Comment by porphyra | Hacker News Reader

Comment by porphyra | Hacker News Reader

Parent Full thread

The Waymo I-Pace is much less efficient than the regular roadgoing I-Pace. One X user posted a pic of the dashboard of a Waymo with 111,000 miles on the odometer, and it averaged 1.0 kWh per mile [1][2]. This is about 2.5x worse than the EPA rating of a normal Jaguar I-Pace. Probably the difference is because the Waymo has tons of compute and the sensors have a surprisingly large impact on aerodynamic efficiency. I was being generous to the Waymo in my original comment. If we compare the actual rating of the Cybercab at 165 Wh per mile, it would be 6x as efficient.

Also, whereas the stock Jaguar I-Pace was $70k, the Waymo one with all its sensors and compute have estimates ranging from $150k to $200k. In a comment made in late 2024, Waymo CEO Dmitri Dolgov mentions that the sensors and compute themselves cost $100k [3].

> The equipment on Waymo’s fifth-generation robot taxis — electric Jaguar I-Pace vehicles — costs as much as $100,000, Dmitri Dolgov, Waymo’s co-chief executive, said on a podcast in February.

That is the same generation as the current I-Pace fleet that makes up the majority of Waymos.

[1] https://eletric-vehicles.com/waymo/waymos-retrofitted-robota...

[2] https://x.com/niccruzpatane/status/2073967445509882286?s=20

[3] https://www.nytimes.com/2024/09/04/technology/waymo-expansio...

Referring to the example from the Twitter post you cited, wouldn't the KWh per mile simply be a lot higher because these vehicles are engaging in much less efficient travel overall? City driving itself is often pretty inefficient because of all the stopping and going, and these vehicles likely are driving in a lot of the rush hour traffic and high density areas everyday. Not to mention they probably idle around a lot more than a normal persons car would in a day.

So wouldn't that be the reason the figures would look 2.5x worse than the regular Jaguar? I'm sure there are other factors of course since running the computer systems, lidar and all the other features will also consume more power, so I'm sure from a baseline it will be less efficient anyway, I just think because of the kind of driving it engages in, this will make it also look far less efficient.

Possible, but EVs tend to be more efficient in city driving than highway driving, thanks to regenerative braking and the fact that the dominant form of energy loss, air resistance, scales quadratically with speed.

Depending on conditions, heat or AC can consume up to 5 or 6 kW in extreme weather and a small fraction of that in milder conditions. The most efficient speed of an EV is hard to pin down. If all fixed loads could be turned off, it would be most efficient at the slowest possible speed but with HVAC and compute loads present, the most efficient speed is around where the aerodynamic load is equal to the fixed load. That's still likely to be rather slow but the idealized math that gives this optimum is for steady-state operation. There is a round-trip loss for regen, so there is still an advantage to steady operation even if it is not as big as with ICE cars where no kinetic energy is recovered.

My guess for the poor reported number is excessive idle time w/ HVAC and compute stuff on within the trip interval.

Weather can be arbitrarily extreme, but:

1. My whole house AC only consumes 3 kW when the outside is really hot, like 36 degrees C, and I seriously doubt that car AC can consume 5 or 6 kW

2. With hotter weather, the density of air also decreases and air resistance is reduced. This partially offsets the need for extra cooling (of both the occupants and the battery), so range is only perhaps impacted by 5-10%.

Max power consumption of the compressor in my car is 5.5 kW (see pg. 28 of https://www.scribd.com/document/783343319/MEB-220169869). The blowers would draw additional power. These values would only be hit in extremes and I'm not certain the compressor can run at 100% duty cycle.

Regarding the dashboard pic - that's a trip computer display (see the "A:" and https://www.youtube.com/watch?v=hAdzIuAB3-g) which can display a large range of values depending on the history since the trip was last reset. That fact is recognized in the article you posted but buried in the middle. Using the power estimates in the article won't get you to the inefficiency shown in the trip computer either and aerodynamic changes only make sense if the vehicle is making mostly highway trips, which maybe? My EV, less efficient than the i-Pace (because it's big tall van), in it's first 10k miles averaged 2.5 mi/kWh or 0.4 kWh/mile at an average speed of 36 mph. That works out to around 14.4 kW average load. Adding 3 kW to that for compute (upper end of estimate of one source in the article you linked) pushes that number to 17.4 kW, which would change my efficiency number to 2.1 miles/kWh - still double the i-Pace trip computer. So I don't trust that number as a foundation for any conclusions.

And if the cybercab is cheaper because it doesn't include the sensors needed to actually see the world around it, that's not great either.

Reply on news.ycombinator.com