[Speculation] Model 3 0.237 kwh/mile!

[KarenRei]

The most efficient EV on the road by a significant margin per EPA ratings is the Hyundia Ioniq EV with an EPA-combined rating of 250 Wh/mile. It has a curbweight of only 3,164 lbs.
2017 Hyundai Ioniq Electric

I have a hard time imagining the significantly-heavier* (*assumed) Model 3 beating that. If it does, I will be very impressed.

I wouldn't assume "significantly". If it's a 50kWh pack (which you'd expect for the stated range with that sort of energy consumption), then the pack is (roughly) 2/3rds the weight of a S 75 pack. The car is steel + alumimum rather than just aluminum, but it's smaller, too. The P75 is 2000kg. I'm thinking 1700kg. Versus a 1435kg Ioniq EV, that's 18% more weight. At highway speeds, that's something like an 6% higher rolling drag for the Model 3. Ioniq's drag coefficient is 0,24, 14% higher than the design goal of 0,21 for the Model 3. So about 10% more highway drag on the Ioniq per unit cross section. So the Model 3 should use less energy than the Ioniq if the cross sections are the same. The real question is, what is the cross section? Also, what's the actual achieved drag coefficient? CdA is what really matters, not Crr.

But, more likely it seems that if 237 Wh/mile is a number of any real significance, it would be the battery-to-wheels energy consumption.

Except that the other numbers are clearly wall-to-wheels.

I'm tempted to go with EchoDelta's notion that it's just a made-up filler number.... but if so, that's an awfully specific filler number.

Just... very curious.

 

[Esme Es Mejor]

Man that would be fantastic. That's only slightly less than my average of 4.7 m/kWh that I get on my little leaf. That's 4.2 m/kWh... really nice.

-Jim

I got 4.3m/kWH during my first 2000 miles driving the Leaf. I've bumped that up to 5.4m/kWH over the last 1600 miles. I could do even better, but I love blowing ICE cars off the line, even with a very underpowered EV.

 

[JeffK]

This speculation is pretty much spot on with my expectations. My math has always come up somewhere between 4.1 and 4.3 miles / kWh.

 

[scaesare]

Yes it absolutely does. You need more of the energy stored chemically in the cell to propel the car forward. This is what the car does when it moves. Converts chemical energy to forward motion. It does not matter where in that process power was utilized, including heating the battery from resistive losses or chemically degrading the cell.

Where do you think the car measures the power it consumes?

 

[Yggdrasill]

Where do you think the car measures the power it consumes?

At what current draw do you think the capacity of the pack has been specified?

Driving really carefully with a 85 kWh pack, you can get out 77 kWh. That can drop to something like 70 kWh if you're at the track. With higher average power consumption, more energy is lost as heat in the battery.

 

[SageBrush]

At what current draw do you think the capacity of the pack has been specified?

epa cycle

 

[JeffK]

IR is power lost at the cell level. That effectively diminishes what energy the cell can deliver. It does not change the power the car needs to move a mile.

Yes it absolutely does. You need more of the energy stored chemically in the cell to propel the car forward. This is what the car does when it moves. Converts chemical energy to forward motion. It does not matter where in that process power was utilized, including heating the battery from resistive losses or chemically degrading the cell.

There's a but of a mixup between power and energy.

The energy needed to move a car from point A to B through the motor might be the same, but total energy used from the battery might be higher if there are higher losses. Hope that makes sense.

 

[Yggdrasill]

epa cycle

No way. Probably 1/4C, maybe just 1/10C.

 

[SageBrush]

I'm thinking 1700kg. Versus a 1435kg Ioniq EV, that's 18% more weight. At highway speeds, that's something like an 6% higher rolling drag for the Model 3.

You lost me here. Rolling friction is not related to car speed, and in the case you me mention is worth about 6 Wh/km more in the Model 3

 

[KarenRei]

You lost me here. Rolling friction is not related to car speed, and in the case you me mention is worth about 10 Wh/km more in the Model 3

Sorry, phrased poorly. 6% more total drag, not 6% more rolling drag. Because at highway speeds rolling drag is a relatively small fraction of total drag.

 

[SageBrush]

Sorry, phrased poorly. 6% more total drag, not 6% more rolling drag. Because at highway speeds rolling drag is a relatively small fraction of total drag.

I recalculated. The difference in mass using your numbers is 7.7 Wh/km more for the Model 3 at ~ 105 kph (65 mph.) Since we know that total energy/km is going to be in middlish 225 - 275 Wh/mile range (140 - 170 Wh/km), the penalty from the larger mass is around 5%. That compares quite nicely with the 15% lower Cd on the highway where it matters.

 

[KarenRei]

Yes, the (presumed) lower Cd is much more significant than the (presumed) higher mass Frontal area is the big unknown, of course.

 

[JeffK]

This leads to the effects of the aero wheels.

 

[LargeHamCollider]

You lost me here. Rolling friction is not related to car speed, and in the case you me mention is worth about 6 Wh/km more in the Model 3

Rolling friction actually is related to velocity, but it's a pretty weak relationship until above 100mph, especially at high tire pressures.

 

[SageBrush]

Rolling friction actually is related to velocity, but it's a pretty weak relationship until above 100mph, especially at high tire pressures.

I refuse to listen to anything not taught in my freshman college level physics ;-)

 

[EchoDelta]

Offtopic: Took 15 mins to look at the site myself , didn't glean anything new.
All sorts of fun stuff thrown in there.. omg what a drupal hell it must be to maintain it.
and ... high five to whoever added that "lorem ipsum sit amet dolor con carne roja y papas diablos" ¯\_(ツ)_/¯

 

[SageBrush]

Offtopic: Took 15 mins to look at the site myself , didn't glean anything new.
All sorts of fun stuff thrown in there.. omg what a drupal hell it must be to maintain it.
and ... high five to whoever added that "lorem ipsum sit amet dolor con carne roja y papas diablos" ¯\_(ツ)_/¯

Loosely translated, the coder was hungry

 

[scaesare]

At what current draw do you think the capacity of the pack has been specified?

Driving really carefully with a 85 kWh pack, you can get out 77 kWh. That can drop to something like 70 kWh if you're at the track. With higher average power consumption, more energy is lost as heat in the battery.

Your questions supports my point.

The issue is how much the pack can supply is affected by IR. Hence all ratings age "nominal".

This is a different metric to how much energy the car draws for locomotive force.

 

[KarenRei]

Rolling friction actually is related to velocity, but it's a pretty weak relationship until above 100mph, especially at high tire pressures.

Haha, if we want to get into the nitty gritty, I could recommend a good paper on modeling the imparted rolling resistance from driving through snow of different densities and depths....

Tire rolling resistance, tire temperature, tire pressure, tire wear, cornering, road MPD (mean profile depth), road IRI (international roughness index)..... so many factors come into play

 

[SageBrush]

Yes, the (presumed) lower Cd is much more significant than the (presumed) higher mass Frontal area is the big unknown, of course.

I played around with this a little more using

Ioniq: 1435 Kg
........Cd: 0.24

Model 3: 1800 Kg
.......... Cd: 0.21

Frontal Area presumed the same.

At 110 kph the Model 3 uses 32 N more due to weight and 67 N less in Aero, for a net reduction of ~ 10 Wh/km

Addendum: Sorry, I used a different frontal area for the Hyundai above. At the same frontal area the Model 3 has a 2 Wh/km advantage at 110 kph between Cd and mass.