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.


Show distances in kilometers (Table 1)
Make Model EPA City MPGe City Efficiency (mi/kWh) EPA Highway MPGe Highway Efficiency (mi/kWh) EPA Combined MPGe Combined Efficiency (mi/kWh)
BMW i3 BEV 60Ah 137 111 124
BMW i3 BEV 94Ah 129 106 118
Chevrolet Bolt 128 110 119
Chevrolet Volt - - - - 106
Kia Soul EV 120 92 105
Nissan Leaf 24kWh 126 101 114
Nissan Leaf 30kWh 124 101 112
Tesla Model S
60
98 101 99
Tesla Model S
60D
101 107 104
Toyota Prius Prime - - - - 133
Table 1: Combined Efficiency Comparison

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.


Show distances in kilometers (Chart 1)


Chart 1: Combined Efficiency Comparison

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.


Show distances in kilometers (Table 2)
Make Model EPA City MPGe City Range1 (mi) EPA Highway MPGe Highway Range1 (mi) EPA Combined MPGe Comb. Range1 (mi) EPA Range (mi)
BMW i3 BEV 60Ah 1 137 111 124 81
BMW i3 BEV 94Ah 129 - 106 - 118 - 114
Chevrolet Bolt 128 - 110 - 119 - 238
Chevrolet Volt 2 - - - - 106 - 53
Kia Soul EV 3 120 92 105 93
Nissan Leaf 24kWh4 126 101 114 84
Nissan Leaf 30kWh 124 - 101 - 112 - 107
Tesla Model S
60
98 - 101 - 99 - 210
Tesla Model S
60D
101 - 107 - 104 - 218
Toyota Prius Prime 5 - - - - 133 25
Table 2: Electric Range Comparison

Notes:

1 BMW reports 18.8 kWh usable.

2 GM reports 14 kWh usable.

3 Internet review reports about 27 kWh usable.

4 Wikipedia reports 21.3 kWh usable.

5 Level 2 station display implies about 6 kWh usable.


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.


Show distances in kilometers (Chart 2)


Chart 2: EPA Electric Range Comparison