megawatthours

Megawatt-hour, abbreviated MWh, is a unit of energy equal to the energy produced or consumed at a rate of one megawatt for one hour. Since 1 W equals 1 joule per second, 1 MWh equals 1,000 kilowatts × 1 hour, or 3.6 × 10^9 joules. It is also equal to 1,000 kilowatt-hours. The megawatt-hour is used to quantify electricity generation, transmission, and consumption over a period. By contrast, the megawatt (MW) is a unit of power, representing the rate of energy transfer at a given moment.

In energy markets and accounting, energy is frequently quoted in MWh or gigawatt-hours (GWh). For example, a plant rated at 50 MW that operates for 8 hours produces 400 MWh. A facility rated at 100 MW running for 24 hours yields 2,400 MWh. Storage and grid planning distinguish between capacity (in MWh, the amount of energy stored) and discharge rate (in MW, the maximum power that can be delivered).

Note on notation: MWh(e) is sometimes used to specify electrical energy, with MWh(th) used for thermal energy in contexts involving combined heat and power or district heating. Household electricity use is typically recorded in kWh, but large-scale accounts and inventories use MWh for convenience.