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Comment by adrianN | Hacker News Reader

How much room for improvement is left on the consumption side? Electric cars seem to require around 15-20kWh/100km. Can we get that below 10 for regular highway driving, say at 130km/h? What are the numbers for city driving like?

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> Can we get that below 10 for regular highway driving

Mercedes did in the Vision EQXX:

https://www.autocar.co.uk/car-news/new-cars/mercedes-benz-vi...

https://www.cnet.com/roadshow/news/mercedes-vision-eqxx-ev-c...

https://www.youtube.com/watch?v=BS1SBhBjAHY

15-20kWh/100km is a gasoline equivalent of about 1,5-2l/100km. At 130km/h there is little room for improvement (thinner wheels, better aerodynamics). All the individual electric components in the car are like ~98% efficient.

I guess 10kWh/100km is possible at 90km/h on cruisecontroll behind a big truck.

EVs biggest problem are the inefficiencies in the electric grid, there is like a 50% margin for improvement.

You can make a self driving truck/electric vehicle lane where the speed limit is 80km/h. Paint a green line in the middle of the ev-lane and it should make self driving more easy to implement. Reason for slower speed wind resistance is far less at 80km/h. Energy use is quadratic concerning speed. So make a movie streaming ev-lane.

Also one could fit cars with rail gear and run them on rail tracks on the highway which would lessen the tire friction roll resistance losses. Technology for allowing cars to run on rail tracks already exists for railway maintenance cars. Self driving on rail track is also much easier to implement.

https://en.m.wikipedia.org/wiki/Road–rail_vehicle

Safety from car crashes would also be far safer at 80km/h than higher speeds.

Before you put them on rails, it might be easier to add panthographs to charge from overhead wires while driving in electric lane.

Germany has a short section of highway testing that setup for trucks

https://www.sustainabletruckvan.com/pantographs-for-trucks-s...

If people wanted to travel 80km/h they could do so today. It is well known that going slower improves fuel efficiency. I'm asking for things like improved drivetrain efficiency and better aerodynamics.

The laws of physics inconveniently get in the way.

If your 90% efficient drivetrain-tyre system uses 20 kWh per 100 km, then improving that to 95% efficient maybe reduces that to 17 kWh.

Pencils and javelins have lower drag coefficients than cars. Unfortunately people don't fit inside them. A javelin-shaped vehicle big enough to fit a person comfortably inside is a train.

> A javelin-shaped vehicle big enough to fit a person comfortably inside is a train.

or a cybertruck.

I don't mind going at 80 kmh if someone else is doing the driving.

Self driving on open roads where 80km/h is possible is basically a solved problem.

And if people cared about efficiency enough to drive at 80 they'd do it now. Low efficiency stsrt/stop driving is the problem to solve.

I like to drive a little slower to conserve charge/fuel, but it would be too discourteous to all the other drivers on the road, so I just go at the prevailing speed. If there were a separate lane for lower speed driving I would use it.

If it's a self driving only lane, the speed limit should be increased, not decreased. Self driving on a highway where all the cars are self driving is already a solved problem.

> Can we get that below 10 for regular highway driving, say at 130km/h?

Probably not with normal-sized cars.

For the Model 3, the theoretical minimum is 13.8 kW. This increases linearly with drag coefficient and area (as seen from the front). You would have to build a significantly smaller (flatter, narrower) car and improve the drag coefficient (0.2 has been achieved) to get there.

Here's a calculator in German (sorry) for experiments: http://spare-benzin.de/Fahrphysik/Luftwiderstand/Luftwiderst...

The Light-year zero is so efficient that it can gain 70km per day from its rooftop solar panels:

https://lightyear.one/lightyear-0

Initial model is > $300k but they plan a $30k model in the future.

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