I wonder how much wattage is coming in from the solar panel? Hard to imagine it being more then 500 watts (with at best 5 peak solar hours in a day that's 2.5kWh). For reference, the Mach-e gets 2.4 miles per kWh. Even with the BMW topping that at 7.14 miles/kWh, I guess an extra 20 or so miles.
I guess it better be all that and a bag of chips with the yuge cost.
Wind resistance goes up with the square of the speed. I suspect it would be a lot more than a 10% reduction in range.