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Sunday, May 12, 2013

Take that, Exxon!: EV insights, Day 12

So, I've been out of town for most of the past week, but want to set down a few more thoughts while they are fresh. At this point, the mileage numbers since our EV arrived April 30 look like this:

EV: 367
Prius: 147

Not quite the 80 percent I was hoping for (71.4 percent), and I'm sure that was a little unrealistic. Still, the improvement over our previous transportation mix (two hybrids, one getting 50 mpg and the other 40 mpg) is obvious:

Previous: 514 miles, average 45 mpg = 11.4 gallons of gasoline
Current: 514 miles, 147 fueled by gasoline, average 50 mpg = 2.9 gallons

Another way to put it: we've gone from averaging 45 mpg to averaging almost 175 mpg (514 divided by 2.9), which I think is pretty cool. That in turn leads to the conclusion that the  mpge (miles per gallon of gasoline equivalent) rating doesn't tell the whole story. The mpge rating emphasizes that the EV is still consuming energy (certainly important to keep in mind), but doesn't communicate the full benefits in terms of gasoline use.  While the MiEV's mpge rating is 112, its actual mpg is, of course, infinity, and our average mpg is limited only by how many miles we can load onto it.

Yesterday, we fulfilled one of the basic MiEV battery requirements--a fairly deep discharge. The manufacturer advises driving it until the fuel gauge drops below two bars and then recharging it fully. After two trips Friday and charging overnight, its range indicator read 55 miles.  Two more trips yesterday took it down to 19, and then I drove it enough to take it to two bars (12 or 13 miles on the indicator) and then home.  It was exciting!  We live on the side of a hill, and the range indicator drops steadily when driving uphill.  The refuel warning was flashing steadily and I had visions of falling a few hundred yards short, which would have been a minor disaster. In the end, I eased it into the garage with 5 miles still on the indicator.  Whew.  Won't be doing THAT again anytime soon (the manufacturer says it needs doing every two years).

Some additional stats:

367 miles on the EV, fuel savings 4.5 cents/mile = total savings to date $16.51 (not too impressive, but we traded in a 40-mpg hybrid--if you replace a 20-mpg auto, the savings would be 9 cents/mile). For the fuel savings calculation, see this previous post.

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