The only way I see it possible to exceed 400 MPGe at this point requires absolutely ideal conditions, very slow speeds, and relying upon the solar panels for full production (which I doubt will ever happen).
Using the specs from their site, the panels provide a maximum of 1.27kW.
So lets just assume that this car can regularly actually sustain 200 MPGe, or 6-ish mi/kWh at 35 MPH. In one hour, the car would obviously travel 35 miles, consuming about 6kWh. Subtract full production of the panels to see about 4.7kWh pack expenditure. Flipping that back to mi/kWh, we get about 7.4. That is still well under 300 MPGe, or most roughly, just under 250 MPGe.
The only ways to get over 400 MPGe with those calcs in mind are to assume one or more things to be true:
1) This car sees significantly over 300 MPGe in typical driving,
2) They are lumping in potential power production from the panels while parked, or
3) It must be driven far slower.
But if we get to add in solar panel production, I am going to take credit for the 5 kW array on my home, the less than 100 miles I typically drive in a week, and always charging at home (when I'm not conducting flawed aerodynamic tests
). The numbers on that cross infinity in all but November and December here in the northern hemisphere.