kW v kWh – what's the difference?

Image shows Zapman, Electric Universe mascot, questioning the difference between kW and kWh

When it comes to the EV language, acronyms reign supreme. While some have become ubiquitous (EV = electric vehicle), others need a little more explanation.

This could not be more true than two of the most common EV acronyms: kW and kWh. Despite both appearing on every charge point, map and app - what do they mean and what’s the difference?

Let’s get plugged in…

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kW and kWh - what do they mean?

  1. kW = kilowatt represents the rate of power (i.e. an EVs energy input and output). 1 kilowatt = 1000 watts.

  2. kWh = kilowatt hour represents the storage of energy (i.e. the capacity of an EV battery).

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Did you know that the 'watt' in kilowatt is named after Scottish inventor, James Watt? This was due to his contribution to industry efficiency. Today, most electrical devices are rated in watts.

So, what’s the difference?

As mentioned above, kW represents the rate of energy that either goes in or out, of an EV. 

You’ll have noticed from looking at specifications that EVs have a maximum DC charging capacity - this is the maximum rate of kW that a vehicle can charge at. The higher the capacity, the faster the charge. For example, the Polestar 2 has a maximum DC charging capacity of 150 kW, whereas the Volkswagen ID.3 has a DC charging capacity of 125 kW. This would mean that to charge from 20 - 80%, using a 50 kW charge point, would take the Polestar 2 40 minutes, but take the ID.3 60 minutes.

To learn more about different types of charging rates, check out our blog: EV connectors and speeds.

A good way to visualise kW is as a garden hosepipe. The wider the hosepipe, the more water can come out.

Zapman, Electric Universe mascot, is using a garden hose pipe, where small electric droplet appear instead of water

This brings us to kWh, which represents the storage of energy and how much charge an EV battery can hold.

For example, the Polestar 2 has a battery capacity of 78 kWh, while the Volkswagen ID.3 has a capacity of 55 kWh. So, where does the hour (‘h’) come into this? If we look at the Polestar 2 battery capacity of 78 kWh, this means the battery can deliver 1 kW of power for 78 hours, or 78 kW for 1 hour. Typically, the larger the battery capacity, the more range an EV will have. 

A good way to visualise kWh is as a watering can. The larger the watering can, the more water it can hold.

Zapman, Electric Universe mascot, is using a watering can, where small electric droplet appear instead of water

EV efficiency is also measured in Wh. Instead of the traditional ‘miles per gallon’ (MPG) for fuel cars, EVs are measured by Wh per mile. Much like MPG, lower numbers for Wh per mile means more efficiency. For example, the Polestar 2 uses 306 Wh/mi, whereas the ID.3 uses 275 Wh/mi.

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