My source for my previous comment is Bill gates’ book.

Aside, I think a big battery in Australia makes a lot of sense because they have lots of sun year round and lots of unused space. So you are pretty much just storing for night time and can easily build solar panels.

In many other places, you have to store for much longer term which means you need much bigger batteries (and bigger generating plants).

This is to say I think the cost in a place like Australia may be 100s of times less than places in most of the USA (which is where I live).