Annual impact of wind-farm gravity waves on the Belgian–Dutch offshore wind-farm cluster

Dries Allaerts,Nicole Van Lipzig,Johan Meyers,Sam Vanden Broucke

doi:10.1088/1742-6596/1037/7/072006

Abstract

While research on wind-farm–atmospheric boundary layer interaction has primarily focused on local effects inside and above the farm, recent studies found that wind farms may affect the wind conditions several kilometres upstream of the farm via the excitation of atmospheric gravity waves. Such non-local effects can have strong implications for the windfarm energy extraction but are currently overlooked in wind-farm design and operation and control strategies. In the present study, we employ a fast wind-farm boundary-layer model in combination with ERA5 reanalysis data to assess the potential impact of wind-farm induced gravity waves on the annual energy production of the Belgian–Dutch offshore wind-farm cluster in the North Sea. We estimate the annual energy loss due to the effect of self-induced gravity waves to be of the order of 4 to 6 %.

Highlights

Over the past years, research on the interaction between wind farms and the atmospheric boundary layer has primarily focused on local effects related to the complex interaction of multiple turbine wakes and the associated slow down of the atmosphere inside and above the farm; see Ref. [1] for a review
We find some cases with a negative velocity reduction, indicating that the wind is accelerating in front of the farm
We relied on a fast windfarm boundary-layer model that was designed for the specific purpose of investigating gravity wave feedback effects

Summary

Introduction

Research on the interaction between wind farms and the atmospheric boundary layer has primarily focused on local effects related to the complex interaction of multiple turbine wakes and the associated slow down of the atmosphere inside and above the farm; see Ref. [1] for a review. Recent large-eddy simulation (LES) studies showed that the upward flow displacement in response to the collective flow blockage in large wind farms may excite atmospheric gravity waves on overlying inversion layers and in the free atmosphere [2, 3, 4]. These gravity waves impose significant pressure gradients in the boundary layer and may lead to modified wind conditions several kilometres upstream of the farm.

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Conclusion