Their calculations include corrections for capacity factors due to weather. They are probahly a little generous about traffic conditions in some areas though. 40 miles at constant 30mph is very different to stop start hitting 30mph each block or to constant 70mph.

A 100kWh battery is sufficient to average available energy for a 700W panel out over several weeks in summer at lower latitudes, and a month or so in worse conditions.

The idea seems untenable until you consider that it's more like a big ebike than a car. It weighs a fifth as much as a tesla and has under a third of the air resistance.