EV efficiency

I captured a screen shot from www.fueleconomy.gov list of 24 electric vehicles:

	model	MPGe	City	Hwy	kWh/100 mi
1	Hyundai Ioniq Electric	136	150	122	25
2	Tesla Model 3 Long Range	130	136	123	26
3	Chevrolet Bolt EV	119	128	110	28
4	Volkswagen e-Golf	119	126	111	28
5	BMW i3 (94Ah)	118	129	106	29
6	Tesla Model 3 Long Range AWD Performance	116	120	112	29
7	Tesla Model 3 Long Range AWD	116	120	112	29
8	Honda Clarity EV	114	126	103	30
9	BMW i3s (94Ah)	112	126	99	30
10	Nissan Leaf	112	125	100	30
11	Fiat 500e	112	121	103	30
12	smart fortwo electric drive coupe	108	124	94	31
13	Kia Soul Electric	108	124	93	31
14	Ford Focus Electric	107	118	96	31
15	Tesla Model S 75D	103	102	105	33
16	smart fortwo electric drive convertible	102	112	91	33
17	Tesla Model S 100D	102	101	102	33
18	Tesla Model S 75kWh	98	97	100	34
19	Tesla Model S P100D	98	92	105	35
20	Tesla Model X 75D	93	91	95	36
21	Tesla Model X 100D	87	86	89	39
22	Tesla Model X P100D	85	83	89	40
23	BYD e6	72	73	71	47

• Caution with the Hyundai as we are seeing a significant gap between the user reported, hybrid mileage in Fuelly,com and the EPA numbers. I left it in the table even though I have some reservations.
• Notice the Tesla Model 3 is significantly improved over the Model S and X. In effect a clean-sheet, optimized design.

Bob Wilson

 

So I defined a new term:

• City Eff = (MPGe_City - MPGe_Hwy) / (MPGe_City + MPGe_Hwy)

A higher number means the vehicle is better around town, ~90% of our miles, versus highway. Realize that high City Eff could be due to poor aerodynamics:

	model	City	Hwy	City Eff %
1	Kia Soul Electric	124	93	14.3%
2	smart fortwo electric drive coupe	124	94	13.8%
3	BMW i3s (94Ah)	126	99	12.0%
4	Nissan Leaf	125	100	11.1%
5	smart fortwo electric drive convertible	112	91	10.3%
6	Hyundai Ioniq Electric	150	122	10.3%
7	Ford Focus Electric	118	96	10.3%
8	Honda Clarity EV	126	103	10.0%
9	BMW i3 (94Ah)	129	106	9.8%
10	Fiat 500e	121	103	8.0%
11	Chevrolet Bolt EV	128	110	7.6%
12	Volkswagen e-Golf	126	111	6.3%
13	Tesla Model 3 Long Range	136	123	5.0%
14	Tesla Model 3 Long Range AWD Performance	120	112	3.4%
15	Tesla Model 3 Long Range AWD	120	112	3.4%
16	BYD e6	73	71	1.4%
17	Tesla Model S 100D	101	102	-0.5%
18	Tesla Model S 75D	102	105	-1.4%
19	Tesla Model S 75kWh	97	100	-1.5%
20	Tesla Model X 100D	86	89	-1.7%
21	Tesla Model X 75D	91	95	-2.2%
22	Tesla Model X P100D	83	89	-3.5%
23	Tesla Model S P100D	92	105	-6.6%

In a graph:

• Induction motors are less efficient than PM but affordable when the Model S and X came out. There are reports of overheating at sustained high speeds and this is also consistent with induction motor inefficiencies. Also, the AWD Model 3 uses an induction motor for the front so with balanced power, the lower City efficiency makes sense.
• Back when the Model S and X came out, power electronics were silicon based. But today Tesla has access (reports are) silicon-carbide, power electronics. These are more efficient.
• Tesla changed from the 18650 to 2170 that uses a better geometry and chemistry.
• Notice the curious point for the Hyundai Ioniq EV . . . I still don't trust their data.
• The less efficient City cars look boxy, poor aerodynamics. At slow City speeds, aerodynamics are not so important.

Bob Wilson