At a steady load of 100 megawatts, a data centre would use 2,400 megawatt-hours of electricity in 24 hours. That is a worked example, not a measured facility: multiply power by time to obtain energy. The distinction helps readers compare a proposed data centre with a battery project, even when both announcements put a large number beside “capacity”.
| What you need to know |
|---|
| MW measures power; MWh measures energy over a period of time. |
| A steady 1 MW load uses 1 MWh in one hour. |
| The IEA illustrates a 1 MW, 4 MWh battery with four hours at full output. |
| A maximum power rating alone cannot establish actual annual electricity use. |
The US Energy Information Administration’s explanation of electricity units sets out the scale: one kilowatt is 1,000 watts, and one megawatt is 1,000 kilowatts. Its kilowatt-hour definition adds the missing time dimension. A kilowatt maintained for an hour corresponds to one kilowatt-hour. The same relationship applies at megawatt scale.
In the example above, 100 MW is assumed to be the actual load throughout the day. If the average load were instead 50 MW, the daily total would be 1,200 MWh. A maximum rating of 100 MW would remain compatible with either scenario; it does not tell us which load occurred.
A battery needs two numbers
The International Energy Agency’s glossary gives a storage example with 1 MW of power and 4 MWh of energy capacity. At full output, that corresponds to four hours. The MW figure describes the output rate; the MWh figure describes the amount of energy the system can hold.
Two hypothetical batteries could each hold 4 MWh while having different output ratings. At a constant 1 MW, that energy corresponds to four hours; at 2 MW, it corresponds to two hours. The second calculation only describes a battery capable of delivering 2 MW. It cannot be imposed on a device rated for a maximum of 1 MW.
These are unit calculations, not performance guarantees. They assume the stated energy is available at the stated constant output, without additional losses or operating limits. A project announcement needs its own specifications before the example can describe its equipment.
For the definitions, consult the EIA’s electricity-units explanation and the IEA’s capacity glossary entry. When comparing projects, retain the unit and the time period alongside the number. In the daily-load example, 1,200 MWh divided by 24 hours gives 50 MW average power; dividing it by 12 hours gives 100 MW. The energy total is identical, but the implied operating rate is different.
