04 LIDAR SUPPLEMENT
‘coherent detection’ principle have appeared on the wind energy market. At first, they were designed to perform wind measurements over height ranges relevant to wind turbine applications. More recently their range has
turbines. The best lidars, of those investigated, measured wind speeds with accuracy close to that of cup anemometers.
For very large turbines, however, wind shear should be taken into consideration in
repeatability. Work is ongoing to amend IEC 61400-12-1 to account for the effect of shear, based on Wagner et al.’s ‘equivalent wind speed’ concept and allowing the use of remote sensing to measure wind profiles.
Lidars can provide profile measurements over the entire rotor plane, that can then be used for resource assessment over flat terrain. Power consumption is relatively low: today’s new 2nd generation wind lidars use significantly less than 100 Watt.
Wind speed assessment from lidars operating in complex terrain will require corrections that are now in principle well understood and that can be predicted if the local flow deflections can be modelled reasonably well.
3D short-range WindScanners at work (concept)
been extended so they can measure wind profiles even to the top of the atmospheric boundary layer (1-2 km), and enable wind resource mapping from a single ground-based installation out to 5-10 km distance.
» A simple filter model based on length scales was developed, as well as a more rigorous spectral tensor-based model «
Today, lidars designed for direct wind
turbine integration and control are under development and testing, and one day soon we might see the first wind lidars being integrated directly into the rotating blades.
New IEC standards based on remote sensing? Questions addressed during UpWind WP6 included: “Can remote sensing techniques replace conventional towers with the precision required by the IEC standards?” and “How is it best to exploit the measurement flexibility offered by remote sensing?” Our conclusions from the remote sensing work package were: Using lidars, and without depending on masts, power curve measurements can today be performed on very large wind
International Sustainable Energy Review Volume 5, Issue 3, 2011
power curve measurements. A so-called ‘equivalent wind speed method’ (Wagner et al.2
) was developed to improve power curve
Progress with lidars for wind energy research Turbulence Measurements using LIDARs: At potential wind energy sites, turbulence intensity is also an important quantity to assess in addition to the local wind energy content. Lidar testing during UPWind has shown that, even when the mean wind speed is highly correlated to a reference cup anemometer measurement, the standard deviations in wind speed seen by ground-based wind lidars reveal typically only 60-80 per cent of the corresponding turbulence intensity measured by a mast-mounted cup anemometer. During UpWind we examined lidar
measured turbulence theoretically and experimentally. The cause for the lidar under- estimation results from the large measurement volumes involved with fixed-inclination, azimuth scanning lidars. The effective measurement volume for
lidars typically exceeds 100 meters in horizontal dimension. For comparison, a cup anemometer’s effective measurement scale is only about one meter. To correctly interpret lidar measured turbulence, we found it necessary to account for both the inter-correlations between the wind measurements in different (azimuth) directions and the filtering effects of the radially probing laser beams themselves. A simple filter model based on length scales
A short-range WindScanner (R2D1) during field test at Riso DTU
was developed, as well as a more rigorous spectral tensor-based model. These models were developed to understand and possibly correct for lidar-filtered turbulence. Both models have then been intercompared to turbulence measurements3,4
. We find however, that the ratio
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