This is an attempt at creating a model to calculate the consumption for an electric car while driving at constant speed on a horizontal surface and with no head- or tail wind.

The main purpose is to get a feeling for what and how much the consumption is affected by speed, temperature, height, rolling resistance aso.

It is probably too optimistic to expect to be able to get consumption numbers that is very close to real world measurements.

When the car is being driven at a constant speed without having to break for lights and other traffic, it's consumption is a sum of 5 different parts - 7 if you have the heater or AC running and is driving up an incline

The parameters that matters most between models of cars is: Weight of car, Drag coefficient, Tyre rolling resistance coefficient and Drag reference area. I have entered the numbers for a Hyundai Kona Electric. If you want to experiment with numbers for another model, you can find the fields in the table below this section to enter them in.

Parts of the total consumption

1. The wind drag is affected by speed and altitude - and to a far lesser degree of humidity (around a few promilles).
2. The tyre drag is just affected by the rolling resistance coefficient of the tyre. Not currently part of the model for this site is the effect of speed on the rolling resistance. It is not much up to about 90-100 km/h, but then it climbs about 40% until 180 km/h.
3. The transmission loss is specific to the individual transmission system of getting rotations from the engine to the wheel. To simplify it is set to 3%
4. The motor efficiency is specific to the individual model of motor, so on this site it is approximated as a smooth parabolic curve between 85% and 96%, with 90 km/h as the speed with the best efficiency, and then trailing off to 85% with speeds going either down towards 0 km/h or op to 180 km/h.
5. The DC to AC inverter is converting the direct current from the batery to the alternating current that the motor needs. The efficiency of the converter is set to 95%
6. The battery discharge efficiency is due to heat loss from the chemical reaction in the battery when it is being used. It is set to 90%
7. The heater or air conditioning will of course also contribute to the amount of electric energy used per km you drive. So in that sense you use more energy for heating per kilometer the slower you drive.
8. When driving up a hill the car is receiving potential energy from the battery. This energy can be recouperated (with some loss) when driving down the hill again by making the motor having to use less power to move the car forward - or even be converted beck into chemical energy in the battery again by using the "regen" feature of the car, where the motor is used as a generator creating electriciy that is then used to charge the battery.

The estimated consumption depends on some values that I have tried to guess a sensible value for. They are the tyre rolling coefficient, motor efficiency, DC to AC efficiency and battery discharge efficiency.

The motor has differen efficiency at various rpms and load, so I was inspired by a full plot of this of the motor in the Nissan Leaf to make the model described in the list above. The leaf motor efficiency diagram can be found here at page 11.

Please write in the forum if you have suggestions for a better model or values - or other feedback.