To show the information about the distributions of wind speeds, and the frequency of the varying wind directions, one may draw a so-called wind rose on the basis of meteorological observations of wind speeds and wind directions.

A look at the wind rose is extremely useful for siting wind turbines. If a large share of the energy in the wind comes from a particular direction, then you will want to have as few obstacles as possible, and as smooth a terrain as possible in that direction, when you place wind turbines in the landscape. In these examples most of the energy comes from the West by Northwest. We therefore need not be very concerned about obstacles to the East or Southeast of wind turbines, since practically no wind energy would come from those directions. You should note, however, that wind patterns may vary from year to year, and the energy content may vary (typically by some ten per cent) from year to year, so it is best to have observations from several years to make a credible average. Planners of large wind parks will usually rely on one year of local measurements, and then use long-term meteorological observations from nearby weather stations to adjust their measurements to obtain a reliable long term average.

Since we know that the energy content of the wind varies with the cube (the third power) of the average wind speed it is important that we know the "Frequency Distribution" to correctly select the optimal turbine to convert this energy at our site.

The graph above clearly illustrates that the majority of the wind energy available at this test site is in the 23mph to 29mph range and great care should be taken to make turbine selections accordingly. We can use this graph to quickly see that although our site only has a 26mph wind approximately 2.6% of the time the available energy in this range is much greater.

Diurnal wind speed pattern.

Average hourly wind speeds.