Wind Speed Calculator
Do not operate the form until this page and its programme have loaded completely.
Enter your wind speed measurement in any column at the appropriate height, e.g. 10 metres. Then click outside the field, click Submit, or use the tab key. The programme will then calculate wind speeds for other heights. You may plot your results in a separate window by clicking on Plot in the appropriate column. (If the plot window disappears, it is probably hidden behind this window).
CALCULATOR
roughness
- class
- length m

0.0
0.0002

0.5
0.0024

1.0
0.03

1.5
0.055

2.0
0.1

3.0
0.4

4.0
1.6
150 m
140 m
130 m
120 m
110 m
100 m
90 m
80 m
70 m
60 m
50 m
40 m
30 m
20 m
10 m
Plot Plot Plot Plot Plot Plot Plot



Average wind speeds are often available from meteorological observations measured at a height of 10 metres. Hub heights of modern 600 to 1,500 kW wind turbines are usually 40 to 80 metres, however. The spreadsheet will calculate average wind speeds at different heights and roughness classes. Just enter a wind speed measured at a certain height for a given roughness class and click the Submit button.
Please note, that the results are not strictly valid if there are obstacles close to the wind turbine (or the point of meteorological measurement) at or above the specified hub height. ["close" means anything up to one kilometre].
You should also note, that there may be inverse wind shear on hilltops because of the hill effect , i.e. the wind speed may actually decline with increasing height during a certain height interval above the hilltop. You should consult the European Wind Atlas mentioned in the bibliography in the Reference Manual for further information on this phenomenon.
Take a look at the example below the table to make sure you understand how it works, before you start entering your data. More accurate and extensive roughness definitions may be found in the units section.
An Example
As an example, have a look at the spreadsheet above. We have already entered 10 m/s at 100 m height in roughness class 2. You will notice that the wind speed declines as you approach ground level. You will also notice that it declines more rapidly in rough terrain.
Remember that the energy content of the wind varies with the third power of the wind speed. If you look at the column with roughness class 2, you will see that wind speeds declines 10 per cent going from 100 metres to 50 metres. But the power of the wind declines to 0.9 3 = 0.73, i.e. by 27 per cent. (From 613 to 447 W/m 2 ).
If you compare the wind speeds below 100 m in roughness class 2 with roughness class 1, you will notice that for a given height the wind speeds are lower everywhere in roughness class 2.
If you have a wind turbine in roughness class 2, you may consider whether it is worthwhile to invest 15,000 USD extra to get a 60 metre tower instead of a 50 metre tower. In the table you can see that it will give you 2.9 per cent more wind, and you can calculate, that it will give you 9 per cent more wind energy.
You can solve this problem once you have learned how the turbine electricity production varies with the available wind energy. We will return to that question when you have learned to use the power density calculator and the wind energy economics calculator.
Now, try the calculator for yourself.
© Copyright 1997-2003 Danish Wind Industry Association
Updated 18 May 2003
http://www.windpower.org/en/tour/wres/calculat.htm
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