Wind speed is a crucial element in projecting turbine performance, and a site's wind speed is measured through wind resource assessment prior to a wind system's construction. To put it into perspective a 100 watt light bulb left on 5 hours a day will consume 15 kilo-watt hours per month. This means that increasing the average wind speed from 6 m/s to 7 m/s results in 60% more power from the same turbine and an increase in annual energy production of 36%. the minimum wind speed at which the wind turbine will generate usable power. A small home turbine like the Southwest Air Breeze will produce 38 kilowatt-hours per month with a 12mph consistent wind speed or about 4% of what a home needs. The wind speed when wind turbines start producing electricity is called cut-in wind speed. This wind speed is typically between 7 and 10 mph for most turbines. Wind speed within a preferred range can produce a significant amount of electricity with certain small wind turbine models. About 14 to 22 kilometres per hour (4 to 6 metres per second) is generally the preferred wind speed. The amount of power generated by a wind turbine is proportional to the cube of the wind speed.