When describing electricity production, the terms electric power (or capacity) and electric energy (or electricity) are often used. “Power” is the ability to do work and “energy” is the actual performance of the work, or the use of that ability over a period of time. The distinction is like a person’s ability to lift weights and the actual lifting of the weights; although they have the capacity to lift the weights, until they actually lift them, they do not expend the energy.
The unit used in this text for electric power, or capacity, is the megawatt. The unit used for electric energy, or electricity, is the kilowatthour. It takes 60 watts of capacity to power a 60watt lightbulb. To light a 60watt lightbulb for 1,000 hours requires 60,000 watthours of electricity, or 60 kilowatthours. To power 1 million 60watt lightbulbs, 60 megawatts of capacity is required.
The distinction between capacity and electricity is important. A wind turbine, for instance, might have a 1kilowatt capacity, but its electricity production per day in kilowatthours depends on how often and how strongly the wind blows. If a strong wind blows for 24 hours, the wind turbine will produce 24 kilowatthours; if the wind only blows strongly for 8 hours and doesn’t blow at all the rest of the day, the wind turbine will produce 8 kilowatthours of electricity.