The megawatt-hour (symbol: MWh) is a unit for measuring energy. It corresponds to one megawatt (MW) of power being used over a period of one hour. Since a watt is an amount of energy over a timespan (joule per second), multiplying it with a timespan gives an energy amount (1 J/s × 1 s = 1 J).

The megawatt-hour is commonly used for electrical energy, since it may be easier to understand in a practical context than the proper SI unit for energy, the joule, which is a watt-second (W·s). The joule is a comparatively small unit, making numbers quite large.

Identities

• 1 MW·h = 3,600,000,000 J
• 1 W·h = 3,600 J
• 1 W·s = 1 J
• 1 W = 1 J/s

A 60 W light bulb consumes 60 W, 60 J/s, 216,000 J/h, 60 W·s per second, 60 W·h per hour.

The relationship between power (P), energy (E) and time (t) is given by the formula:

If we use SI units,

• P is given in watts
• and t is given in seconds
• then E is in joules

If

• P is given in megawatts
• and t is given in hours
• then E is in megawatt hours