2014 BMW i3: Less Than Two Gallons of Gas In Two Months
June 3, 2015
It's really difficult to track the electricity and gasoline consumption of our 2014 BMW i3 to the nth degree. The vast majority of public charge stations in the wild lack displays that reveal the number of kilowatt-hours (kWh) of electricity dispensed during a charge. And it's not easy to remember to manually record the trip odometer when our i3 runs out of juice and switches from electricity to gasoline. Both are crucial bits of information.
The first part is hard to deal with. We try to charge at Chargepoint stations as much as possible since we own one of their units and can look up our charging activity anywhere on their network in our account. But there are times when we have to charge at Brand X stations, and those times earn a blank line in our logsheet.
The second problem is one of muscle memory. It's easy to forget because: (a) you're driving when the switchover happens and; (b) 65 miles of electric range is enough that we don't run into gasoline mode very often. Exactly how rare are the visits from the range extender? It came to life just three times over a recent two-month period (February 23-April 23), and 1,709 miles of travel.
During that time we filled up exactly once and added 1.722 gallons of gasoline.
On the face of it, that works out to 992.5 mpg. But who's kidding who? The bulk of those miles were electric ones.
How many? It just so happens that all three switchover points were properly captured. We can say with confidence that during that two-month period, we ran 1,656.6 miles on electricity and 52.4 miles on gasoline.
Using 52.4 miles instead, our 1.722 gallons of gasoline burned at a rate of 30.4 mpg. The EPA's fuel economy rating for the i3 range-extender (REX) is 39 mpg. Sure, we fell short, but when only 1.722 gallons are involved, the over-consumption amounts to just 0.38 gallons. That's less than $1.50 over two months. I lose that much loose change in couch cushions.
Our 1,656.6 miles of electric driving consumed 468 kWh, which works out to an average electricity consumption rate of 28.2 kWh per 100 miles. The i3's EPA electricity consumption rating is 29 kWh/100 miles, so we're doing better than predicted here. Thing is, our driving style was the same on electricity and gasoline.
Those electric miles were spread across 44 different plug-in events. On average, each charge consumed 10.64 kWh after spending 37.7 miles on the road.
Our maximum observed electric range in this period was 67.5 miles, but there were only three such max-range events. Each required an average of 20.5 kWh to refill the battery (minimum 19.79 kWh, maximum 21.5 kWh)
Utility Factor is a number applied to plug-in hybrids and electric vehicles with a range extender like ours. It's the predicted percentage of total miles run on electricity, and as you might expect, the bigger the electric range, the higher the utility factor.
With 1,656.6 miles out of 1,709 run on electricity, our Utility Factor during the two-month period was 96.9 percent. I have a Utility Factory chart published by the Society of Automotive Engineers some years ago which suggests that a range-extender EV with 72 miles of rated range will run on electricity 80 percent of the time. We crushed it during our two-month period.
I'm still going over the data for the miles added since then, but it's very clear that our i3 REX has enough electric range to run as an EV a very high percentage of the time. It's only those staffers with long commutes, such as yours truly, that tend to run it down to where the gasoline engine fires up.
Dan Edmunds, Director of Vehicle Testing @ 1,519 miles