Most people don't drive enough miles per day to drain batteries even close to 100%, so that isn't a critical issue. This is why car-mounted PV is being demonstrated, even though for normal-looking cars that PV will only add 10-20 miles range per day on batteries of 100-200 miles — those extra miles are 80-90% of the average vehicle's daily milage.

Also, as batteries can be charged wherever and whenever there is electricity, we can simply install PV enough for the daylight hours to produce the energy desired for both daylight and twilight/nighttime and then just charge daytime and discharge nighttime even though it's probably the other way around wherever you are because currently demand is generally lower relative to supply at night and therefore the electricity is generally cheaper at night.

And the same batteries can easily be given a second life, after degrading too much for car use and before refurbishment/recycling to make them suitable for car use again, as fixed batteries.

And again, this is just presuming only PV, not wind which reduces the variance in supply, and not any of the other things I listed which don't get affected by weather at all.