Unit of measuring energy

What is a gigawatt hour ?

The gigawatt hour (GWh) is a unit for measuring energy. It is used to express the quantity of energy produced or consumed by a piece of equipment with power of one gigawatt for one hour.

Remember that the base unit for measuring a quantity of energy is the watt-hour (Wh). As a reference, 1 GWh equates to 1 billion watt-hours (Wh). This is also 1 million kilowatt-hours (kWh) or 1000 megawatt-hours (MWh).

Suffice to say it is a very substantial quantity of energy. That is why is it is usually used to indicate the quantity of energy produced in large power stations.

How many Joules in a GWh  ?

For information, the unit of measurement adopted in the international system to measure quantity of energy is not the Wh and its variations (kWh, MWh, GWh, etc) but the Joule (J). This unit of measurement is currently used very little in everyday language.

In this measurement system, 1 kWh equates to 3.6 million Joules. Therefore, 1 GWh corresponds to 3.6 x 10^12, that is to say 3.6 billion Joules !

The characteristics of the gigawatt hour

Be careful not to confuse gigawatt hours with gigawatts !

This is a common error when we talk about energy. Of course, the two units are closely linked. But their values can't be compared. A gigawatt-hour is used to measure quantity of energy. While a gigawatt expresses power, that is to say the energy flow produced or consumed at time t.

Let's take the example of a water jet for a better understanding.

The water flow measured when a tap is opened equates to power for electricity, expressed in GW.

The quantity of water that flows in an hour corresponds to the energy consumed during this same period: it will be measured in GWh.

How can an amount of energy be calculated in Wh, kWh, MWh or GWH ?

To obtain the quantity of energy consumed by an electrical appliance in a year, you need to multiply its power (in W, kW, MW or GW) by the number of hours of operation per day then the number of days of use.

For example, an electric radiator with power of 1 kW consumes around 1080 kWh per year if it is used for 6 hours per day for 6 months (that is to say 1 kW x 6 h x 180 days).

Examples and application

On household electricity and gas bills, suppliers always express the quantity of energy invoiced in kWh. Simply because this is the unit most suited to the levels consumed by households. According to the ADEME, on average French households consumed a little more than 4500 kWh of electricity per year in 2020.

However, the gigawatt hour is increasingly used as a unit of measurement for energy: notably in line with the production of batteries for electric vehicles. This unit of measurement is notably used to quantify the production capacities of gigafactories, the giant factories dedicated to producing large quantities of batteries for electric vehicles.

Some numbers expressed in gigawatt hours

  • Based on 4500 kWh of electricity consumed per year by a French household, 1 GWh approximately corresponds to the overall electricity consumption of 220 households each year.
  • In France, a data centre can consume up to 25 GWh of electricity each year.
  • According to a report published by the ADEME in 2013, the time change in 2009 allowed around 440 GWh of lighting to be saved per year. In France, this is the consumption required to light 800 000 households.
  • To equip its electric vehicles, in its Nevada gigafactory Tesla makes a number of batteries whose energy equates to 35 GWh per year. As a comparison, a country like Togo produces 90 GWh of electricity per year.
  • In France, overall electricity production in 2021 was 522.9 terrawatt hours (TWh), that is to say 522 900 GWh.

Regulatory framework

Not applicable