Not to rain on anyone's parade, but hold on to your wallets, fellas:
Those are the same cells that make up laptop batteries. Consider how good these batteries are at holding charge after two years of moderate usage, then consider that there are potentially two consumption peaks a day, so two deep discharges per day. Conservatively, 1000 deep discharges in two years. So count on a "maintenance contract" about 30-40% of capital cost per year, ongoing. And add contingent fees, since demand for lithium is expected to increase significantly in coming years.
(I like Elon Musk's ideas, as a geek, but every time he comes up with a new one, I feel the hand of government reaching deeper into my pockets.)
I'm partial to building dispatchable
generation, myself, but if it's batteries you want, perhaps go for ones that were designed for grid-level storage from the beginning, like the molten salt ones (not MSRs, stuff like Ambri makes), not technologies developed specifically for mobility in more-or-less disposable electronic devices.
BTW, the 1GW for peak is a guesstimate, informed by data from AEMO and a bunch of twitterers (for some strange reason there are lots of people in SA unhappy with the current situation); here's another day in South Australia:
Now, when someone invents a way to use venomous animals to produce electricity, Australia will be ascendant! It's literally crawling with them.
JCS