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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.

Raghu Krishnamurthy LEOSPHERE, France
Co-authors:
Raghu Krishnamurthy (1) F P Matthieu Boquet (1)
(1) LEOSPHERE, Orsay, France

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Abstract

Turbulence intensity measurements from a variety of doppler lidar instruments

Introduction

Several types of lidars are currently being used in the industry for wind resources assessment and siting, depending on the location (i.e., offshore or onshore). The ability of various types of lidars, such as, Lidar profilers, scanning Doppler lidars and buoy lidars, to measure turbulence is evaluated. This could provide wind farm developers an ability to create a 3D box of turbulence measurements surrounding a wind farm. The ability to choose various remote sensing devices, for optimal wind farm siting, based on the advantages of each instrument will be presented.

Approach

Conglomeration of measurements from several campaign studies have been analysed to calculate 10 minute averaged turbulence intensity. The turbulence estimated from WINDCUBE V2 lidar profilers and scanning Doppler lidars are compared to tower measurements, while several advanced simulations performed for assessing buoy lidars performance is used to simulate the quality of turbulence estimated by buoy lidars. The accuracy of turbulence measured at several heights, for various atmospheric and terrain conditions is analysed.

Main body of abstract

The effect of turbulence on wind turbines is difficult to quantify, and would result in an increase or decrease of wind turbine power based on atmospheric conditions. Several studies have shown a negative impact on wind turbine fatigue loads due to increase in turbulence. In this paper, the accuracy of turbulence intensity measurements from a variety of lidar measurements such as, lidar profilers, scanning coherent Doppler lidars (CDLs) and buoy based lidars will be presented. Ten-minute averaged turbulence intensity estimates from lidar profilers and scanning coherent Doppler lidars are compared to tower estimates at various heights. The effect of lidar estimated turbulence intensity in several terrain and atmospheric conditions (thermal stability) is evaluated. Sample turbulence intensity estimates from buoy lidar simulations, after accounting for motion compensation effects of the buoy lidar, are presented. Spatial turbulence measurements could be a valuable input for wind farm developers for wind farm site selection and a valuable input into improving various CFD or meso-scale models. The effect of volume averaged turbulence, compared to point turbulence is also evaluated.

Conclusion

The accuracy of turbulence intensity from various lidar measurements compare well with tower measurements and the trade-off between spatial turbulence measured by lidar and point turbulence is shown to be critical. The effect of various terrain and thermal stability conditions provided a better understanding of the current expectation level of turbulence measured by various types of Doppler lidars.


Learning objectives
The EWEA audience would get a deeper understanding of various types of lidars and their accuracy, currently available in the market. The audience would be able to assess the advantages and disadvantages of instruments for site assessment. Also help visualize the advantage of using multiple lidar measurements simultaneously across the site for a 3-dimensional understanding of the turbulence behaviour observed at the site.