Electric Cars
The purpose of this section is to explore the specifications of several electric cars. (At the moment we have no software products related to this subject.)
The U.S. Department of Energy (DOE) and Environmental Protection Agency (EPA) host a web site, fueleconomy.gov, which has a database of fuel efficiencies for all cars sold in the United States. For electric cars, it uses the unit "MPGe" in place of miles per gallon, where MPGe is the efficiency in miles per 33.7 kWh (energy contained in one U.S. gallon of gasoline).
Electric Efficiency
Table 1 below compares efficiencies for several popular electric cars and two hybrids.
| Make | Model | EPA City MPGe | City Efficiency (mi/kWh) | EPA Highway MPGe | Highway Efficiency (mi/kWh) | EPA Combined MPGe | Combined Efficiency (mi/kWh) |
|---|---|---|---|---|---|---|---|
Note that city and highway MPGe numbers are not available for the Volt and Prius Prime, because they are both gasoline-electric hybrids and the EPA treats them differently. It provides combined city/highway gasoline-mode numbers instead: 42 MPG for the Volt and 54 MPG for the Prius.
The table shows several interesting things. The small mass of the carbon fiber BMW i3 60Ah appears to give it an advantage in the city. The BMW i3 94Ah loses efficiency to its 60Ah brother, which is somewhat surprising considering the very small difference in curb weight. The Bolt has good efficiency like the BMW i3 94Ah, yet it can travel more than twice as far on a charge. The highway efficiency of the Model S 60D compares quite favorably with the smaller cars, presumably because it has good aerodynamics and because the all-wheel-drive distributes the power intelligently. On the other hand, the boxy shape of the Soul EV appears to hurt its highway efficiency. The Prius Prime, although it is not a pure EV, has very good overall efficiency, likely due to good aerodynamics and small battery mass. Although the Volt can go more than twice as far as the Prius before its gasoline engine starts, it is significantly less efficient in both electric mode and gasoline mode.
Electric Range
Table 2 below compares electric ranges for the same set of cars. The non-EPA range columns, (City, Highway, and Combined), are calculated from EPA MPGe and estimated usable battery energy (kWh). Note that the resulting values are usually more pessimistic than the EPA ranges. This implies that the EPA uses different standards or scenarios for MPGe and range tests.
| Make | Model | EPA City MPGe | City Range1 (mi) | EPA Highway MPGe | Highway Range1 (mi) | EPA Combined MPGe | Comb. Range1 (mi) | EPA Range (mi) |
|---|---|---|---|---|---|---|---|---|
Notes:
1 BMW reports 18.8 kWh usable in the i3 60Ah.
2 GM reports 14 kWh usable in the Volt.
3 Internet review reports about 27 kWh usable for Soul 27kWh.
4 Wikipedia reports 21.3 kWh usable for Leaf 24kWh.
5 Level 2 station display implies about 6 kWh usable in the Prius Prime.
At the moment, the usable battery capacity for many of the cars in the table is unknown, so they show only EPA ranges.
This table contains some noteworthy information. The second i3 overtakes the second Leaf in range due to a larger jump in battery capacity. The Bolt has better range than the 60kWh Model S, even though the former is significantly less expensive. The Soul EV has better range than the i3 60Ah and Leaf 24kWh competition, because its larger battery overcomes efficiency disadvantages.
Chart 2 below compares the EPA range values in a more visual way.