The aim of the wind measurement is to give a precise estimate of the energy yield on a specific site. The basic data needed are :
mean wind sped ( 10 mn average)
wind speed standard deviation (10 mn)
max wind speed over 10 mn
A number of samples are collected over a period of 10 mn. From these samples, the datalogger calculates the average and standard deviation and store the results. Normally, the sample is taken every second, ie 600 data over 10 mn. This sample duration is dependent on the characteristics of the anemometer.
The sensors
There is a number of wind sensors (anemometers), and the more common use rotating cups. The output signal is either a frequency or a voltage. The sensors are calibrated in a wind tunnel : this calibration is required every year to get full accuracy. For wind direction, th sensor (a wind vane) is typically a rotating potentiometer.
The measurement masts
The sensors are installed on a meausrment mast either self standing, either guyed. For a rough estimate, a 10 m mast could be sufficient, but for a detailed analysis higher towers are required up to 80 m. This tower is equipped with sensors at differnet heights in order to appreciate the wind shearon the site. The highest tower erected by EED is 100 meters high.
Correlation with meteo stations
Measurement data on the site over 6 or 12 months are correlated with data from existing meteo stations. Using the MCP method (Measure, Correlation, Prediction), it gives a long term estimate of the wind speed on the site.