Variations in the short time scale usually are not very important for evaluating the wind resource unless the wind is very turbulent or frequently changes direction. For single wind turbines, abrupt wind speed changes can cause large fluctuations in power output. In wind power plants that contain many wind turbines, however, this effect tends to average out because wind machines at different locations experience gusts at different times. For this reason, wind speed measurements intended to evaluate a potential wind power site normally are averaged over a period of 10 minutes to one hour. However, unusually gusty or turbulent winds can cause extra wear on wind turbine components and increase repair and maintenance costs.
Variations occurring over hours to days are very important for wind resource evaluation.
Wind speed records typically show large upswings and downswings that persist for up to several days, reflecting passing storms and weather fronts. In addition, many locations experience a daily pattern of wind speed variation, with peak winds often occurring in the afternoon. Monthly and seasonal variations also have a significant effect on wind power plant performance. The degree and timing of seasonal variations depend upon the region. In most parts of the United States, winds are stronger in winter and spring because of more frequent storms and greater high-altitude wind speeds.