Going the Extra Mile - Breaking Down EV Efficiencies
As electric vehicles become more prevalent, understanding their performance metrics is crucial. In this article, Kush explores how the efficiencies of different EVs compare, what factors contribute to these efficiency ratings, and how we should interpret them.
Lucid Motors recently claimed that the 2025 Lucid Air Pure would be the world’s most efficient EV, achieving a record 5 miles/kWh with a 420 mile range from an 84kWh battery. CEO and CTO, Peter Rawlinson stated “This is a landmark achievement validated by the EPA”, and said that Lucid was setting its sights even higher, at 6 miles/kWh.
This got me thinking about EV efficiencies. I recently took delivery of an EV, and when looking at the various options out there, I was mainly focussed on things like performance, looks, tech, and range. I didn’t really pay much attention to the miles/kWh value, but looking back at it, maybe I should have. Miles per gallon (MPG) is a common efficiency metric for gasoline cars, and similarly, miles/kWh shows how costly it is to run an EV and how efficiently it uses energy—two key reasons for choosing an electric vehicle, right?
EPA Range Rating
The Environmental Protection Agency (EPA) has an official methodology for calculating the range of EVs, found here. Manufacturers test their own vehicles, usually pre-production prototypes, and report the results to the EPA. The EPA reviews the results and confirms about 15%–20% of them through their own tests at the National Vehicles and Fuel Emissions Laboratory.
The test methodology is as below:
Why use Miles/kWh?
Miles/kWh is a direct measure of how effectively each unit of battery capacity is being used. Note this may not be the only value that a manufacturer wants to optimize, they may want to put more emphasis on speed, luxury features or off road capability for example than the fuel efficiency.
Miles/kWh gives us a good idea of how efficiently the the car is designed and how well it utilizes the energy in the battery, including everything from:
Weight optimization in the battery pack and the rest of the vehicle
Motor and powertrain efficiency
Aerodynamics
People are already used to working with MPG and so this value should be relatively easy for consumers to understand.
We can use this value to calculate how much it will cost to operate the EV.
We of course want to maximize the Miles/kWh value while minimizing the $/kWh to reduce our $/mile as much as possible.
To maximize our Miles/kWh we can:
Choose an EV with a high Miles/kWh value (you can do this by looking up the MPG(e) value on the EPA’s website, which we’ll look at soon)..
Drive efficiently by:
Utilizing regenerative braking
Avoiding harsh braking and acceleration
Avoiding high speeds (aerodynamic drag increases with the square of the speed)
Avoiding excessive use of ancillaries such as AC and power hungry entertainment systems.
To minimize our $/kWh we can choose to charge at locations with low electricity costs, such as at home or charging stations with lower rates. Superchargers are faster, but tend to be more expensive.
Geotab did some interesting analysis on the effect of ambient temperature and speed on EV range by simulating a model of a sedan and delivery van based on real trip data.
They found that the optimal temperature for range is 68°F, but the speed at which the range is maximized changes. At lower and higher temperatures, more energy is needed to keep the cabin and driver at a comfortable temperature, reducing the range. At higher and lower temperatures, the speed for maximized range increases as it’s a tradeoff between higher speeds causing more drag but also reducing the trip time and therefore the amount of time the HVAC is running. The optimal speeds for the van are lower than the sedan due to the less aerodynamic shape of vans.
Charge Efficiency & Battery Round Trip Efficiency
The numbers above talk about efficiency when driving, similar to the discharge efficiency of a battery. But we also need to charge the battery in the car, and charging is not 100% efficient. This is another area where efficiency becomes important. Batteries usually have an RTE value, or round trip efficiency.
Li-ion cells typically have >90% RTE, varying depending on chemistry and brand. The <100% efficiency is caused by losses due to side reactions, internal resistances and degradation of electrode materials, which all get worse as the battery ages, leading to reduction in RTE with battery aging.
RTE affects the miles/kWh value in our price calculation from before. Remember the equation below to calculate miles/kWh?
An 84kWh battery with a 90% RTE value actually takes 93.3kWh of energy to fully charge (84/0.9). The lower the RTE, the more energy needed to charge, and the lower the miles/kWh value.
EV Comparison
The EPA keeps an official database of EV car range and efficiencies. The below chart compares the efficiency parameters of several EVs, ranging from small EVs to the (very) large. All models are 2024.
The snip below also provides the 10 most efficient 2024 models according to the EPA. As can be seen, Hyundai, Lucid, Tesla and Lexus lead the way in terms of efficiency. Rivian and Hummer are lower, which is to be expected as they are larger SUV/pickup style vehicles which are naturally heavier and less aerodynamic as they’re expected to carry larger loads and go off road.
What does this all mean?
With EV ranges increasing all the time, range anxiety is becoming less of a concern for buyers. In 2022 the average American only drove 30.1 miles a day and if you can charge your EV at home, suddenly range isn’t a big issue. As Lucid’s statement suggests, the emphasis should perhaps be placed on how efficient we can make EVs and how we can make best use of the energy stored in the battery. Part of the transition to clean energy is going to require us to make better use of the energy available, even if it’s from renewable sources.
The bottom line is that focusing on efficiency will make EVs cheaper to operate and if we want to encourage positive change, driving down the price will be the key.
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