Skip to main content

About this free course

Download this course

Share this free course

Can renewable energy sources power the world?
Can renewable energy sources power the world?

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

2.1 Units of energy and power

A host of different units are used to describe energy and power, which can seem a bit confusing. But the following Table 1, where we have listed and described some of the most frequently used units, should clarify the meaning of the various terms.

Table 1 Common units of energy and power
EnergyPower
NameDescriptionNameDescription
Joule (J)Main scientific unit of energyWatt (W)Main scientific unit of power – defined as 1 joule per second
Kilojoule (KJ)Equal to 1000 (103) joulesMilliwatt (mW)Equal to 1000th of a watt (10-3)
Megajoule (MJ)Equal to 1 million (106) joulesKilowatt (kW)Equal to 1000 (103) watts
Gigajoule (GJ)Equal to 1 billion (109) jouleMegawatt (MW)Equal to 1 million (106) watts
Exajoule (EJ)Equal to 1 quintillion (1018) joulesGigawatt (GW)Equal to 1 billion (109) watts
Kilowatt-hour (kWh)The amount of energy produced by a power of 1 Kilowatt (1 kW) in one hour
Megawatt-hour (MWh)The amount of energy produced by a power of 1 Megawatt (1 MW) in one hour
Gigawatt-hour (GWh)The amount of energy produced by a power of 1 Gigawatt (1 GW) in one hour

As you can see from Table 1, most of the terms are used to describe larger quantities of the basic units – joules or watts.