I'm not sure. The y-axis on this graph is just the rate of power consumption. It doesn't do much for you to use minimal energy while traveling 0 mph.
Efficiency, in terms on miles/gallon, is always a trade-off between traveling fast enough that the overhead of running the vehicle is less significant but slow enough that wind resistance doesn't dominate. There's a sweet spot in there.
Yeah, I'm definitely confused. I don't understand how a car traveling 0 mph can have a finite value on that graph if the y-axis is [energy]/[distance]. I was hoping the units were [Watts][hours]/[minutes] or something to make everything better.
That graph shows a maximum efficiency at around 22 MPH (for the 85 kWh battery), which makes perfect sense -- any faster and air resistance becomes a factor. Any slower and energy uses apart from propulsion begin to eat away at efficiency -- the computer, lights, air conditioning, heat, and so forth.
> Yeah, I'm definitely confused. I don't understand how a car traveling 0 mph can have a finite value on that graph if the y-axis is [energy]/[distance].
The car expends energy just sitting at zero MPH -- the computer and lights, air conditioning and heating, things like that. So the graph is correct -- there is an energy expenditure to "go" zero miles per hour.
> I was hoping the units were [Watts][hours]/[minutes] or something to make everything better.
When the speed is zero, it stops mattering which units it's expressed in. :)
> When speed is zero, distance is zero and energy/distance is infinite.
1. Not energy/distance, but energy/speed.
2. Notwithstanding the cart's labeling ("Wh/mi"), its values aren't predicated on a division of energy by speed. "Wh/mi" doesn't literally mean mean "watt-hours divided by miles per hour", it means "the relationship between watt-hours and vehicle miles per hour".
> Personally, I'd wager they followed the old scientific adage: "If you wish your function to be linear, sample two and only two points".
Yes, except the chart isn't linear. Just for fun, here's a polynomial function that matches the chart's results reasonably well: