[aerohead]

Using simple average between the 'summer' and 'winter' energy consumption yields a 'seasonally-averaged' 570.85-Wh/mi.
* @ 63-mph, this yields 35,964.07 Wh/hr.
* converting to brake-horsepower yields 48.228-bhp-e.
* using the industry-average BTE-e of 95%, yields a Road Load of 45.228-hp.
* subtracting out the estimated 8.1312-hp rolling-resistance power absorption yields 37.685-hp aero power absorption.
* plugging into the aero power equation with the unaltering standard air, velocity, and Af, spits out a 'seasonally-averaged Cd 0.3174.
NOTE: Cd 0.3174 compares within 98.9% agreement with A. Gilhouse's Cd 0.314 simple wind tunnel model results, of 1981, for 'softened'-nose, roof edge radii, and rear radii, on a 'bus'/ 'motor coach.'
Qualitatively, the Gilhouse 'stromform'-nosed model of same features as the above model, could produce a Cd in the neighborhood of 0.294. The nose of this model better represents that of the ZEVO 600.
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If we take the more conservative Cd 0.3174, the target drag reduction of 20% would occur with a 'wake' area of 55.68 sq-feet, @ Cd 0.2539.