Range Energy's electric trailer can improve semi-truck mpg by 36% | Hacker News Reader

Range Energy's electric trailer can improve semi-truck mpg by 36%

electrek.co

79 pointsthelastgallon32 comments

A very similar concept is Revoy, which hitches a device between the tractor and trailer. I expect Revoy's model would see a much higher utilization rate (time spent driving or charging vs sitting idle).

https://www.revoy.com/

This seems like a neat idea. But it looks like it also adds an extra pivot point and length. Are most commercial drivers trained to handle these and would they normally have the proper endorsements for such trailers?

That was my thinking as well, in Australia this would be a b-double tandem, requiring extra endorsement (multi-combination license).

The article writer claims that the market for this will disappear as more electric trucks enter the market and I couldn't disagree more, it will make them MORE desirable.

The biggest issue with electric trucks is range, and it's way more of a problem than it is with cars. Charging a truck in 20 minutes is a very different beast from doing it with a car since the amount of power needed is much higher, potentially in the tens of megawatts. Trucks are also traveling very long distances every day instead of just on the occasional road trip. If having a trailer assist is the difference between getting to your destination in one go vs stopping that's way more important for a truck than a car.

If a truck can effectively get a 30% charge just from picking up a trailer then that's massive.

You could do that with a much simpler trailer, though. All you need is battery and a cable.

I don't know anything about electric trucks, but given that the standard use is to add trailers to them, I'd be surprised if "put the battery in the trailer" isn't already part of the plan.

The battery is already a huge chunk of the cost, the added benefit of putting traction on the trailer itself is pretty big and could theoretically allow trucks to exceed their rated towing capacity if regulators get on it.

Also it means that it's compatible with ALL trucks, not just electric ones, and doesn't rely on truck manufacturers integrating a new standard power supply that can be used while the truck is moving.

Doing so would lose out on a large amount of regen though. If you are putting electric motors on the trailer axles anyways to capture the energy which would normally be turned into heat in the trailer brakes, then you may as well also drive those axles to make the most of the weight.

Perhaps this means the tractors can be less powerful if most trailers also provide some motive power.

There are limits to the total weight a truck is allowed to carry per axle and in total gross weight (see table half way down):

https://cowtownexpress.com/blog/legal-axle-weight-limits-for...

A battery-electric trailer will cut into the available (legally limited) 80,000 lbs gross vehicle weight. Which means truckers will not be able to carry a full load.

Not sure how the math works out when you save fuel yet can't deliver a full load, which is what you get paid to deliver.

I doubt every single truck load is packed to the maximum allowed weight. There must be a ton of shipping thats less dense.

A quick look reveals that, while this is true, the industry wants to achieve full load factor due to economics. What surprised me was to learn that up to 35% of trucks on the road are empty. Also, companies like Home Depot, Amazon, Walmart, etc., who have more control over the loading of their trucks regularly achieve 85% load factor.

I think this is a potentially interesting question. If 85% load factor means that it would be safe to add 12,000 lbs to a trailer to electrify it, the exercise might make sense.

The bottom line is that the economics and the logistics have to make sense. I don't know enough about the combination to have a valid opinion one way or the other. The only thing I can say is that, more often than not, things that sound good on first inspection fail to survive contact with reality.

For example: The fleet of non-electrified trailers are simple and inexpensive when compared to electric trailers with 200 kWh in batteries, powerful motors and all that goes with that transition.

I could be wrong, on this. I just can't see a business model that makes sense for replacing all "dumb" trailers with electrified trailers. It would be horribly expensive, the trailers would now require logistics, maintenance and support of their own and the transportation system isn't setup to support them.

To me it makes far more sense to keep trailers dumb and electrify tractors.

I'm assuming there are a lot more trailers than trucks in operation, so this seems less efficient than hybridizing the trucks themselves.

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.

(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.

Wouldn't the truck owner offer a discount for the fuel savings, or formulated differently add a fuel surcharge for loads that take more fuel to carry?

There by getting the trailer owner to care if they have loads hauled regularly.

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.

Alternators are suited to the electrical needs of the truck. Asking them for even another 1 KW is not practical.

Charging a hybrid truck's lithium batter at 1 KW is nowhere near enough power to be useful.

If you want to have the diesel engine charge the battery that means a total redesign if the truck, its engine, and its power train.

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.

[0] https://www.dat.com/blog/trailer-pools-friend-or-foe

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)

https://en.wikipedia.org/wiki/Road_train

Really elegant and beautiful design. The fact that this can be done as an add-on to the vehicle without having to touch any of its existing parts is impressive. It means that basically the truck doesn't have to be taken out of commission for an 'upgrade' and that makes the design highly practical (for anyone who has a business to run.) What a great idea.

I'd like to see the financials for this from a haulage operators perspective; payback period, return on investment etc

Also would be cool to see the sums if solar panels were added to the equation

Top surface area of a semi trailer is around 42 square meters, given a trailer width of 102" and length of 53'. It's typical to get around 250W per square meter from PV in ideal conditions, so that's 10.5kW. It takes about 15kW to push a Tesla down the highway at 60mph, so 10.5kW is not a negligible amount. (Pushing a semi down the highway at 60mph takes a lot more because it's much heavier and has a much larger frontal area.)

So this is definitely not enough to power the vehicle going down the road, but it is enough to add significantly to its range. Again, assuming the truck is driving down the road at high noon during the summer and there are no clouds.

PV doesn't work for cars because they don't have enough surface area, but it is a reasonable idea for a semi trailer.

Pepsi sites 1.7 kWh per mile on short distance delivery with the Tesla semi

That would mean a power use of around a 100kwh while driving 60 mph.

That would extend the range by about 10% that's less then I would have expected, but still could make sense depending on the standing time.

100kw, not 100kwh. But I take your meaning, and your factor of 6.7 for the amount of power/energy a semi uses vs a Tesla sounds reasonable.

Trailers are also often parked for a while so could be a viable recharge scenario for the trailer batteries.

It could also cover other energy uses on the trailer, such as refrigeration, ventilation or position reporting/telemetry.

Unless a rig spends significant time not moving in daylight, I suspect the tow cost and other inputs to a PV attached to the rig is above the ROI for power.

It might mean the cabin AC can run when its parked, and keep things humane. It might supplement a refrigerated intermodal and prevent engine run-on so be good for noise.

I doubt it would extend range much.

Happy to be proved wrong. E.g. the entire truck-top surface area with an integrated trailer might be enough to make sufficient KW to be worth doing.

Trailers certainly spend more time sitting around than the trucks do during loading/unloading times, so if you put the panels on the trailer you would improve the ROI, although I’m not an expert on trucking and don’t know how long trailers tend to sit idle.

I suspect adding PV panels would have another issue, however, which is they’re frequently stacked on top of one another in shipping yards, etc. PV paneled trailers would likely not be stackable, and therefore containers would need to be repackaged for storage or transport outside trucking (IE a container ship wouldn’t be able to just drop a container on to a truck to ferry it, it’d need to be reloaded).

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