Comment by jillesvangurp

It's a nice back of the envelope calculation. I think the conclusions are correct for the stretch goal but it does not make economical sense. Yet (those sodium ion batteries could change that).

There are several things you might want to consider:

- wind, there are smallish turbines that you can put on your roof that generate a few kwh. Also when the sun doesn't shine. Extended periods without any wind at all are rare. 2-3 weeks would be a lot. That probably drops the amount of battery you actually need quite a lot.

- Second hand EVs are relatively cheap and come with some affordable batteries that are probably larger and cheaper per kwh than most commercial domestic storage solutions. Not for everyone but if you can wire things together, that might not be a bad option. Especially if you can get ,a good deal on some well used EV with a half decent battery. Relatively low loads might increase the life that battery has if you just use the car for storage.

- You don't have to generate the power next to the battery. Some cars can provide power to your house; when your house battery runs out, you can just use public chargers and drive back and forth to top up your house batteries. A bit of a chore but probably better than investing in batteries you don't need most of the year. Not a bad option if you live off grid. Batteries on wheels in general are a thing. Electrical semi trucks come with > 500-600kwh typically. That's a lot of power that you can move between your home and your charger. Container sized batteries are a thing. If you want to, you can get about 3-4mwh on your property. It's not going to be cheap. But it's doable. The point here is not that you can have a huge amount but that you could stretch a modest amount quite far by simply driving to and from the charger. Of course if you have a grid connection, using that is more convenient and cheaper.

- The capacity factor of your batteries is going to be a function of how often you cycle them. If you rarely cycle them fully, they are going to be relatively expensive. So, while hoarding batteries might make you feel nice and comfortable, it's not a great economical choice to make until batteries become a lot cheaper.

- The money you save on not paying for grid power needs to be balanced with the cost of a battery and how long it will last you (10-20 years?). If your monthly bill is 100, you might spend 1200$ per year and 12000$ for 10 years. So, that's your budget for a huge battery. If you factor in that it will have a low capacity factor, it might last quite long. Twenty or even more years. I have a lithium ion battery screwdriver that's nearly 20 years old; still fine. Because I rarely use it. So your budget could be 20-30K$ Adjust as needed based on grid prices and usage.

- As others mention, generators are relatively cheap and they do work if you can stand the noise and exhaust fumes. Not clean. But relatively cheap.

It's a valid thought experiment to repeat until the cost adds up. Your opportunity cost while you don't invest in this stuff is basically what you will continue to spend on the grid. Which is probably not horrible for most people. Until those cost curves cross, you are better off waiting. Or compromising and buying a battery that won't solve the whole problem but is cheap enough that it will earn itself back in a reasonable time.

It's trade off between need and cost. If you absolutely need to be off grid, it's doable if you have the space and resources. But it's not going to be cheap. Until then, some hybrid solution is probably more optimal.