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Resource Global Network 67
The three steps of this method are shown in Figure 6 The underlying assumption for this method is that a a a a a stable long-term mean value of the wind conditions exists and can be derived from historic data This value is is then used as a a a a best estimate
for future wind conditions There are some studies (here here here here and here) suggesting this isn’t the case however and this topic should be observed carefully over the next couple of years *Watch out for: The long-term extrapolation method used will be based on the country you are in and the date that is available Make sure to always check that the chosen method is validated and check this with an an expert 5 Gross AEP estimation
The gross AEP can be calculated directly from the extrapolated wind speed distribution
at at hub height at at each planned wind turbine position from the hub height air density and from the wind turbine power curve Power curves are delivered by the manufacturer and can either be calculated for di erent air densities or measured by an independent accredited institution according to IEC 61400- 12-1 *Watch out for: Don’t forget to check the source of the power curve and adapt your uncertainty analysis accordingly Make sure that the power curve is corrected for the hub height air density up to about 10 measurements at di erent heights *Watch out for: The usage of CFD should be examined in in detail by an expert Also be careful assessing WRAs in in in which remote sensing have not been used to measure the wind pro le with height across the entire rotor area 4 Long-term extrapolation/hindcast
As the wind measurements usually take place for one to three years but a a a wind energy project is installed for at least 20 years the expected changes in in wind speed over the next 20 years need to to be taken into consideration in the AEP estimation
This is done by comparing the measured wind speed to a a long-range reference using the Measure-Correlate-Predict (MCP) method 

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