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Isn't that the idea though? Solar + battery + electric car = no gasoline, electricity, or natural gas bill.

If the average car gasoline bill is $3000/year, electricity is $1000/year, and we demand a 5-year payback, we can spend at most $20,000 on a solar+battery+car system over what we would spend on a conventional gasoline-car and grid-house.

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Yeah, that's the primary use, but there has been speculation here and elsewhere that a battery could be worthwhile just for exploiting the difference between peak and off-peak rates. This indicates that, at least for my area and usage, the answer is no, it's not worth it.

Unless we actually started taxing carbon emissions, in which case you could see those numbers change very quickly. I'm not saying it's likely, but you can't assume your future payments for specific items will stay consistent years in the future.

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