HSC vs public charging

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125mph

Member
Joined
Mar 15, 2021
Messages
20
My super off-peak electric rates is $0.09 / kWh so it makes charging cheap.

The public rates are like $0.43 /kWh which seems like it makes the car more expensive to drive than normal gas powered vehicles.

Is it more cost efficient to use the HSC when traveling past i3 range, or is it cheaper to stop by these fast chargers and pay the higher public rate? Anyone do some math on this before?
 
My math is as follows (though I don't have a REX):
The EPA says 33.7 kilowatt hours of electricity is equivalent to one gallon of gasoline. That means your cost for the same amount of energy as a gallon of gas is:
Home: 0.09$/kWh * 33.7kWh/"gal" = $ 3.03 $/"gal"
Away: 0.43$/kWh * 33.7kWh/"gal" = $14.49 $/"gal" Yikes.

But EVs don't waste most of their energy like gas cars do, so we can take efficiency into account to get a cost per mile:

The next part depends a little on which i3 REX you have, but I'll assume the 60ah battery.

With efficiency #s from here: https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=35279&id=38229&id=43745

It has an MPGe value of 117 so your cost per mile on electric is:
Home: 3.03$/gal / 117mi/gal = 0.0259 $/mi
Away: 14.49$/gal / 117mi/gal = 0.1239 $/mi

Multiplying by the rating of 39MPG while running on the REX and we get the break-even point of a gallon of gas running the petrol engine:
Home: 0.0259 $/mi * 39 mi/gal = 1.01 $/gal
Away: 0.1239 $/mi * 39 mi/gal = 4.83 $/gal

So, yes, if your gas is cheaper than $4.83/gallon, it'd be cheaper to run the REX than pay 43c/kWh.

If my logic is right, the 120ah i3 is less efficient with electricity (100 MPGe which is 85% as efficient as the 60ah) but even LESS efficient with gas (31mpg which is 79% as efficient as the 60ah), so this tips the scale in favor of public charging a bit

Home: ( 3.03$/gal / 100mi/gal) * 31mi/gal = 0.94 $/gal
Away: (14.49$/gal / 100mi/gal) * 31mi/gal = 4.49 $/gal

And because I did the other two, I don't want the 94ah to feel left out:
Home: ( 3.03$/gal / 111mi/gal) * 35mi/gal = 0.96 $/gal
Away: (14.49$/gal / 111mi/gal) * 35mi/gal = 4.57 $/gal

Now I just hope my math is right :)
 
Great analysis. I was calculating it as 33 kW (90Ah) battery gets me 85 miles and charging that battery costs:

At Home: 33 x .09 /kWh = $2.97
Away: 33 x 0.43 /kWH = $14.19

But then I didnt know how much gas cost it would run if I ran purely on gas. Looks like your math is good!
 
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