Wind gust World Meteorological Organization. Any significant variation at this mean wind during the ten minutes preceding the observation are noted as gusts in messages such as METAR. It is generally reported in METAR when the peak wind speed reaches at least 16 knots and the variation in wind speed between the peaks and average wind is at least 9 to 10 knots. In marine meteorology, the top speed of a burst is expressed in meters per second (m/s) or in knots, while the Beaufort scale is used for reporting the mean speed. When the maximum speed exceeds the average speed by
Variable speed wind turbine As of 2003, nearly all grid-connected wind turbines operate at an exactly constant speed (synchronous generators) or within a few percents of constant speed (induction generators). Below is an illustration of the formula_8 curve for a typical wind turbine. Maximum efficiency occurs at one tip-speed ratio only. Since the tip-speed ratio is given by the aforementioned expression, variable speed wind turbines can operate at maximum efficiency over all wind speeds (ideally). For a wind turbine, the power harvested is given by the following formula: formula_9 where formula_10 is the power, formula_11 is the density of the air, formula_3 is the