It’s the trailer, stupid!...

[jr4488]

When I have 35,000 pounds in the trailer:

-my engine produces 570 hp going up a grade and gets 1.8 mpg

-my engine produces 87 hp on flat pavement going 65 mph and gets 7.4 mpg

-my engine produces 40 hp on a downhill grade and gets 13.5 mpg

- my engine engages the “Jake brake” on a steep downhill grade and produces negative hp

I’ve got 160 square feet of space under my trailer to mount batteries.

I’ve got 8,000 pounds of available gross weigh for batteries.

I’ve got 425 square feet on the roof for solar panels.

Based on my graph of mpg vs hp vs speed, a 20 hp push from the trailer would buy me an extra 2.9 mpg at 65 mph.

For all you engineers out there, how long could an 8,000 pound battery pack produce 20 hp on a motorized trailer?

This trailer configuration could turn a diesel tractor into a hybrid or extend the range of the Tesla semi. Plus, you could retrofit existing trailers.

What do you think?...

Jack

 

[3s-a-charm]

...and how much impact would towing the additional 8,000 lbs be on your range. This is similar to when people were considering towing a trailer full of batteries in their Model S/X to increase range but I believe in most cases the disadvantages would outweigh the benefits...

 

[jr4488]

...and how much impact would towing the additional 8,000 lbs be on your range.

I know a 40,000 pound load will get me 7.2 mpg.

I know a 35,000 pound load will get me 7.4 mpg.

I know a 20,000 pound load will get me 8.2 mpg...

Jack

 

[DarthPierce]

Well, 20 hp is about 15kW. By an 8000lb battery, I assume you mean there's 8000lbs available for motors, inverters, chargers, gearboxes, and batteries... so let's say 7000lbs for batteries alone That's 3180kg. I believe currently we're looking at 170Wh/kg so that's 540kWh.
540kWh/15kW = 36 hours.

I'd imagine you'd want to get more power than just 20hp for less time than 36 hours, say ~90hp for 8 hours? Then again, there's ton's of stability issues with the trailer pushing - it's like balancing a broomstick upside down on your hand.... So you'd probably want to put that power in the tractor instead. Oh - that's what Tesla did ;-)

Edit to add:

You didn't actually ask anything about the solar part but mentioned it in passing - 425sqft is about 40m^2.

This will be flat on the top, and not in any way able to track the sun.
The following is extremely contingent upon latitude, weather, and shading from trees/buildings, but for a super quick number, I'm grabbing insolation numbers for Goodland, Kansas since it's really close to the geometric center of the country and isn't especially desert-y or grey (like Phoenix or Seattle) and there's data from NREL for it (https://www.nrel.gov/docs/legosti/old/5607.pdf).

That gives an annual average of 4.7kWh/day/m^2, that's the actual energy hitting the surface, the PV panel then must convert that to electricity, at let's say 17% efficiency. That means your container is now contributing about 32kWH/day.

Not too bad, that means you've got another ~6% or so of that 540kWh battery charge for "free"

 

[SageBrush]

There are a few minutes every day when the sun is right over your panels.
You can probably figure around 5 hours a day of equivalent sunshine.
If a panel converts 1/6th of the sun energy into electricity, then
Each square meter of panel collects about 0.8 kWh a day

Edit: I see that DarthPierce beat me to it.

 

[Farmertom]

It's something I've pondering as well up here we pull anywhere from 80,000lb to 136.000lb (across Canada per ARTAC specs and into the US). Some of the conditions we run in could really benefit from the added traction and controlled braking. Truck tractors could be setup with nominal power, say 300hp or so, something that could give the tractor the best weight advantage. The trailers it pulls could subsidize the tractor unit as per the capacity of the trailer or trailers, it could work on a similar principal as booster engines in a train.

Some of it will be cost vs gain, what's a battery pack like that going to be worth? Plus motors, inverters, controls etc.

Control wise it should be fairly easy to tie into an electronically controlled engine.

You could recharge the batteries on downhill grades. If the panels are integrated as part of the roof and even walls you gain some charging with very little input and weight added to the unit,.

I think final drives for Tesla's truck are fairly inefficient, they should develop a motor that surrounds the axle and drives the hub through a planetary gearset. It would require a complete redesign of the axle assemblies and foundation brakes. I imagine the R & D and time is far beyond what Elon is willing to put into these units at this time.

Sorry for rambling, it's an interesting subject

 

[mongo]

I think final drives for Tesla's truck are fairly inefficient, they should develop a motor that surrounds the axle and drives the hub through a planetary gearset. It would require a complete redesign of the axle assemblies and foundation brakes. I imagine the R & D and time is far beyond what Elon is willing to put into these units at this time.

From the video Tesla posted, the rear motors look to have one or two stages of gear reduction and direct mount to the rear axle. Motor assembly likely has captive final bull gear with internal spline the axle is mated with. Sort of like back to back differential carriers.

 

[Uncle Paul]

Maybe someone needs to design a Hybrid trailer for 18 wheelers.

The truck would have a normal diesel motor, while the trailer would have it's own batteries and electric motors on the wheel hubs.

You could use the electric powered trailer to add power to the truck, to mitigate the weight of the trailer.

A little far fetched, but might have some applications.

Not sure if a traditional 5th wheel hitch is designed to handle forward thrust.

 

[WannabeOwner]

If the panels are integrated as part of the roof and even walls you gain some charging with very little input and weight added to the unit,.

Personally I'm not seeing this ... PV panels are going to get dirty / knocked about / not be in sunshine enough hours of the day / at best angle. But there again I'm seeing new products starting to appear - e.g. PV film that can just be stuck onto an existing roof / surface, so a material like that would open opportunity (compared to current panels)

Pity that Tractor hasn't been designed with replaceable batteries. That would let you have two batteries, one at base being charged off static PV panels, at best angle, covering scrub ground / roof tops, and then just swap the batteries over ready for "tomorrow".

 

[Farmertom]

Personally I'm not seeing this ... PV panels are going to get dirty / knocked about / not be in sunshine enough hours of the day / at best angle. But there again I'm seeing new products starting to appear - e.g. PV film that can just be stuck onto an existing roof / surface, so a material like that would open opportunity (compared to current panels)

Your completely correct, it's only real benefit would be if it added only a small nominal cost to the unit new without adding any real cost to weight and maintenance and you were buying all the power to recharge this unit.

Pity that Tractor hasn't been designed with replaceable batteries. That would let you have two batteries, one at base being charged off static PV panels, at best angle, covering scrub ground / roof tops, and then just swap the batteries over ready for "tomorrow".

If you're not running the unit around the clock it shouldn't be an issue as you can recharge from any storage device you have at home base. How long does it take to charge from around ten percent to full charge?

 

[Farmertom]

Maybe someone needs to design a Hybrid trailer for 18 wheelers.

The truck would have a normal diesel motor, while the trailer would have it's own batteries and electric motors on the wheel hubs.

You could use the electric powered trailer to add power to the truck, to mitigate the weight of the trailer.

A little far fetched, but might have some applications.

Not sure if a traditional 5th wheel hitch is designed to handle forward thrust.

We've discussed it a bit, probably the biggest issue would be developing and building a whole new fleet of trailers that may not mix with existing technology, could be pretty expensive.

Existing fifth wheels would handle forward thrust easily.

 

[WannabeOwner]

If you're not running the unit around the clock it shouldn't be an issue as you can recharge from any storage device you have at home base

Pity to have to have a static battery at home base, to store your daytime-PV electricity, and then discharge that to charge the truck battery ... charging a "spare" truck battery would have less waste (although its not a huge amount ...) and fewer batterycycles plus no waiting time to recharge, just swap over.

Anyway, that pipedream is dead! as Tesla haven't done it that way about. So you'd have to buy PowerWall if you want to store your own PV electricity (or you have Time-of-Use charges which you can time-shift, although maybe for overnight charging your rates are cheap? - that will change with time as more Solar is installed and the excess becomes available in the daytime ...

How long does it take to charge from around ten percent to full charge?

All Tesla cars charge (i.e. irrespective of battery size) from 10% to 70% in about 30 minutes (at Supercharger), so I presume if enough power is available, and with suitable charger, a truck battery will also charge 10% - 70% in 30 minutes. Elon implied as much in his presentation. From 70% to 80% is a bit slower, a lot slower from 80% o 90%, and 90% to 100% does not benefit from supercharger and takes around an hour - i.e. about the same speed as I get on my home charger.

Beefy charging equipment is expensive, so I'll be interested to see how that plays out for small operators [who want to install home-charging].

 

[LMichel]

Couldn't having one of those trailers also decrease (maybe eliminate) the use of Jake Brakes on a diesel?
Imagine a trailer with motors, batteries, a wireless device mounted up in the cab that was designed primarily to boost HP when hill climbing and taking load when descending. Interesting prospect. Pretty sure the power and air could work exactly the same way and be isolated from the "EV" part. Such a trailer could be a product of its own!

 

[mongo]

Couldn't having one of those trailers also decrease (maybe eliminate) the use of Jake Brakes on a diesel?
Imagine a trailer with motors, batteries, a wireless device mounted up in the cab that was designed primarily to boost HP when hill climbing and taking load when descending. Interesting prospect. Pretty sure the power and air could work exactly the same way and be isolated from the "EV" part. Such a trailer could be a product of its own!

That has been looked into with a purely mechanical system (compressed nitrogen/ hydraulic accumulator) for stop and go situations.

 

[Big Earl]

Tractors have much higher utilization than trailers. You’re better off investing the money electrifying the tractors than the trailers.

Reefer trailers are a different animal and should be electrified whenever possible.

 

[jerry33]

1. The additional weight of the solar panels is just where you don't want it--on the roof. Not great for stability.

2. This only works for fleets that have their own trailers and don't pull anything else. This eliminates a lot of potential sales.

3. From a 10 km view, there are two kinds of trucks: Those that max out on weight and those that max out on volume. The majority are the maxed out on weight variety. Every kg that is part of the truck means less revenue per trip. So you have the dubious benefits of solar panels on a truck against loss of revenue that's easy to calculate. (Assumes current technology--when solar panels are 2mm thick, have elements that rotate to face the sun, weigh 5 kg or less per panel, and are 70+% efficient, then there is a strong case for them on trucks.)

4. One of the advantages that subways with tires have over subways with steel wheels is that they require only one motorized carriage per car rather than two. This saves in original cost, weight, and energy used. My guess is that you would probably gain more with large singles than with solar panels. Large singles have far less rolling resistance than duals (speed gain of 2 - 4 mph), weigh significantly less, and allow a wider track for increased stability (assumes the truck/trailer is designed to use them).