Running on grid power, as it will almost surely do for far more than half its miles, the 2014 BMW i3 is a remarkably efficient electric car. While its EPA range rating is average--at 81 miles--it is the most efficient car sold in the U.S. this year, rated at 124 MPGe. (The unit measures the distance a car can cover using the same amount of energy from its battery as is contained in 1 gallon of gasoline.) The i3's light weight, purpose-built construction, and dedicated drivetrain have all been optimized around the goal of extracting maximum distance from every stored electron. And it works.
Because electric cars are still a novelty in the U.S., we rate every battery-electric vehicle at 10 on our Green scale. Relative efficiency differences among electric cars are less important than the fact that they run on grid power--which automatically makes them some of the greenest cars you can buy.
And even if a BMW i3 is recharged from the oldest, dirtiest coal power plants in the nation, it remains cleaner--comparing "wells-to-wheels" carbon emitted through the process of creating the fuel as well as powering the car--than any gasoline car sold today that isn't a hybrid. In California, which will see more plug-in sales than the next five states combined, the grid is relatively clean, so parity with any gasoline car soars toward unattainable numbers like 80 or 90 mpg.
The BMW i3 is far from the lowest-priced electric car on the market, but like all plug-ins, its running cost per mile will be very low against gasoline or diesel cars. At average U.S. electricity prices, it's likely to cost about one-quarter as much to run 100 miles as a 25-mpg gasoline car. But that difference varies quite a lot, because electricity prices per kilowatt-hour cover a much wider range than gasoline or diesel fuel costs--so your cost efficiency may vary.
With a built-in charger capable of up to 7.4 kilowatts (higher even than the 6.6-kW units found in the Nissan Leaf and other cars), the BMW i3 can recharge its battery pack to 80 percent of capacity or more in under 4 hours using BMW's 240-volt Level 2 charging station--and about 20 percent longer using Level 2 stations from other makers. Those stations may require some home electrical work, but no more than what's needed to install an electric stove or clothes drier.
On standard 110-volt household current, a full recharge will take four times or more that long. BMW does not offer an option to charge only to 80 percent of capacity, however, as Tesla and Nissan do; the company said it wanted to reduce complexity for its customers. The i3 will also offer a DC quick-charging port compatible with the new Combined Charging Standard (CCS) protocol--although today there are very few stations using that standard.