With $40/kWh batteries available soon, i think even having 100 kWh of storage for a house will be rather common. With 14.4kWp solar, 5 MWh of electricity use per year and 100 kWh at 50€/kWh of battery you have 90% autarky and a time-to-value of 8-9 years. Pretty sweet.
My cheat code for 100 kWH is an EV that supports V2H. It's becoming supported in more cars, so I want to buy an EV as my next car. I don't anticipate battery savings and new tech reaching me faster than replacing my aging car with an EV, hence this path.
I'm in South Africa if relevant, and range anxiety is being alleviated by competition in the vehicle charging space, and municipal grid charging still comes to about 70% cheaper than fuel.
It is also worth noting that you can buy sodium ion batteries if you want to play around with them. The only trick is charging method is not the same as lithium ion, so they need a specialized charger. There are some sources on aliexpress. One listing sells a ~700Wh battery for around $76. So not quite $50/KWh but not awful either.
The discharge curve is also different than lithium ion, so it's easy to see if you actually have a lithium ion battery or a sodium ion.
Not OP, but a recent auction in China has utility scale at $52/kWh. Given the cost decline curve of storage, I would assume we arrive at $40 within 1-2 years.
That $52/kWh is for more than batteries, it's for a fully packaged bulk storage system. So it's quite possible that we're already at $40/kWh for batteries.
Not if you consider that you need to either renew or add battery capacity (and panels and power electronics) after x years? Or did you take that into account?
There is small problem though - all of the people will need the last 10% at the same time. And because you need infrastructure that will work only 10 percent of the time, expect the price of kwh to be 10 times the current to compensate.
The less you need the grid - the more expensive is what you will pull from it because the infrastructure costs will be spread on fewer kwh.
Sadly, it won't matter. Governments/electricity companies have already somewhat adapted:
1) a big part of your energy bill is "connection charge" or similar. Not related to usage but just to be connected at all.
2) they don't allow disconnection
3) most of what you pay in electricity bills is effectively a tax, not for the actual electricity, and isn't really per-kWh. This is masked by the government loading the grid companies up with debt in the past, getting the money and then "making them independent companies", then voting in a levy on tax.
Note I call this masked because the government can't let these companies succeed (it'd be a political disaster if they make real profits, and they can just raise the levy), and they can't let these companies fail (that would mean no more electricity grid for some regions). So it's a matter of time before the government is forced to buy these companies back and all netted out this will just have been a really expensive loan for the government (that past administrations got to spend, and present (it's already begun) and future administrations have to pay)
In some countries there's already talk of giving the grid company the right to charge a connection charge ... when there's no actual grid connection (in Australia), and there isn't even the theoretical option to deliver electricity to an address. Don't worry, they "have plans" to connect everyone (but some of those plans have been there for 80 years and still aren't implemented. But you'll have to pay for just being in the plan)
So the problem is that the government won't let you save money by lowering your usage from normal levels. That would screw up the government budget.
And all they have to do is make connection charge 90%+ of your bill, with some "free" included electricity and your solar installation no longer saves you money.
