Megawatts and megawatt-hoursMW, MWh
Megawatts measure power: the rate of generation, consumption or battery charging. Megawatt-hours measure energy over time. A steady 4 MW for 15 minutes delivers 1 MWh. A battery's MW rating and MWh capacity describe different limits.
How it works
Power is a rate. One megawatt is 1,000 kilowatts. Energy is the amount generated or used over a period: energy in MWh = average power in MW × time in hours. One MWh equals 1,000 kWh. If power changes during a period, use its average for that period or add the energy from shorter intervals.
A generator's MW rating describes its rated power, not how much energy it will produce in a year. Weather, downtime and operating limits affect annual MWh. Batteries need both ratings: MW limits charging or discharging power, while MWh describes stored or deliverable energy on a stated measurement basis. Usable capacity, efficiency and operating reserves affect how long the battery can sustain its rated power.
Why it matters
Confusing MW and MWh changes a project's size, its cost and its commitments. Market schedules often specify MW for a delivery block, while settlement pays for MWh. Storage proposals should state power, energy, measurement point and usable capacity so their durations can be compared.
A worked example
A plant exporting an average 40 MW for a 15-minute block delivers 40 × 0.25 = 10 MWh. At $50/MWh, that earns $500. A battery with 20 MW of discharge power and 80 MWh of usable energy measured at the same output point can discharge at full power for 80 ÷ 20 = four hours, assuming no additional reserve is held back.
Illustrative figures.