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.
| Energy | Power | ||
|---|---|---|---|
| Name | Description | Name | Description |
| Joule (J) | Main scientific unit of energy | Watt (W) | Main scientific unit of power – defined as 1 joule per second |
| Kilojoule (KJ) | Equal to 1000 (103) joules | Milliwatt (mW) | Equal to 1000th of a watt (10-3) |
| Megajoule (MJ) | Equal to 1 million (106) joules | Kilowatt (kW) | Equal to 1000 (103) watts |
| Gigajoule (GJ) | Equal to 1 billion (109) joule | Megawatt (MW) | Equal to 1 million (106) watts |
| Exajoule (EJ) | Equal to 1 quintillion (1018) joules | Gigawatt (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.