Guide To Electric Tow Car Efficiency (Wh/Mile) & (Miles/kWh)


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Electric cars are very efficient compared to internal combustion engine (ICE) cars in terms of using their onboard energy to produce movement. However, this article is not about the general benefits of electric tow cars compared to ICE cars. This article will discuss how efficient an electric car is when its towing and how to compare one electric car to another. After all, a more efficient electric tow car means more towing range. Therefore, you will want to understand what are good/bad efficiency figures for electric cars.

Electric Car Efficiency
The efficiency of an electric car will fluctuate depending on how the car is being driven and what its doing, for instance towing will negatively impact efficiency: Image – Teslamotorsclub.com

Purchasing a more efficient electric tow car will obviously save money on charging costs. However, particularly for towing, the most significant benefit with better efficiency is the additional range before you have to use a rapid charger or destination charger. Now, when it comes to towing, how efficient the electric tow car is itself is only part of the equation. Aerodynamic drag of the trailer/caravan also plays a significant role in how efficient the electric tow car will be over the journey.

Introduction To Electric Car Efficiency Figures

When previously purchasing a petrol/diesel car everyone will be familiar with looking at the quoted MPG (Miles Per Gallon) figure to determine how efficient the car is. Well, with electric cars the to two main means to compare/measure efficiency is either Wh/Mile (Watt-hours per mile) or Miles/kWh (Miles per kilowatt-hour). Now, in the US they also use MPGe (Miles per Gallon Equivalent) to state the efficiency of electric cars. However, that’s not an efficiency measurement used in the UK (yet).

A Watt is a measurement of electricity consumption you will be familiar with as that figure is on the back of your low power home electrical devices such as lights/phone chargers. Now, higher powered devices (kettles etc) will state kW (kilowatt), with a kilowatt simply being a thousand watts. Hence, 1kW is simply 1,000 Watts of electricity. Now a Watt/Kilowatt is a measure of power, and a Watt-Hour/Kilowatt-Hour is a measurement of energy. In this instance, as we are discussing efficiency over the distance of a mile, we are concerned with the measurement of energy, hence Watt-Hours/Kilowatt-Hours.

Wh/Mile VS Miles/kWh

Some electric cars (Teslas for example) display their efficiency/energy consumption as Wh/Mile (Wh/Mi is the proper abbreviation) other electric cars use Miles/kWh. This can be confusing when comparing and discussing the efficiency of electric cars against one another. As with Wh/Mile, a lower figure means higher efficiency and for Miles/kWh a higher figure means higher efficiency. To explain this difference and how to compare/convert the two measurements as simply as possible please check out the video below from EVM.

A very quick and easy guide to electric car efficiency figures/conversions

As is stated in the video above with MPG figures higher is better/more efficient. Therefore, most people will likely feel more comfortable with Miles/kWh efficiency figures. Currently, Tesla prefers to display Wh/Mile figures in the Model 3, Y and X as can be seen in the image at the top of this post, and don’t offer an option to display Miles/kWh efficiency figures. Though that could change in the future with a software update.

What About Towing Efficiency Figures?

In the video above, some typical efficiency figures are provided as examples of bad (400 Wh/Mile), Ok (267 Wh/Mile) and good (200 Wh/Mile). Those figures are a good representation of where current electric car technology stands in terms of efficiency. However, those figures are not representative of an electric car when towing. As I discuss in my article on can electric cars tow, you should expect roughly a 50% range reduction while towing. Hence, the efficiency figures are half as good/double the energy consumption. Therefore, for the same examples when towing it would translate as bad (800 Wh/Mile), Ok (534 Wh/Mile) and good (400 Wh/Mile).

Elevation Changes & Regenerative Braking

As you may very well be aware, to varying degrees depending on the specific electric car regenerative braking can actually put energy back into the battery pack. Hence, this is one of the reasons electric cars are more efficient than ICE vehicles. For instance, in the image at the top of this article, you can see a green section on the Tesla Consumption graph where the efficiency is actually in minus watt-hours per mile. Hence regenerative braking is taking place at that point.

Therefore, if you are towing downhill the efficiency figures will look great, you may even gain range! However, once you have to start towing uphill average consumption/efficiency figures go out the window. When towing uphill you are not looking at a range reduction of 50%, it could be a far more significant reduction in range.

Efficiency Figures Help To Produce Predicted Range Figures

If you get into any electric car and turn the heating/AC on/off you can watch the predicted range figure go up and down. The electric car is factoring in the increased energy consumption of running the heating/AC to predict the available range. Many electric cars will also produce a predicted range figure based on energy consumption over the previous 5, 10, 30 miles etc. Hence, if you have been driving at high speeds down the motorway, the energy consumption will have been high (low efficiency) resulting in a lower predicted range than travelling at slower speeds.

This is where towing with an electric car can be a bit ‘tricky’. As of writing this article no electric car even once it knows a trailer/caravan is attached will provide a reasonably accurate towing range. Why? Well, once a trailer/caravan is attached the efficiency of the electric car will roughly be cut in half, hence potentially double the energy consumption. Therefore, at the start of the journey, the electric car may predict a range roughly double that which is actually possible with the trailer/caravan on the back.

Trip Computer Improvements Are Needed For Accurate Towing Ranges

Many electric cars come with a smart screen interface and SatNav/Trip Planner. To predict the most accurate towing range/efficiency figures the electric car is going to have to factor in lots of variables such as the terrain/elevation, temperature, wind speed/direction, size/weight and shape of the trailer/caravan. As of writing this article, no electric tow car has a trip computer which factors in all of those variables. Hence, this is where improvements are needed and can be made to provide accurate towing range/efficiency predictions.

Even Tesla who currently have the most advanced Trip Planner do not provide realistic/accurate towing range/efficiency calculations (yet).

While Tesla with their current Trip Planner do not factor in enough information to produce a realistic towing range I do expect them to be the first to market with a solution. All Tesla vehicles receive over-the-air software updates. Therefore, I expect an updated Trip Planning for towing journeys to be available at some point. I actually think its really important to own an electric tow car which can benefit from over the air updates, whether from Tesla or another manufacturer. In the coming years, I’m sure I’ll be writing an article about who is producing the best/most accurate trip planner for an electric tow car.

Electric Tow Car Efficiency Real-World Example

One of the best real-world examples I currently know of discussing electric car efficiencies when towing is from the YouTube channel The Bearded Tesla Guy. Using a Tesla Model Y he tows a caravan rated up to the maximum towing capacity of the vehicle in the US (3,500 lbs).

Now, as I’ve stated many times on this site, a general rule to electric car towing is a 50% range reduction, hence double the energy consumption/half the usual efficiency. The efficiency of a Tesla Model Y under normal driving conditions is around 275 Wh per mile. Doubling the energy consumption for towing would be around 550 Wh per mile.

Well, as can be seen in the video below, towing a load close to the cars maximum capacity which isn’t very aerodynamic and at high speeds (70 mph) the energy consumption can be higher, potentially much higher. As you can see below, under those circumstances, efficiency/energy consumption could be close to 1,000 Wh per mile!

A good real-world case study on the efficiency of an EV while towing

Speed Kills Efficiency

Part of the reason the video above is such a good example to reference about efficiency and towing with an EV is the reference to speed. At the 19.20 mark in the video above the topic of speed while towing is discussed. At 70 mph, the average consumption/efficiency was 938 Wh/mile, that’s very high indeed. At that speed/efficiency while towing the Model Y would have a range of just under 76 miles!

However, with just a 5 mph reduction in speed (down to 65 mph) the average consumption was around 700 Wh/mile. Therefore, towing at 65 mph would increase the towing range up to just under 103 miles. Just over a 34% range increase by dropping the towing speed by 5 mph! Further reductions in speed would also increase towing range but to a lesser degree. I discuss this more in my article on aerodynamic drag.

Best To Worst Electric Tow Cars For Efficiency

Below I’ve listed the average efficiency results for a range of cars from my electric tow car list. The efficiency figures come from the EV-Database.uk. Please note, the average efficiency figures below are when the cars are not being used for towing. Hence, when towing as discussed with the example above the efficiency/energy consumption figures could be twice that listed below. If towing uphill/high speeds with a very heavy/non-aerodynamic load, the energy consumption per mile could be considerably higher.

Electric Tow CarEfficiency (Not Towing)
Tesla Model 3250 Wh/mile
Tesla Model Y275 Wh/mile
Polestar 2305 Wh/mile
VW ID.4310 Wh/mile
Skoda Enyaq320 Wh/mile
BMW iX3325 Wh/mile
Tesla Model X325 Wh/mile
Nissan Ariya330 Wh/mile
Mustang Mach E330 Wh/mile
Mercedes EQC345 Wh/mile
Volvo XC40 Recharge365 Wh/mile
Jaguar I-Pace375 Wh/mile
Audi E-Tron380 Wh/mile

As you can see above, Tesla currently produces some of the most efficient electric tow cars with the Jaguar I-Pace and Audi E-Tron being the most hungry for electrons. Now while efficiency is an important consideration when choosing an electric tow car, other factors such as towing capacity, overall range and how fast the electric tow cars can charge are likely more important considerations. However, a more efficient electric tow car will give you more range for a set amount of energy, for since our 18kWh example above.

But What Makes One Electric Car More Efficient Than Another?

In future articles, I’ll get a bit nerdier and start to discuss what makes some EVs more efficient than others. Now you may rightly state a lighter EV will be more efficient than a heavier vehicle. This is true, however weight differences cannot fully explain the MPGe figures above. For instance, the Audi E-Tron is only slightly heavier than a Tesla Mode X. However, the Model X is much more efficient, so what gives? Well, its a combination of more efficient hardware and software, more on that to come.

Chris

Hi, I’m Chris. I own and write all the content on ElectricTowCars.co.uk. The content above is purely my own personal thoughts/opinions/research and should not be treated as professional advice. I hope you find the content above useful to help you find your future ideal electric tow car or truck.

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