The difference between megawatts (MW) and megawatt-hours (MWh) often causes confusion, as these measurements describe entirely different physical properties of electricity. Understanding this distinction is necessary for accurate discussions of power generation, energy consumption, and the capacity of systems like solar farms and battery storage. The relationship between these units forms the basis for calculating energy output across the power grid.
What Megawatts Measure
A megawatt (MW) is a unit of power, representing the instantaneous rate at which electricity is generated or consumed. One megawatt equals one million watts, describing capacity or potential at a single moment in time. This is analogous to the speed of a car, such as 60 miles per hour, which indicates how fast the car is moving right now, not how far it has traveled. Power plants, wind turbines, and solar farms are rated by their maximum potential output in megawatts.
The MW rating defines the size of the electrical system’s flow capacity, similar to the diameter of a water pipe. A large industrial facility might require 5 MW of capacity to run all its machinery simultaneously. This measurement is about the “speed” of energy delivery and contains no reference to the total amount of energy delivered over time. Megawatts measure the moment-to-moment electrical demand on the power grid.
What Megawatt-Hours Measure
A megawatt-hour (MWh), in contrast, is a unit of energy, describing the total amount of work accumulated over a period of time. This measurement incorporates the time element, represented by the “h” for hour, into the power unit. The MWh is the standard unit for quantifying energy volume, similar to how distance measures the total travel accumulated by a car. It answers the question of how much energy was produced or consumed.
The MWh describes the total volume of electricity, making it the unit used on utility bills to charge customers for total consumption. One megawatt-hour is a substantial amount of energy, equivalent to keeping two modern refrigerators running for an entire year. This unit is the practical measure for calculating how long a specific power output can be maintained.
Calculating Energy Output
The conversion from megawatts to megawatt-hours is a calculation that incorporates time, not a simple unit conversion. The relationship is defined by the formula: Power (MW) multiplied by Time (hours) equals Energy (MWh). This calculation determines the total energy volume produced by a constant rate of power over a specific duration. One megawatt of power running continuously for one hour yields one megawatt-hour of energy.
For example, a solar farm with an average output of 5 MW operating for 10 hours will produce 50 MWh of total energy (5 MW x 10 hours). When the operational time is less than a full hour, the time must be converted into a decimal fraction of an hour. A power output of 2 MW maintained for 30 minutes is calculated as 2 MW multiplied by 0.5 hours, resulting in 1 MWh of energy.
Applying the Conversion to Real-World Examples
Understanding the MW to MWh relationship is fundamental to managing modern energy infrastructure. Power plants are rated by their MW capacity, indicating their maximum instant power delivery to the grid. Battery storage systems are dual-rated, describing both their instantaneous power output (MW) and their total storage duration (MWh). A battery rated at 750 MW / 3,000 MWh is designed to discharge its maximum power for four continuous hours.
The distinction is important in energy finance and planning, where utility companies use MWh to quantify the total electricity sold and consumed over a billing cycle. In energy policy, the MWh output of renewable sources is used to compare their contribution against conventional power sources. Knowing the conversion allows planners to accurately determine the required capacity (MW) needed to meet a projected energy demand (MWh) over a specific time period.