comments:
There is a lot of bad information being thrown around in here. Right off the rip, you can't go by miles alone. If they're conditioning the cabin before they leave, while plugged in, that is energy being used that has zero impact on miles driven. 20% of our energy usage from our EVSE in the winter is just pre-heating the cabin. Miles driven also doesn't take into account their driving style, nor the tires on the car. Drive it like grandma? It's going to get better efficiency. Drive it like you stole it? You can easily cut a EV's efficiency in half. Put non-OE tires on it? It's not uncommon to see a 10-20% decrease in efficiency. Mileage also doesn't take in to account any battery conditioning that may be happening. Nor does it take in to account the weather. Our winter efficiency can be 50% of our summer efficiency, even with conservative heat use in the car. 2 weeks ago we did a quick 140 mile trip (70 each way, nearly all highway), returning home with a 1.9mi/kwh average. That is half of what we see in the summer and still lower than our 'typical' winter driving. 75mph, at night, when it's the coldest leads to significantly different efficiency than had we done 140 miles around town on the same day, during the day. The only legitimate way to track real world costs is to have them get a EVSE that tracks consumption from the wall. Then it doesn't matter how efficient or inefficient they're driving, how much they're pre-heating or cooling the cabin, battery conditioning, etc. A relatively inexpensive inline energy monitor like this one will track actual kwh usage. There are dozens of wifi connected EVSE's on Amazon available for $120-200 that will also track usage. Once you know what they're using in kwh every month, multiply that figure by your $0.112/kwh electric rate and that is the cost they pay.