Analysis of calibration results from cup and propeller anemometers. Influence on wind turbine Annual Energy Production (AEP) calculations

Abstract

The calibration coefficients of several models of cup and propeller anemometers were analysed. The analysis was based on a series of laboratory calibrations between January 2003 and August 2007. Mean and standard deviation values of calibration coefficients from the anemometers studied were included. Two calibration procedures were used and compared. In the first, recommended by the Measuring Network of Wind Energy Institutes (MEASNET), 13 measurement points were taken over a wind speed range of 4 to 16 ms" 1 . In the second procedure, 9 measurement points were taken over a wider speed range of 4 to 23 m s _1. Results indicated no significant differences between the two calibration procedures applied to the same anemometer in terms of measured wind speed and wind turbines' Annual Energy Production (AEP). The influence of the cup anemometers' design on the calibration coefficients was also analysed. The results revealed that the slope of the calibration curve, if based on the rotation frequency and not the anemometer's output frequency, seemed to depend on the cup center rotation radius.

Deviation of Cup and Propeller Anemometer Calibration Results with Air Density

“…The accuracy of an anemometer is assured by its periodic calibration in a wind tunnel [3]. As a result of this calibration process it is possible to obtain the coefficients A and B of the anemometer's transfer function:…”

“…In a previous study [3], based on series of calibrations from January 2003 to August 2007, the influence of the wind speed range and some anemometer geometrical parameters on the calibrations results was studied. In a second analysis campaign, the deviation over time of cup anemometer calibrations results from initial values was studied.…”

“…This facility is an open-circuit wind tunnel with a closed test section measuring 0.9 by 0.9 m. It is served by four 7.5 kW fans with a flow uniformity better than 0.2% in the testing area. More details concerning the facility and the calibration process are included in reference [3]. The calibrations analyzed in the present paper were performed following the MEASNET recommendations (over 13 points and 4 to 16 m s −1 ).…”

“…A list of the anemometer models studied are included in Table 1, together with the number of calibrations analyzed and the period of time in which these calibrations where performed. More detailed information with regard to the geometrical and other characteristics of these anemometers can be found in reference [3]. Only anemometer models that were calibrated at least 150 times at the IDR/UPM from March 2003 to February 2011 were considered in the present work, in order to have statistically more significant results.…”

“…From these results it seems that the variations of measured wind speed due to a change in the air density ∆ρ = 0.1 kg·m −3 , could be relevant. In Table 7a and b, the Annual Energy Production (AEP) of a 2.5 MW wind turbine (GE2.5, see Reference [3] for more information) has been estimated for 4, 7, and 10 m s −1 annual average wind speed. It should also be said that taking into account that the air density variation with regard to the data in Figure 2 and Figure 3 is ∆ρ ~ 0.05 kg·m −3 , the AEP estimations for ∆ρ = 0.1 kg·m −3 can be considered a rough extrapolation.…”