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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Remote sensing: From toys to tools?' taking place on Wednesday, 12 March 2014 at 14:15-15:45. The meet-the-authors will take place in the poster area.

John Medley Zephir Ltd, United Kingdom
Co-authors:
John Medley (1) F P
(1) Zephir Ltd, Hollybush, Ledbury, United Kingdom

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

John Medley is a Chartered Engineer with over 20 years experience of making and analyzing electromagnetic measurements. He has an Honours Degree in Mathematics and a Masters in Mathematical Modelling from the Universities of Bristol and Loughborough respectively. He received the IET’s Measurement prize in 1995 while working for the UK’s National Physical Laboratory, before spending 12 years in the radar industry. Since 2011 he has worked as a data analyst with ZephIR Lidar and is especially interested in optimizing algorithms for lidar data processing.

Abstract

Evaluation of wind flow with a nacelle-mounted, continuous wave wind lidar

Introduction

Nacelle-mounted lidar is becoming widely recognized as a tool with potential for assessing power curves, understanding wind flow characteristics, and controlling turbines. As rotor diameters continue to increase, and the deployment of turbines in complex terrain becomes more widespread, knowledge of the incident wind field beyond the mean speed and direction at hub height become essential, for example, in the calculation of rotor-equivalent power curves. The use of a scanned, continuous wave lidar can provide a wealth of such information and this paper contains comparisons of lidar measurements such as shear, veer and turbulence, to a high-quality traditional mast.

Approach

A ZephIR Dual-Mode lidar (capable of both vertical, ground-based, and horizontal, turbine-mounted operation) was installed on the nacelle of a Nordtank 500 kW turbine on the Risø campus of the Technical University of Denmark (DTU) for approximately 5 months, starting in December 2012. Lidar data were acquired at several ranges, corrected for the effects of tilt, and processed to give detailed information about the upwind flow. Direction-filtered results were compared with measurements from a high-quality met mast situated approximately 90 m (2.2 rotor diameters) to the west. SCADA data from the turbine were used to generate power curves.

Main body of abstract

The ZephIR lidar measures 50 line-of-sight velocities around each 1-second circular scan, at user-selected measurement ranges. Real time attitude sensors in the ZephIR record inclination and roll to allow measurement correction for nacelle movement. This wealth of lidar data allowed a number of processing methods to be analyzed and compared. The measured (10-minute averaged) wind speeds and directions exhibited excellent correlation with results from the instrumentation on the traditional met mast.
Vertical wind shear and veer can be derived from each 1-second scan of the lidar. The accuracy and precision achieved for these derived quantities will be discussed.
It is well known that a lidar measures turbulence intensity (TI) with mixed wind components on a different scale to a cup anemometer, primarily due to volume averaging effects. TI measured with both lidar and the mast anemometers will be compared and their relative merits discussed.
Finally, the lidar measurements have been used to derive turbine power curves using rotor-equivalent wind speeds, accounting for the effects of shear, veer and turbulence intensity as described in IEC 61400-12-1 CD.
The lidar-generated power curve compares very favourably with an equivalent curve generated from the mast data only. This provides strong evidence that a turbine-mounted continuous wave lidar can be used to perform high quality assessments of turbine performance, with potentially less restriction on wind direction, and hence shorter measurement campaigns.
We believe that this is the first time that a commercially available, turbine-mounted lidar has been used to derive such rotor-equivalent power curves.


Conclusion

The results contained in this paper indicate that high fidelity turbine-mounted measurements of several characteristics of the wind flow around the full rotor disc can be obtained with a scanned, continuous wave wind lidar. The suitability of the technique for evaluating power curves that account for wind shear, veer and turbulence has been evaluated. The reliability of the measurement data, and the full coverage of the wind turbine rotor area, improve confidence in the application of this technique for other critical tasks, such as turbine control for fatigue load reduction and power output optimisation.


Learning objectives
Delegates will gain a good understanding of the capabilities that scanned, continuous wave lidar can offer in a nacelle-mounted deployment, which is currently an area of great interest and rapid development. The results will give a good indication of the likely uncertainties in such measurements, how they compare with traditional techniques, and hence the suitability of the use of nacelle mounted wind lidar for applications such as power curve measurement and turbine control.