kW and kWh: Understanding The Difference

The terms "kW" and "kWh" frequently appear when reading about electric vehicles, yet their distinction remains a mystery to many. Let's look into what sets these metrics apart and why they hold significance in the world of EVs.

Defining kW and kWh
To begin, let's unravel the acronyms: "kWh" stands for kilowatt-hours, while "kW" represents kilowatts. Despite their similar abbreviations, it's important to understand that these units are not directly comparable; they serve different purposes.

Understanding kW
Kilowatts (kW) means power – the rate at which energy is consumed or generated. Imagine an EV charger as a tap: kW measures the flow rate of electricity from the charger to the vehicle. Charging stations typically range from 3.7kW to 350kW, dictating how swiftly a battery can be replenished. The Onboard charger (OBC) of an EV will determine by how much the tap can be turned on. Can the tap be turned on fully to receive all of the current flow that a charger can distribute, or just partially to receive some of it? The answer to this depends on the capacity of the EV’s battery and will be different for AC (Alternative current) charging which every EV can accept and DC charging, which only some EV’s can accept. For more detailed information, you can read our article on EV charge capacity.

Understanding kWh:
Kilowatt-hours (kWh) corresponds to the total amount of energy an EV stores or consumes. It therefore indicates the capacity of an EV's battery. For example, the Nissan Leaf offers models with 39kWh and 59kWh batteries, affecting the vehicle's range between charges. To put it simply, kWh measures the capacity and endurance of the battery, akin to how litres measure a fuel tank's capacity. So, the higher the kWh, the further an EV will travel on a single charge.

Consider an 80kW electric motor paired with an 80kWh battery. If the motor ran continuously at its peak speed without using any other source of battery drain, the battery would be fully drained in precisely one hour.

In essence, while kW relates to the rate of energy flow (charging speed or motor power), kWh reflects the total energy capacity of the battery. Understanding this distinction allows EV users to make informed decisions about charging options and battery performance.

So, next time you encounter kW and kWh in the EV vocabulary, remember: one measures power, the other measures energy. Clear as day, right?