Why not just dig a hole in the ground and make a gravity battery? Would be much more reusable without all the lithium garbage ... and also probably more efficient...
https://en.wikipedia.org/wiki/Gravity_battery
And the most efficient way would probably be to just have credits with the rest of the city grid. Sell electricity to them when you have a surplus (from solar) and then pay for electricity when you need it. These credits are a lot more efficient than storing the actual electricity in a battery hehe
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