To run my house outside the timeframe that the solar supports I would need at 12.5 kWh battery. Surprisingly there’s not a lot of difference between summer (when we need the aircon deep into the night) and winter (where the electric blanket doesn’t take much power).
The cost varies depending on what you need it to do. If you want to go 100% off the grid, if you already have a solar inverter, if you want to be able to program how you battery charges and discharges, in a black out if you want the battery to take over all of your usage or only part of it. From around $7k to around $11k covers most of the options.
A 12kWh battery would run my TV, NBN, wifi and computers for well over a week without any solar recharging. Solar recharging (even in winter) would mean it would power them forever. It’s stuff like fridges, freezers, stoves, cooktops, water heater, air con etc that really use the power. That’s why decisions need to be made about what circuits the battery supports in a blackout situation.
As an example today my solar system would have fully charged a 12kWh battery before 10am. Whilst at the same time powering all of the house. Even a cloudy day would still fully charge the battery, just pump less back into the grid.
Always a Bulldog