220 volt charging with my clipper creek EVSE is at 20 amps and that is 4.8kwh so I charge my i3 in about 5 hours from empty. So it saves me 14 hrs from empty. Thus the calculator reduces the gas usage due to the shorter recharging time. I could have opted for a 30 amp EVSE and that would have resulted in a 3.5 hr charging time from empty, but I would have had to put in a new 220 volt supply to my garage at the higher 30 amp rating. For me 5 hrs was ok and therefore I used what i had available.
