Abstract
Wind and power deficit in the wake are assessed for the offshore wind farm Alpha Ventus. Operational data are evaluated for the power deficit in the wake of a single wind turbine and in a row of wind turbines. The wake of a single wind turbine is described by the maximum power deficit and expansion width of the wake. The impact of atmospheric stability in respect to vertical wind shear and turbulence intensity is assessed showing that wake effects are more pronounced under stable conditions.
Highlights
Stability classification according to the wind shear and turbulence intensity
21-24% at the 2nd wind turbine and about 1% more at the 3rd wt in a row. These results are in broad agreement with the results documented for Horns Rev, which has a similar spacing of 7D
For a smaller wind direction sector of ±2.5° the power deficit at the 2nd wt is about 43-50%, which is higher than the respective power deficit observed in Horns Rev of about 35% [2]
Summary
Stability classification according to the wind shear and turbulence intensity. Chosen limits are shown in the figures as green lines. 6/2012 (wind data) have been assessed for wake effects. The power reduction along the row with a spacing of 7.3D has been assessed for wind speeds of 8-10m/s. At a larger distance the rotational motion is depleted by friction; the wake propagates in line with the wind direction again. Sommer: Power deficits due to wind turbine wakes at Horns Rev wind farm, Torque. Neumann: CFD simulations and measurements of wake effects at the Alpha Ventus offshore wind farm, EOW 2011, Amsterdam. Cañadillas: Influence of atmospheric stability on wind turbines (WT) power performance at Alpha Ventus offshore wind park, EOW 2011, Amsterdam v=[7;11m/s], dir=270°, unstable. Left: Power deficit of the AV5 for v=[7,11ms] for different stability conditions in respect to wind shear and turbulence intensity. 0.3 all data α0.15 (stable) unstable - stable (pow(unstable) - pow (stable)) /pow(all) [%]
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