Is it safe to say that the ideal (all things considered) a battery that could power the average home for say 24 hrs of "darkness."
On could say 72 hours in certainly locales; hence the modular design.
That said; financially, a goal like 24 hours is unnecessary to realize the majority of the benefits of storage.
So what is it? 6hrs? 10? 12.7? 2? *grin*
Say it's 10 hours; considering metering economics and a theoretical (mental/intellectual) threshold for broad adoption.
The average home in the US uses an average of 32.05 kWh per day. (11,700kWh(yr)/365=32.05)
Lets say the majority of use happens at night; its cold in Philadelphia @ night.
Assume (kinda randomly) 20kWh is consumed AFTER the sun goes down; what if PV array on roof could power the home and "fully" charge the batteries daily.
assuming 153 dollar per kwH that's 3060 for 20kWh for cells. Throw on another 1000 for carriage, inverter, etc.
I think Tesla could easily offer a (nearly closed system) "home storage" solution that meets or exceeds the needs of most for 4k.
What a fun package to offer.
A down payment that gives the home/business owner immediate full ownership of the Tesla Storage system, and they finance, by preferred means, the panels.
(of course you could just roll the cost of the storage in the financing...but I think that immediate sense of ownership of something that is tangibly very valuable; cool, but also relatively accessible financially for not so corporate green types, and young professionals/families; is a neat thing to offer.
Apologies for the ramble.
How many kWhs will the Tesla storage need to be to be most efficient (cost/metering etc); and how many kWhs to be completely self-sufficient? How big do you think the system will end up being?