Class A & Class C: These two anemometer classes vary only in the air temperature requirements. They both meet strict terrain topology requirements for wind energy production and both have only a ±3° wind upflow requirement. The air temperature influence on MeteoWind 2 is less than 1.1% between -20°C and +40°C, even without heating, which is quite good compared to the status quo.

Class B & Class D: These two anemometer classes also vary only in the air temperature requirements. They do not conform to terrain topology requirements for wind energy production and both have a wide ±15° variation of wind upflow. You can see from the following plot, the tilt angle upflow and downflow sensitivity of MeteoWind 2 anemometer.

Anemometer Requirements for Wind Resource Assessment

Wind speed measurements shall be made with a cup anemometer that meets the requirements in Annex I. For power performance measurements an anemometer with a class better than 1,7A shall be used. Additionally, in terrain that does not meet the requirements of Annex B for not requiring a site calibration, it is recommended that a class better than class 2,5B or 1,7S be used. The wind speed to be measured is defined as the average magnitude of the horizontal component of the instantaneous wind velocity vector2, including only the longitudinal and lateral, but not the vertical, turbulence components. Consequently, the angular response of the cup anemometer should be cosine shaped (see Annex J). All reported wind speeds, and all uncertainties connected to operational characteristics shall be related to this wind speed definition.

The cup anemometer shall be calibrated before and recalibrated after the measurement campaign. The difference between the regression lines of calibration and recalibration shall be within ±0,1 m/s in the range 6m/s to 12 m/s. Only the calibration before the measurement campaign shall be used for the performance test. Calibration of the cup anemometer shall be made according to the procedure of Annex F. During calibration the cup anemometer shall be mounted on a vertical tube configuration similar to the one being used during the power performance test.