How to calculate real-world range

Manufacturers publish a figure in their brochures known as the WLTP figure. The Worldwide Harmonised Light Vehicles Test Procedure that determines the range of a vehicle is conducted under pleasant temperatures of between 20 and 23 degrees and uses a combination of road settings (urban, interurban, motorway). (If you want to know more, you’ll find a detailed description in this blog post by Generation Strom.)

This skilfully devised procedure produces a very good guide figure for the vehicle. However, the electric car driver’s real-world experience may differ widely from these figures. We explain the four key reasons for this below.

1.    Speed, driving style and other spanners in the works

As with ICE vehicles, your driving style and the speed at which you’re travelling naturally play a significant role. If you’re a regular electric speed freak or spend more time on the motorway than in 30 km/h zones, your consumption is going to be much higher. This is because the electric motor has to use more power in order to accelerate, for example, or to overcome higher drag.

Similarly, winter tyres and wet or snowy conditions will also increase your average consumption. And – believe it or not – even a tyre pressure variation of just 0.2 bar will make a difference to the range indicator.

2.    Net vs. gross

Many manufacturers are more than generous with extras for their new cars but less so with information about the battery that’s fitted. It is often not clear at first glance whether the kWh battery capacity quoted is gross or net. This distinction is crucial, because the gross figure refers to the battery’s total capacity whereas in real-world operation only the net capacity is usable.

The difference between gross and net capacity is down to the battery management system (BMS), which monitors and manages the overall (gross) battery. This BMS regulates charging and discharging processes and ensures that the battery is never overcharged or totally flat. Completely draining the battery or charging it to the max would damage it, so lower and upper boundaries are set. Between the two is the usable net capacity, which should form the basis of any claims about the range.

3.    Degradation

Another reason for a lower range is something called degradation. Age, the number of charging cycles and the heat released when charging and discharging the battery all decrease the usable capacity over time. Degradation is slightly higher at the outset and then increasingly levels off. Measurements from Tesla drivers show that batteries lose capacity slightly quicker in the early days but even after 300,000 kilometres, still retain 90% of their original capacity. This means that most batteries should outlive their cars. It also effectively means that the advertised net capacity ceases to be available shortly after purchase.

4.    Temperature

Finally, the battery still needs a certain temperature window for the chemical processes to function at their best. With lithium-ion batteries, the optimal temperature is between 25 and 35 Celsius. When temperatures are lower, internal resistance increases as the battery consumes part of the energy for itself. Higher temperatures, on the other hand, can be hazardous to the battery’s chemical elements. So if you start with a cold battery, part of the energy will be used for battery temperature management and will no longer be available to power the vehicle. Warming the battery to the ideal operating and charging conditions can take a surprisingly long time – 200 kilometres of motorway or more, depending on the vehicle. Our Hyundai Kona fleet car has been known to take 300 kilometres of motorway driving to reach the ideal 25°C.

How to caculate real-world range Establish your actual consumption in winter and in summer, ideally over a fairly long period of time using your typical route profile. Subtract another five percent from the advertised net capacity to allow for degradation of the battery. Divide the usable battery capacity by your winter or summer consumption.

Calculation example Hyundai Kona Electric (2018)