Anyone who has read just a single article on this site will know that when towing with an EV you have to expect the normal driving range to be typically cut in half. I’ve previously discussed the need for more aerodynamic trailer/caravan designs to aid towing range. Well, there is also another approach to help reduce range loss which is emerging, self-propelled trailers/caravans. The concept has its pros and cons as I’ll discuss below.
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Introduction To Self-Propelled Trailers/Caravans
While EVs can tow trailers/caravans there is a significant hit to the range of the vehicle. As a general ‘rule’ any EV owner towing should expect the range to reduce by typically 50% of the car’s normal day to day range when not towing.
Up until this point, all trailers/caravans have been passive, in other words, their movement/propulsion has been completely dependent on the tow vehicle. What we are discussing in this article is the concept that the trailer/caravan is not passive, it has its own batteries and electric motors to power it.
The primary objective of this concept is to take load/resistance off the tow vehicle to increase range while towing. There are also additional benefits to this self-propelled trailer/caravan concept as I’ll discuss below.
However, there are also downsides to putting batteries/motors within the chassis of a trailer/caravan. So while I believe these types of self-propelled trailers/caravans will be a subsection of the market, I cannot see it being a significant proportion of the market until the distant future, if ever.
Before I discuss the pros and cons let’s first have a quick look at the two concepts that are showing the potential of self-propelled trailers/caravans. The first is the Dethleffs E.Home and the second is the Airstream eStream.
Dethleffs E.Home Self-Propelled Caravan
Dethleffs is a subsidiary brand of the Erwin Hymer group which is one of the world’s biggest leisure vehicle manufacturers. The E.Home project has been worked on since 2018. However, it was in 2021 when the project first demonstrated its results/capabilties.
The E.Home concept trailer was towed behind an Audi E-Tron 55 Sportback over the Alps mountain range. The trip was 240 miles without charging to demonstrate how the E.Home reduced the load on the E-Tron to provide an impressive real-world towing range.
If you check out my articles such as which electric tow cars have the longest range you will see the real-world range of the E-tron not towing is only typically around 230 miles. Therefore, towing a trailer 240 miles over the Alps shows the E.Home self-propelled caravan concept clearly works.
The E.Home caravan has a battery capacity of 80kWh and a motor for each wheel. The power output of each motor is 40HP continuously and up to 121HP max to each motor for a short period of time. The battery/motors added just under 600kg to the caravan. I would therefore estimate the total weight of the caravan to be just under 2,000 kg.
Airstream eStream Self-Propelled Caravan
The second concept of a self-propelled caravan has come from Airstream, called the eStream. However, the eStream is based on the same chassis, batteries and electric motors used in the E.Home above. The parent company of Airstream is Thor Industries which purchased the Erwin Hymer group in 2018.
The eStream is essentially a more premium/luxury version of the E.Home concept from Dethleffs. As a result, the eStream is heavier with a weight of around 2,500 kg.
The eStream is yet to go through technical testing on the road. One would expect that due to the additional weight of the eStream over the E.Home concept the range would be less. However, it will be interesting to see if that’s actually the case.
In my article on aerodynamic drag, I provide an example of a where a Tesla Model X owner found towing an Airstream caravan resulted in better range due to its more aerodynamic profile. Therefore, I’m very interested in what the on-the-road tests will show about the eStream.
Pros of Self-Propelled Trailers/Caravans
Ok, so the first benefit of a self-propelled trailer/caravan is obviously the additional range while towing. As I discuss in my article on Charging While Towing – The Biggest Challenge getting charge back into an electric car towing while on route is currently a significant challenge.
Hence, being able to go further while towing and potentially avoiding the need to rapid charge is a clear benefit. Then again, by the time you can actually purchase a self-propelled trailer/caravan I would certainly hope there will be a pretty extensive network of dedicated rapid chargers suitable for tow vehicles.
But that aside, more range while towing is obviously a positive, but what are the other associated benefits of putting batteries and motors within the chassis of a trailer/caravan?
Improved Towing Stability/Safety Features
The ability of the trailer/caravan to provide power independently to each wheel means that a new generation of towing stability features/software could come about to make it the most stable/safe towing experience to date.
Anyone who has experienced sway, pitching or snaking while towing knows its not a pleasant experience and in some situations it can lead to tragic consequences. Add in the regenerative braking not only of the car but of the trailer and it means stopping distances could be further reduced.
Additional Traction For Sticky/Slippy Situations
While adding 600kg to the weight of the trailer/caravan means getting stuck on softer surfaces is more likely, the fact that the trailer/caravan is self-propelled would help in certain situations.
Now, how much it would help would obviously depend on the type of tyres fitted and the traction they provide. A balance would have to be struck with the tyre choice between low rolling resistance to aid range and traction/braking distances in sticky/slippy situations.
As a caravan site owner (Horton Common) many of our guests have motor movers fitted to their caravan to move it around once unhitched from their car. However, a proper self-propelled caravan would take that manoeuvrability to the next level.
Off-Grid and V2H/V2G Capabilities
Let’s presume for the second the caravan arrives at its location with a decent amount of charge left in its battery. That therefore obviously opens up the possibility of some pretty comfortable off-grid camping with pretty much all services available, maybe even heating without the need for gas.
However, let’s say when not in use the caravan is parked next to your house. Well, that’s where V2H (Vehicle 2 Home) and V2G (Vehicle 2 Grid) possibilities come into play. This could mean powering your home during a blackout or even making you money by charging with off-peak electricity and selling that energy back to the grid at a higher price.
Cons of Self-Propelled Trailers/Caravans
Right, so as I’ve discussed above, there are clearly benefits to the concept of a self-propelled trailer/caravan but there are also some downsides, the first obvious one is cost.
Battery costs while they have reduced significantly over the last decade still are attributable to the higher cost of EVs over internal combustion vehicles of a similar size. Hence, until battery costs reduce considerable, adding a large battery pack into a trailer/caravan is going to increase their cost considerably also.
Which is I think why Airstream/Dethleffs during their concept projects have alluded more to a rent/hire scenario for these self-propelled trailers. However, as a small caravan site owner most caravan owners I know want to own their own caravan, not rent/lease it.
The Additional Weight/Higher Towing Capacity Needed
The key purpose of adding batteries/motors to the trailer/caravan is to take load off the tow vehicle to increase its range while towing. However, the tow vehicle will still need to be capable enough to tow the trailer/caravan with an empty battery.
Therefore, a larger/more capable tow vehicle will be needed to legally tow a heavy self-propelled trailer/caravan. So not only is the self-propelled trailer/caravan more expensive to buy in the first place a heavier/more expensive tow car will be needed to legally tow it.
Granted, as battery technology progresses (solid-state etc) the weight of battery packs will likely reduce (at least I hope so). However, currently and I would imagine for the next decade, batteries are going to continue to add significant weight to vehicles.
Towing a Trailer/Caravan With An Empty Battery
So this issue is carried over from my point above, but it is a separate scenario. If the battery was to deplete while still towing, the assistance it provided to propel the trailer/caravan has then become a hindrance once empty.
The electric tow cars range will then reduce faster than if it was just towing a ‘normal’ passive trailer/caravan of the same size due to the additional weight of the battery/electric motors.
Additional Charging Bay Requirements
For this concept of a self-propelled caravan to work it also needs to be charged along with the tow vehicle. Airstream in their presentation above discusses how the eStream can be unhitched and it can self-propel itself over to a charging bay. They also described how its size is suitable to fit inside a standard charging bay.
Well, the same would obviously not be true of a larger caravan and the caravan can only self-propel provided there is power left in the battery. If the battery is empty getting the caravan to a charging bay is obviously going to be a big problem based on the layouts of current rapid charging infrastructure.
What it also means is you would need two charging bays to be available when you stopped, one for the car and one for the caravan. You could charge one after the other at the same stall, but you would be charging for a very, very long time.
My Thoughts On Self-Propelled Trailers/Caravans For EVs…
There is undeniably a ‘range problem’ with the current generation of EVs when it comes to towing. As such, I can see the merits of a self-propelled trailer/caravan to take load off the EV to increase its range when towing.
While the concept has a series of benefits it also has notable drawbacks/limitations. The additional cost which would be added to the trailer/caravan is obviously clear. Though as I’ve discussed above, that’s not the only drawback.
Personally, I think a better approach is to focus on reducing the weight of trailers/caravans where possible, but even more so, to improve their aerodynamic profile as much as possible. Continuing those weight/aero improvements with EVs to boost their efficiency, along with improvements in battery technology.
Ultimately though, the solution to the ‘towing problem’ with EV is to make rapid charging infrastructure not only more ubiquitous but to make rapid charging stations much more friendly to EVs towing with better access, pull through charging stalls etc.