Wake behind an offshore wind farm observed with dual-Doppler radars

Abstract

We present dual-Doppler measurements of the wake behind an offshore wind farm. The measured wind speed in the wake is compared with two wake models, one resolving the single wakes from individual turbines, the other describing the wind farm as a distributed area of increased roughness. We analyse a case with steady wind direction approximately aligned with the turbine rows. The radar measurements allow us to track the evolution of the wakes through the wind farm and further downstream. In the case studied here the wake region extends at least 17 km downstream of the wind farm. Both models are in good agreement with observations provided a coastal gradient is accounted for. The generality of this conclusion is tested by comparing modelled wind speeds with observations aggregated over multiple cases with a similar inflow wind direction.