Back to the programme printer.gif Print




Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Optimising measurement strategies to maximise project value: Is the industry making false economies at the expense of project value?' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Michael Courtney DTU, Denmark
Co-authors:
Michael Courtney (1) F P
(1) DTU, Roskilde, Denmark (2) Leosphere , Orsay, France

Printer friendly version: printer.gif Print

Abstract

Optimized lidar scanning patterns for reduced project uncertainty

Introduction

In favourable conditions with a good viewpoint, shore-based scanning lidars can be used to measure the coastal wind resource out to about 10km. Since the lidar can scan arbitrarily, the wind resource at a number of different positions can be measured, giving information about the spatial variability of the resource. This paper looks at how the uncertainty of such sector-scanning measurements depends on the number of positions scanned. With this information it will be possible to optimize scanning patterns in future measurement campaigns in order to give the lowest overall project uncertainty.

Approach

A sector-scanning Doppler lidar was positioned 1.5km from an on-shore mast and sector-scanning measurements performed with the beams sweeping to coincide with the top of the mast. Horizontal wind speeds derived from the lidar measurements were compared to the mast measurements and the statistical uncertainty was calculated. The effect of multiple point measurements was simulated by omitting periods of data that would correspond to the scanner pointing at a different location and the increase in statistical uncertainty was observed.

Main body of abstract

Advances in scanning coherent Doppler lidar (CDL) devices have resulted in systems with longer range and durability, appropriate for long-term onshore and offshore wind energy campaigns. Retrieving accurate wind speed and direction are crucial for wind energy deployments, as they are the fundamental inputs for the evaluation of the potential energy yield of wind farms. Results from a WINDCUBE 200S (6.5km measurement range scanning lidar) deployed at the Danish Technical University (DTU), for a period of two months, are presented in this paper. Various scanning strategies were performed to test the accuracy of the wind speed retrievals. In this paper, the effect on wind speed uncertainty due to varying frequency of scanning CDL measurement at a given point in space will be presented. How much is the uncertainty of a point measurement increased if the beam scans over an area rather than just at the fixed point? Promising results are obtained, which will be valuable for the wind energy community in assessing the true potential of scanning CDLs to complement traditional wind resource assessment strategies, especially for large wind parks in coastal regions or in the vicinity of appropriate offshore observation sites. Scanning CDLs provide the flexibility to alter measurement locations at a later stage of the campaign for improved understanding of the wind flow around the site.

Conclusion

Scanning Doppler lidars can provide a variety of options for improved offshore and onshore wind resource assessment. We have obtained a first impression of how the uncertainty of each individual wind speed increases as the number of points scanned in the potential wind farm area also increases. This should assist future wind farm developers to plan measurement campaigns so as to maximize the benefit of the measurements by minimizing the total project uncertainty, thereby providing the best Return on Investment.


Learning objectives
The presentation will focus on the following topics:
1. Improve the understanding of Scanning CDL measurement method and strategies
2. Explain how scanning Doppler lidar can complement wind resource assessment studies