## 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