A kilowatt hour (kWh) is a measure of energy while a kilowatt (kW), or 1 000 watts, is a measure of power.
What is energy?
Energy is a measure of how much fuel is contained within something or used by something over a specific period. The kWh is a unit of energy.
What is power?
Power is the rate at which energy is generated or used. The kW is a unit of power.
What is a kilowatt hour?
A kWh is a measure of how much energy is used.
It is not the number of kW used per hour – it is the amount of energy used to keep a 1 000-watt appliance running for an hour.
A 100-watt light bulb would use 1 kWh in 10 hours.
A 2 000-watt appliance would use 1 kWh in half an hour.
A 50-watt item would use 1 kWh in 20 hours.
What is the difference between kWh and kW?
Think of kW as the speed you’re running at and kWh as how far you’ve run. A kWh is the amount of energy equivalent to a power of 1 kW running for 1 hour.
The analogy of two cars
Both cars go on a seven-hour drive.
Let’s say kilowatt (kW) = speed (km/h)
The one car’s speed ranges from 120 km/h to 190 km/h. If it were a building, it would be using between 120 kW and 190 kW at any given moment.
The other’s speed ranges from 80 km/h to 120 km/h. If it were a building, it would be using between 80 kW and 120 kW at any given moment.
The kW then measures the energy being used at a given moment, not over time.
Let’s say kilowatt hour (kWh) = distance travelled (km)
Even though both cars were driving for the same number of hours, the distance they covered was very different.
If you think of distance covered as usage (kWh), you can see how two buildings can operate for the same amount of time but use drastically different kWh.
The kWh is a measure of consumption or total energy used over a specific period.
The kW is a measure of demand or how much energy is used at a given moment.
Understanding the difference between kW and kWh will help you make the right decisions about renewable energy.
The most lasting and universal consequence of the French revolution is the metric system
– Eric Hobsbawm, Historian