That a tank full of fuel will empty your wallet is common knowledge here in India. Also common knowledge is the fact that a regular internal combustion engine (ICE) car will give you better fuel economy on the highway than in the city. However, this isn’t the case with EVs; in fact, it’s the opposite. Why is that so?
Inertia
An internal combustion engine is at its peak efficiency only when running in a particular RPM band and under low load conditions. On the highway, where the car and engine are cruising at a steady pace, it’s almost always in this efficient state and thus uses very little fuel.
Having to constantly accelerate and decelerate in the city traffic, meanwhile, takes a toll on a car’s mileage, as fighting inertia during acceleration uses up a lot of fuel. This is also the case in an EV, which will use more energy while accelerating.
However, it’s during the deceleration phase that a key difference between an EV and an ICE vehicle arises. When a driver releases the throttle pedal in an ICE vehicle, it uses no fuel, but in an EV, not only does it not use any energy, it actually generates some in a process known as regeneration.
Regen
By its construction, an electric motor can be reversed to function as a generator. So when an EV is slowing down – while coasting or even braking – the motor switches over to generator duty and uses the vehicle’s momentum (kinetic energy) to generate energy that is fed back to the battery (regeneration).
This, essentially, is why an EV offers a higher driving range in the city. Unlike on the highway, where there is constant throttle input, the start-stop pattern in the city regenerates energy thus increasing the car’s driving range.
Also good to know
The level of regeneration can be set by a manufacturer, and some even allow a selectable level on the fly, where a higher setting feeds more of the car’s momentum into the generator resulting in a stronger braking feel, or a lower setting that generates less energy but allows the car to roll more freely.
It is also important to note that while the process of converting kinetic energy from a car’s momentum to electrical energy in the battery is quite efficient, it does not equal to the amount of energy that is expended in moving the car forward in the first place. Thus, regeneration can only top up energy and cannot magically create an endless supply.
Gears
Another smaller factor is the gearbox. EVs do not really need one as an electric motor develops its maximum torque from literally a standstill and it stays pretty consistent across the rev range. Thus, they only employ one ratio that is a balance between city and highway driving. An additional gear could help improve range, but for now, most EVs simply forego the additional cost and weight, and opt instead for a single speed.
