Well yes it varies a lot by condition, it seems in the worst case (temperate winter, cloudy) you get about 5 miles per day, i.e. about 1 mile per hour of daylig

Well yes it varies a lot by condition, it seems in the worst case (temperate winter, cloudy) you get about 5 miles per day, i.e. about 1 mile per hour of daylight. Still, it does seem like a useful feature. It should be plausible to run out of juice relatively close to an outlet (gas station, hotel, good samaritan, etc.) since electricity is virtually everywhere. Waiting a few hours to get to the nearest facility should not be too bad. It's more of the capability that attracts me (like having insurance without ever needing). Given typical numbers of panel output I wouldn't be surprised if it (nearly) pays for itself anyway, so I don't see the need to be overly skeptical. (ben_w estimates ~1.8 year payback) See other arguments cited elsewhere as well: avoiding deep discharge in case of battery depletion. If you leave your depleted car sitting for a while (days? weeks?), you will see degradation of the precious battery, which represents most (about 40%) of the cost of the car. A cheap insurance to preserve your most vital asset is also a great feature.