Utility-scale wind turbines are tall enough to experience the effects of windshear. = the wind speed at the hub height of the wind turbine [m/s] U anem = the wind speed at anemometer height [m/s] z hub = the hub height of the wind turbine [m] z anem = the anemometer height [m] z 0 = the surface roughness length [m] ln(..) = the natural logarithm

Hub heights of modern 600 to 1,500 kW wind turbines are usually 40 to 80 metres, however. The calculation procedure can be automated by a weather monitoring system, assuming it comes with advanced data processing functions.

Hub heights of modern 600 to 1,500 kW wind turbines are usually 40 to 80 m, however. The programme will then calculate wind speeds for other heights. These obstacles have an effect for several dozen meters above ground level, since the wind is made of molecules that slow each other down.Wind can flow freely at altitudes where ground-level obstacles and terrain features no longer have an effect. Average wind speeds are often available from meteorological observations measured at a height of 10 metres. The spreadsheet will calculate average wind speeds at different heights and roughness classes. Note that the wind is not only influenced by obstacles and terrain features at the site where it is being measured. Enter a value in the Power law exponent box.= the wind speed at the hub height of the wind turbine [m/s]= the wind speed at the hub height of the wind turbine [m/s] The spreadsheet will calculate average wind speeds at different heights and roughness classes. However, there is another variation that is much less evident: wind conditions also change with altitude.

For instance, a measurement taken 20 metres above ground level will yield a different result than one taken 50 meters over the same spot.

10 metres. This increases cost due to the extra material, and the tower must be sturdier to account for the stronger wind at higher altitude.When wind speed is measured, it is important to specify the height at which the anemometer is installed. The following are some common examples: Structural engineers must determine the wind load, which cannot be described with a single wind speed value. You may plot your results in a separate window by clicking on Plot in the appropriate column.

Large-scale wind patterns are influenced by geographical features.Weather scientists have studied windshear in depth, developing many mathematical models to describe it. In general, wind speed increases faster in proportion to altitude when there are less obstacles and uneven terrain around.Windshear is minimal out it the sea, far from the coast, since there are no obstacles above sea level disrupting the wind.A city with skyscrapers would be the opposite scenario - the disruption of natural wind patterns can extend several hundred metres above ground level.A field with trees and small hills would be an intermediate case. Then click outside the field, click Submit, or use the tab key. Experience is also very important: you will want to work with a provider that has an established track record in weather monitoring.Sign up to get the latest on sales, new releases and more … This value ranges from less than one millimeter in the open sea, to several meters in urban locations.Marine wind turbines are such a promising concept because the impact of terrain is eliminated almost completely: with no obstacles around, favorable wind speeds can be found at lower altitudes. When no height value is provided, it is normally assumed that the measurement was taken at 10 metres.You may recall from high school mathematics that you can calculate the slope of a linear graph using two points along the line. Although this approach does not provide the same accuracy as measuring wind speed and direction at the required height, the confidence is over 95% if the method is used correctly.

This wind variation with altitude is called Unless the wind is being blocked by a tall obstacle, its speed increases with altitude.

Due to their complexity, wind patterns are impossible to describe with a single concept or numerical value.

If you have two wind speed values for a given location at different altitudes, you can estimate speed for other height values, applying the mathematical models developed by weather scientists. Under the Variation with Height tab on the Wind Resource page, you can describe the way the wind speed increases with height above ground.

(If the plot window disappears, it is probably hidden behind this window). This variation of wind speed with height is called wind shear. Wind speed researchers have found that, in practice, the power law exponent depends on terrain roughness, atmospheric stability, and several other factors. If obstacles are tall, such as the skyscrapers in cities, their effect disappears at a higher altitude.Between these extremes, wind speed increases gradually the higher you go. Wind patterns are unique for each site, but they are determined by common physical principles.At ground level, the wind slows down due to friction with objects and terrain features. Turbine blades sweep a very large area, and wind speed is higher for the area above the rotation axis.How to Determine Wind Speed for Multiple Height ValuesIn theory, you could account for windshear by measuring the wind at multiple heights. A similar principle applies for windshear, but just keep in mind that the math is much more complex! If you have two wind speed values for a given location at different altitudes, you can estimate speed for other height values, applying the mathematical models developed by weather scientists. This enables the use of shorter and less expensive towers. It is common knowledge that wind speed varies from site to site, and also that it changes over time for a given location. The following equation therefore gives the ratio of the wind speed at hub height to the wind speed at anemometer height:The surface roughness length is a parameter that characterizes the roughness of the surrounding terrain.