, we installed a 19kW 3 phase system. Essentially you are spending thousands extra to power your fridges and other standby appliances at night and keep the lights on in case of a blackout. The solar company we used cautioned against a battery due to ROI. If it had enough juice to run my aircons at night in the peak of summer then I would have considered it. As it stands right now with an 8c fit, our average cost is less than $1 a day without a battery.
I'll probably put a 13kw battery in, purely to give some security if the grid starts dropping out.
With battery you get the benefit still generating and using the solar in a power outage. And since we have a young family can use some of the stored energy at night and save peak usage charges.
If we can use a third, store a third and sell a third of what I use in summer that'll be the absolute best scenario.
I've basically come to the conclusion of I write off and forget the cost of the panels as they'll be a longer term asset and replace the battery as needed.
I also looked into a Red Earth Dropbear system. But not really economical
