Report from recent March break family trip to cottage with 120V outside outlet available for charging.
Summary : Tesla 2x cheaper to "fuel" even in worse case conditions compared to gas SUV.
Efficiency on average speed 90 km/h, some 4xx series highway at >>100km/h, rest on non-divided roads at 80 km/h.
Distance ~200 km.
Temperature -13C at destination.
2013 Tesla Model S used ~65% battery for the 200 km driven.
This compares against 414 km "rated" (aka EPA) range of a fully charged battery (as reported on charging screen).
This means, as compared to EPA testing, driving the Tesla in cold winter weather uses approximately 30% more energy than the EPA test requires on average.
Charging on 120V partially refilled battery, adding 30% over the span of a few days, 29 hours of charging as reported in "Fleet Carma" device portal. Charging slowly uses far more energy than charging quickly due to the fact the battery charging and management systems are active (drawing energy for computers and other things) for a long period of time. This is a situation where charging efficiency is lower than it would be compared to charging on 240V (and obviously supercharging).
29 hours of charging on regular 12A plug was 42 kWh of energy consumed according to Fleet Carma.
With the off peak and mid peak prices this is ~$6.
$6 to add 90 km of range in winter on slow charging, with poor charging efficiency, battery heating due to cold (-13C) reducing amount of range added, off and mid peak electricity, pretty much worst case we've ever seen for "cost per km driven".
In comparison, our previous Mercedes SUV was 14L/100 km, so about double the cost to drive in similar conditions in terms of fuel.