First in situ evidence of wakes in the far field behind offshore wind farms

TLDR

More than 12 GW of offshore turbines are operating in Europe, where farms are clustered in hundreds of units; while wakes are usually local, satellite imagery shows they can extend tens of kilometres under stable stratification. The study aims to understand wind‑farm wakes to optimise layouts and operations and reduce costs. Researchers conducted the first direct in‑situ measurements of large offshore wakes with a specially equipped research aircraft in 2016–2017, forming part of a larger project that also analysed satellite imagery and numerical models. The aircraft measurements confirmed that stable‑atmosphere wakes can exceed tens of kilometres, with wind‑speed deficits up to 40 % and increased turbulence.

Abstract

More than 12 GW of offshore wind turbines are currently in operation in European waters. To optimise the use of the marine areas, wind farms are typically clustered in units of several hundred turbines. Understanding wakes of wind farms, which is the region of momentum and energy deficit downwind, is important for optimising the wind farm layouts and operation to minimize costs. While in most weather situations (unstable atmospheric stratification), the wakes of wind turbines are only a local effect within the wind farm, satellite imagery reveals wind-farm wakes to be several tens of kilometres in length under certain conditions (stable atmospheric stratification), which is also predicted by numerical models. The first direct in situ measurements of the existence and shape of large wind farm wakes by a specially equipped research aircraft in 2016 and 2017 confirm wake lengths of more than tens of kilometres under stable atmospheric conditions, with maximum wind speed deficits of 40%, and enhanced turbulence. These measurements were the first step in a large research project to describe and understand the physics of large offshore wakes using direct measurements, together with the assessment of satellite imagery and models.