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LIDAR FOR WIND ENERGY


FEATURE


Pulsed laser


diodes and avalanche photodiodes can be used as the respective light source and detector technology


usually require less than two per cent error for wind speed and less than five degrees error for direction, which Flidar provides. The engineers also need high data availability; typically more than 80 per cent, says Douglas.


Detector technology


Pulsed laser diodes and avalanche photodiodes can be used as the respective light source and detector technology in lidar systems, according to Stuart Nunn at Laser Components, which supply both for lidar systems.


In terms of the light source, pulsed laser diodes have the advantage of low cost compared to diode-pumped solid-state lasers. A pulsed laser will also have a high peak power compared to a continuous wave laser, which equates to a stronger returning signal, explains Nunn. This is important when being able to detect light returning from a height of 280m – this requires both a reasonably strong returning signal and a sensitive detector. And avalanche photodiodes (APDs) are sensitive, fast, and have a large detection area to detect the returning signal.


‘Over those distances [hundreds of


metres], you’d need an APD [to detect the signal],’ states Nunn.


A lidar system in front of a wind turbine. Lidar can measure wind speeds at heights up to the tip of turbine blades and above


APDs have an avalanche effect within the semiconductor material, which multiplies the electrical signal produced from each photon hitting the detector. Therefore, they have a much higher sensitivity than a photodiode. Turbulence is another factor that has to be taken into consideration when choosing a site for wind turbines, largely because it affects the load on the turbine. Gusts too strong


➤ PHOTONICS FOR RENEWABLE ENERGY 2013 13


Technical University of Denmark


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