The most commonly used unit to measure electrical power is the kilowatt-hour (kwh), meaning one kilowatt (1,000 watts) of electricity produced or consumed in one hour. A 50-watt light bulb left on for 20 hours consumes one kwh.
According to the American Wind Energy Association, the output of a wind turbine depends on the turbine's size and the speed of the wind moving through its rotors. Modern turbines have power ratings ranging from 250 watts to 5 MW.
The power consumed by an average household, about 10,000 kwh per year, can be produced by a 10-kw turbine if it's located at a site that has an average wind speed of 12 miles per hour. A five-megawatt (MW, 1 million watts) turbine, on the other hand, can produce more than 15 million kwh per year at that site. That is enough to power more than 1,400 households.
Because wind speed is a major component in determining a turbine's output, a wind resource assessment of a potential site has to be done prior to erecting a turbine. Generally, a small electric turbine (as opposed to a water-pumping turbine, which requires less wind) needs an average wind speed of 9 mph per year and utility-scale wind power plants require a minimum annual average of 13 mph.