LIDAR SUPPLEMENT Stuart Bradley


Physics Department, University of Auckland, New Zealand Torben Mikkelsen


Wind Energy Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark


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Lidar remote sensing


Research on wind measurement for wind energy currently focuses on new remote sensing technologies for site-specific wind measurements and for real-time turbine-integrated monitoring and control. Wind measurement methodologies are progressing from point measurements, obtained from in-situ instruments mounted on vertical masts, towards wind profiles and entire wind fields retrieved from remote sensing instruments placed on the ground or integrated within the turbines themselves. However, mast mounted in-situ instruments are still used for reference measurements (cup anemometers are the standard, but also sonic anemometers are in wide use).


The remote sensing instruments used for wind energy today are lidars (based on laser energy reflections back to the instrument from atmospheric particles) and sodars (based on acoustic energy reflections back to the instrument from turbulent fluctuations). Lidars and sodars share many common geometric and signal processing features, and both are challenged by large sampling volumes and/or diminishing reflected power with increasing distance to the measurement volume. Nevertheless, extremely high accuracies are now possible, particularly from lidars, and many exciting possibilities are opening up. In this, our second review article this year on remote sensing1, we now report on recent


and planned lidar remote sensing research and development activities in connection with wind energy.


Proof of lidar wind measurement concept Recently, in June 2011, a hitherto unparalleled demonstration of wind lidar performance was obtained in the calibrated wind tunnel belonging to LM Wind Power, Kolding Denmark.


www.internationalsustainableenergy.com The laser beam from renewable energy


consultancy Natural Power’s continuous wave ZephIR 300 wind lidar was re-directed via a small fibre-fed telescope into LM Wind Power’s


These new calibrated wind tunnel


measurements conclusively show that a wind lidar is capable of making high accuracy wind measurements.


Latest results from EU UpWind WP6 remote sensing group UpWind was a European Commission funded project that ran from 2006 to 2011. UpWind’s overall aim was to look towards the future design of very large wind turbines (5-10MW) for onshore and offshore. The final report was published in March 2011 (www.upwind.eu). Sub-task “WP6” on remote sensing was


motivated by the continuous growth in wind turbine size, which makes mast-mounted conventional wind instrument installations for reference measurements more and more costly and cumbersome. The work package looked at testing, improving and developing remote sensing methodologies for more accurate wind profiling, for wind condition assessment, for resource assessments, and for better wind turbine control.


Figure 1Wind tunnel mached performance testing of lidar


» Over the past decade, lidars based on the ‘coherent detection’ principle have appeared on the wind energy market «


calibrated wind tunnel in Denmark. Wind speeds from 5m/s to 75 m/s were measured by the lidar and a calibrated pitot, with an averaged difference of just 0.4 per cent (see Figure 1).


Wind lidars Lidars measure the wind speed at remote distances by transmission of coherent laser light that, when backscattered from aerosols (dust) suspended in the air flow, becomes Doppler-shifted (changes color) proportional to the speed of the aerosol. Since the aerosol moves with the air, the lidar records the speed of the air flow in the measurement volume. Over the past decade, lidars based on the


International Sustainable Energy Review Volume 5, Issue 3, 2011


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