Second napkin math for those that use an SUV…

In the vein of my earlier post comparing our ActiveE with our 328i.  Since it was time to fill up our 2001 X5 I figured it would be the time to compare the math vs. the math previously computed for the ActiveE.

Here’s the back of the napkin math. The fill up was for super unleaded at $4.239 per gallon (price of gas is dropping from the time I did the 328i comparison) and I filled up with 20.070 gallons for a total of $85.08. The range says 430 miles, since I zero out the odometer after each fill up, I know I did 358.4 miles since the last fill up. This is about 10 gallons of gas more than the last fill up (9.761 gallons previously).

So, I figure that my cost per mile (using Super Unleaded) is approx $0.2374 per mile.

As with the original calculations on the ActiveE, I’m heavily subsidized… I fill up at many locations where the electricity AND parking is free, the only place it costs to fill up is at home. I do about 35 miles each way to/from work and I charge for free 3/4 of a mile from the office, assuming 10 kWh of energy at home that I fill up and pay for on the average (some fill ups more, some less) to get me to full. I have yet to pay my Time of Use Tariff, so I’m defaulting to last month’s Domestic Tariff for Electricity, which tops off at $0.31 per kWh, so that’s $3.10 per day of fill up, 10kWh is about 1 day in 70 miles roundtrip…

So my electric cost per mile last month is approximately $0.0443 per mile.

So, 430 miles would run $21.71 vs. $102.07 on the X5… or 1/5th the cost of energy for the X5.  However, the X5 can fit a LOT of stuff vs. the ActiveE, so, it really is not a fair comparison.  Additionally, I use the two cars quite differently from the other.  However, I’ve found that shopping trips to Costco on the ActiveE is A LOT CHEAPER than with the X5 as it lowers the likelihood of impulse purchases of larger (both size and ticket) items.

Side note, Still waiting on the Time of Use bill, so I’ll update later when that comes up. But as I noted previously, I’m guessing that this new tariff drops my cost per kWh to between $0.10 to $0.16 per kWh (depending on Tier 1 or Tier 2 of usage). So, the next month’s cost will probably be closer to $0.0222 per mile.

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rEVolutionary armed with a Tesla Model S S85 and a Tesla Roadster, when his wife let's him borrow it. Formerly driving a BMW Active E (2012-Feb to 2014-Feb). Dennis has been driving EVs since he found himself on the BMW Active E trials on February 2012. As a result of his involvement in the Active E program, he became Accidentally Environmental. Aside from this blog, he often tweets @dennis_p. When not driving, he can be found on the following Tesla/EV forums -,, and as AEdennis or on as Dennis. In the interest of full disclosure, Dennis has an inherent bias toward electric vehicles and has an investment in and is LONG Tesla (NASDAQ: TSLA).

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