SODAR calibration for wind energy applications, final reporting on WP3, EU WISE project NNE5-2001-297

Bradley, SG; Antoniou, I; von Hünerbein, S; Kindler, D; Jorgensen, HE; De Noord, M

Abstract

The method traditionally used for measuring the wind speed and direction for wind energy purposes is to record the output from cup or propeller anemometers and vanes at several heights on a mast. As turbines have grown in height, this method has become increasingly more expensive and difficult, and new methods have been sought.

One alternative method for measurement of wind speed and direction over depths of around 200m is the SODAR (SOund Detection And Ranging). This instrument is installed on the ground and every few seconds transmits a short pulse of sound upward into the atmosphere. As the sound propagates upward, some acoustic energy is continuously reflected back to the ground by the variable atmospheric turbulence encountered. By analysing the Doppler frequency shift of echoes received from sound transmitted at a small angle to the vertical, wind speed components are estimated as a function of height.

SODAR technology is well established as a tool for visualising and quantifying atmospheric dynamics in the lowest few hundred meters. At the same time, use of SODAR technology as a replacement for cup or propeller measurements in wind energy applications has a number of potential drawbacks. These include the need to calibrate much more rigorously than generally required for other applications, and the requirement that the SODAR operates with well-specified performance over the full range of atmospheric conditions relevant to wind turbine operations. Furthermore, SODAR performance should be portable from one physical site to another, and instruments supplied by a variety of manufacturers should be able to be deployed with known characteristics.

Within the WISE (WInd energy SODAR Evaluation) project (EU project number NNE5-2001-297), work package WP3 described in this report, is concerned with:
a) An estimation of the uncertainties in calibration which arise from SODAR design and operation.
b) Description of calibration procedures established by the WISE project and an evaluation of their limitations.
c) Testing of the calibration procedures against other methods of measurement.
d) Suggestions for improvements in SODAR design.
Items (a), (b), and (c) comprise Project deliverable D4 (Report on calibration of SODAR and inter-comparison before and after calibration). Item (d) comprises Project deliverable D5 (Notes on possible improvements of SODAR hardware/software for easier and better calibration).

The central conclusions of this work are
1. Care and understanding of SODAR error sources are required in order to adequately calibrate SODARs
2. A reliable calibration method is to calibrate a SODAR against a cup anemometer mounted at the top of a 40 m mast, and to use this calibration to correct SODAR wind speeds at other heights.
3. When compared with quality cup anemometers, corrected SODAR wind speeds show similar rms fluctuations to those exhibited between two cup anemometers
4. SODAR wind directions show good agreement with mast mounted vanes
5. Variations between SODARs of the same design appear to be small
6. Design changes could improve SODAR operation for wind energy applications.

Citation

Bradley, S., Antoniou, I., von Hünerbein, S., Kindler, D., Jorgensen, H., & De Noord, M. (2005). SODAR calibration for wind energy applications, final reporting on WP3, EU WISE project NNE5-2001-297

• Report Type: Project Report
• Publication Date: Mar 1, 2005
• Deposit Date: Aug 19, 2010
• Publicly Available Date: Apr 5, 2016
• Pages: 68
• ISBN: 0954164911