The watt-hour is a unit of energy equal to one watt of output for an hour. It is equal to 3,600 joules. While the watt is the SI unit of power, electrical power consumption is usually measured in Kilowatt-hours for a household. Electrical energy generated by a power plant is often measured in TWh (over the course of a year). This idea is closely related to the watt-year (or the more commonly used GWy).
A kilowatt-hour is a unit of energy equal to outputting one thousand watts for one hour. It is equal to 3,600,000 Joules. The kilowatt hour is the unit of measurement for a residential power bill, and we usually use kilowatt hours for personal energy use. It is abbreviated kWh.
A terawatt-hour is a unit of energy equal to outputting one trillion watts for one hour. It is equal to 3.6x1015 Joules. This value is large enough to express annual electricity generation for entire countries, and is often used when describing major energy production or consumption.
To read more about the watt-hour, click here.
To read more about the kilowatt-hour, click here