You only need a third of that to get the same amount of electricity out of them as by burning 10 kW of fossil fuels. Spread over 20 to 30 years that's suddenly not so much anymore. How much does the US spend on energy each year now? How much to secure the imports?
You forgot that this is primary energy consumption you two are writing about. 10 kW of primary energy consumption if replaced with solar requires only about a third of that to yield the same results since about two thirds are heat losses when converting fossil fuels to useable energy.
If you get 2000 kWh/yr per kWp from PV there and have an installation of 200 GWp you'll end up with 400 TWh per year. If we assume a 25 year lifetime for this installation that's 9600 TWh. At cost of 200 billion dollars, wouldn't a MWh from this system cost close to $21 instead of $1?
Or - taking your numbers - the installation would have to last 400 years without operational costs considered. Isn't that a loss for whoever invests in something like this?
I don't know what Australian electricity needs are, but we averaged 500 W over the last year in our 2-person household. This battery would be good for 10000 similar households for a day or 200000 households "for an hour and 20 minutes...ish".