Then again, the battery pack in the Prius (not Prime) is so small, perhaps it wasn't worth trying to connect the two.
One of the things I do to keep myself accountable for all the subscriptions in modern life is to annualize them, so it's not "just $10/month!" but "$120". But in this case, I think we want to flip it around; at 6 hours of charging you're going to get... approximately two miles per day. Three if you're inclined to round up through the pile of lossy conversions I'm pushing that number through. And that's only going to be in play when the battery is not already full, and it probably won't work while you're charging, either, because the charger will be saturating the battery's incoming charge rate.
I don't find anything particularly unbelievable about that, but it's a marketing stunt, not a good engineering idea, as evidenced by trying to present this in terms of "km per year". That's worthless, swamped in the noise of how your driving style will affect your mileage on an electric car (or any car).
But it's not just about range. Long-term parking of EVs is problematic because if a lead-acid goes kaput after sitting unattended for a year, you're only out $100. But if that's your traction pack, it totals the car. Solar charge makes long-term parking feasible, and enables telematics modems to stay awake, etc.
I didn't say it was nothing, I said it was below the noise floor, which is a much more interesting way of putting it. It's not worth putting a big solar panel on the car and pretending it's going to do anything if the effect of the solar panel is literally swamped by whether or not you had coffee this morning and its effects on whether or not you have a lead foot this morning. Since "literally" has been devalued, let me highlight that I mean it in its original sense; it doesn't take that much of a commute before that will be the case. Or any number of other things that will just swamp this signal, like whether you had to use the electric heater or AC and how much of it you needed, whether you got stuck behind a semi doing 65 for a good portion of your commute or were cruising by yourself at 80 in the left lane, whether the wind was blowing against or with you today, and so on. It's not zero, but it's lost in the noise.
"Solar charge makes long-term parking feasible, and enables telematics modems to stay awake, etc."
https://forums.tesla.com/forum/forums/how-much-battery-charg... suggests drain can vary in the 1-10 mile/day range just sitting there. This wouldn't even cover that entire range, with the optimistic assumptions on how much solar this is producing. YMMV depending on a lot of exact conditions, but it's certainly not the obvious win you'd hope where the solar can overpower normal drain by a clear order of magnitude. (I'm not loving trying to compare two amounts of energy loss in terms of "miles" here, though they're probably roughly comparable.)
It makes me wonder if they've got some other optimistic assumptions in there we weren't thinking of in terms of the car not draining very fast, or even if the number was generated simply by dividing the amount of power it generates by how much power/mile is necessary. Arguing in favor of the latter is that marketers like the bigger numbers, and especially the positive numbers rather than negatives. That post suggests it is likely to be the case that many real customers will at best notice that this solar panel slows down battery drain from just sitting there, but due to cloudy days, winter sun, etc. is not actually capable of overcoming it!
I read those as charging 30-60% of the battery with six hours of charge per day, but I see now that it's six hours a day for 3.5 kilometers per day, and that 30-60% of the battery totally can be charged. Meaning that a car left in the sun for a long period of time can never exceed 30-60% charge.
My bad. Your breakdown makes it more clear that this car is in the same range as my Prius, just marketing the result differently.
This will cut your energy usage by wildly more than anything this solar panel can do.
However, please let me re-iterate, don't do anything stupid. That term will lead you to some stupid things to save trivial amounts of energy.
If you want to save gas go into neutral and go as fast as everyone else or don't do it unless you're alone.
By the way, the best book and/or course I've read for building intuition for these kinds of questions is "Physics for Future Presidents" by Richard Muller. He used to teach it as a course at CMU and I believe the lecture series is still available to watch or listen to online. Very worthwhile.
Even if it doesn't power the motor, a van can have appliances, tools that can be powered by a .9kW setup (I think that could fit on an average van roof)
Also, they have more flat surface for batteries at the bottom too.
I imagine vans use the battery for more than propulsion, so PVs on the roof might be welcome. Charging from a generator is probably still more cost-effective, except for some niches (e.g. boon-docking). Lots of van-dwellers have PVs on their roof.