A megawatt (MW) and a megawatt hour (MWh) are useful units for measuring large amounts of electricity.
A megawatt is a measurement of instantaneous power typically used to measure the output of a power source. One megawatt (MW) = 1,000 kilowatts (kW) = 1,000,000 watts (W). A 1-megawatt solar array, for example, is able to produce up to 1 megawatt of power in any instant (assuming the array is operating at peak conditions).
A megawatt-hour is a measure of the total amount of energy consumed over a period of time. One megawatt-hour (MWh) is one hour of using electricity at a rate of 1,000 kilowatts. A building that consumes 1 megawatt of electricity for four hours would consume a total of 4 megawatt-hours of energy.
A kilowatt-hour (kWh) is one hour of using electricity at a rate of 1,000 watts. Your utility measures your energy consumption in terms of kWh. Your building draws a certain number of kilowatts (kW) from the grid each moment to power itself. So if you draw 10 kW of power for 10 hours, you have consumed 100 kilowatt-hours of energy.
Understanding the scale of megawatt and megawatt-hour
A typical large office building (100k square feet or larger) uses on average 20 kilowatt-hours of power per square foot per year. So, a 100,000-square-foot building would use 2000 MWh of power per year (20 kWh / sqft * 100,000 sqft = 2,000,000 kWh = 2000 MWh), 5.48 MWh a day (2000 MWh/365 days).
Why this matters
The amount of energy your building uses and the cost of that energy are important factors in determining the right clean energy solution for your needs. Every provider bidding on your project will propose a solution that includes the annual energy production of the system in MWh and the cost per W or kWh. Understanding these units of measurement will be helpful when evaluating your bids.