(EDIT: I just realized that parent already touched on some of this.)
On the flip side, trailers spend more time parked at warehouses where they can charge leisurely.
Eliminating the need for fast charging could extend battery life or even allow for the use of cheaper battery technologies. Maybe we'll even see a future where the tractor draws most of its power from the trailer.
Then there's the other things you could do with a trailer that has always-on power. Climate control and realtime GPS tracking (and other telemetry) come to mind.
On the other hand, these things see a lot more annual miles than consumer vehicles so the payback period should be shorter. I agree though, that probably it would require some kind of government involvement to get broad adoption.
Also, I imagine it's easier to find extra space for batteries in the the trailer than the tractor.
Regenerative breaking seems like a more important improvement though.
Good point re: microeconomics between truck and trailer owners.
The trailers could also charge off the alternator of the truck itself which could help to calm concerns of long charging times at stationary sources. The percent gains would probably be in the single digits and would demand a bit more from the engine but maybe there's an optimal balance there.
An alternator is about 50% efficient. The engine turning the alternator is around 40% efficient. So charging a battery using your engine doesn't really pay off.
If you optimize for a more efficient Regen using a proper purpose driven 'alternator', and only do it when the truck is slowing down, that would be much better. Aka, current hybrid tech.
Good points. It would be a productive use of all of the time those trucks spend idling too, going into and out of ports and in freeway traffic. Seems like there are times and circumstances when directing excess diesel energy to the trailer battery could be reasonable.
There is no such thing as excess diesel energy.
If today an idling diesel engine uses n units of fuel per minute, if you try to put any power into a battery for use later, it will use more n+x fuel per minute.
Now, if for some reason the engine was idling for no reason other than to keep a dome light on for an hour, then yes you could generate 100 watts as fast as possible and then turn the entire engine off, leaving the dome light lit for several hours off that 100watts you made. That is what a current hybrid does, again.
But if the engine has to idle for other reasons, even laziness, making power while it idles is simply using extra fuel to make that power.
It probably isn’t worth charging the trailer from the truck. The truck would be capable of towing with an empty trailer battery anyway. Burning extra diesel to charge the battery is usually going to be less efficient than just using that diesel to go down the road.
The trailer can charge next time you need to slow down or go down a hill and engage the regen braking.
Interesting. At what point might it make sense for the tractor itself to evolve into a pure genset and steering unit, like a diesel-electric train? Might make sense as an interim step to carbon-free electrification.
Yeah, this was my thought as well. Not sure how accurate this article[0] is, but it says the trailer to power-unit(tractor) ratio is around 3-5:1.
One interesting thought though: if these trailers could implement thrust vectoring and other safety measures(like adjacent vehicle detection), it may be realistic to run longer trains than can be done with dumb trailers that tend to be unhandleable beyond 2-long. This may effect a reduction in the trailer pool ratio, increasing efficiency even more.
I grew up in the Columbia River gorge and I remember driving alongside triple-trailer pulls and it was terrifying to attempt passing them when the wind was gusty. I'm confident everyone that frequented that corridor could regale you with tales of being almost run off the road by one of these behemoths at least once.
Have you ever heard about "road trains" in Australia? We have some truly absurd allowances for how long these vehicles can get. It makes driving between capital cities a wild experience, trying to pass them (they're almost as bad as the suicidal kangaroos that jump in front of cars at night)
Also depending on the type of operation, the trailer owner may not care about how much diesel the truck owner burns.
One benefit though is that the trailers could slow charge off of a basic 240V charger while parked at a loading dock between uses.