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EV 'kW' figures explained

By David Bonnici, 11 Sep 2020 Car Advice

electric car

Whether you’re talking EV power, battery capacity or charging, everything seems to be measured in kilowatts. So how do they relate to each other?

Electric vehicles are, in many ways, simpler than conventionally powered cars in that they have far fewer moving parts or things that can go wrong.

However, anyone new to EVs would be forgiven a little confusion at all the numbers relating to their power, battery capacity and how long they take to charge, as their respective units of measurement all contain a reference to kilowatts (kW).

EV CAR CHARGER

So what do the numbers and letters mean and how do you tell them apart?

EV motor power (kW)

The car’s power is fairly straightforward and refers to the electric motor’s maximum output. This is measured in kilowatts (or 1000 watts) just like a normal internal combustion engine (ICE). The higher the kW figure, the more oomph you'll get at the expense of energy consumption.

MORE: Is it time to go electric?

As the following list shows the power ratings of EVs aren't too different when compared with similar sized and performing ICE vehicles.

  •          Nissan Leaf - 110kW
  •          Hyundai Kona Electric – 150kW
  •          Mercedes-Benz EQC - 300kW
  •          Porsche Taycan Turbo S – 560kW
  •          Tesla Model S Performance – 595kW

Battery capacity (kWh)

The total battery capacity of an EV is measured in kilowatt-hours (kWh or kW-h). This rating tells you how much electricity can be stored in the battery pack. It's a unit of energy just like calories and one kWh is equal to 3600 kilojoules (or 3.6 megajoules). Unlike kW it is not a unit of power.

Lower-powered EVs require a smaller capacity; for example the Nissan Leaf stores 40kWh and the Hyundai Kona Electric 64 kWh. The Porsche Taycan Turbo S meanwhile stores a maximum of 93.4 kWh.

 

If all these cars had the same electric motor (and thereby the same maximum amount of power drawn from the battery at any given time) the Porsche would have the longest range because of its higher capacity.

MORE: How much does it cost to charge an EV?

However, the Porsche has a 560kW motor that's designed for high performance and that comes at the cost of range, which is about 405km. But the Hyundai Kona Electric has a 557km range even though it has a smaller battery capacity because its motor is less powerful.

The reference to 'hours' in the unit is a source of confusion for some but it's fairly simple. The kilowatt unit is calculated as the amount of energy necessary to produce kilowatt of power sustained for one hour.

Charging point power (kW)

A kilowatt is also the unit of measurement and energy used for charging points. With electricity, a watt is simply the voltage (volts) multiplied by the current (amps), which means the higher the kW number the more electricity is being used to charge your car, which means quicker charging.

MORE: Here are the fastest charging electric vehicles

This is why a 400v/50kW rapid charger will charge an EV far quicker than a 240v/2.4kW socket in your garage.

READ NEXT: WhichCar EV Guide