A 50KW battery is <$10,000. Sounds like he is allowed to sell excess back to the grid and payback period would be <20 years. They are warranted for longer. If

A 50KW battery is <$10,000. Sounds like he is allowed to sell excess back to the grid and payback period would be <20 years. They are warranted for longer. If financing is available it is basically free. ;) Big if that but more realistically the real kicker here is that all of that is about x3 larger than what most households need. I get that not everybody has $10k laying around to plop down on panels/batteries all in one go but if you do you can get off the grid now.