Minimising wake effects for wind farms by closed-loop active wake steering and novel active wake mixing technology


The innovation project ‘Dynamic Wind Farm Flow Control’ aims to take the crucial next step in the effort to minimise wake effects for modern wind farms. To do so, the partners develop the novel active wake mixing technology called the HELIX and work on the implementation of closed-loop wake steering. In this project, the main goal is to mature these technologies and demonstrate them at the offshore wind farm Hollandse Kust Noord in time-varying atmospheric conditions.

   

These active control strategies can lead to::

  • Increased annual wind farm power output by: 2 to 3%.
  • More stable power output with decreased dependence on apparent wind speed.
  • Reduced offshore space use thanks to reduced turbine spacing.
“A wake is created behind each turbine, and considerably less energy can be generated in this wake," explains Jan-Willem van Wingerden, Professor at TU Delft. “Our techniques can be used to make the so-called wakes shorter or change their direction so that more energy can be generated by the turbines and the predictability of energy production can be improved. The HKN project is now offering us the opportunity to test these methods in practice and optimise them."

Wind turbines in large wind farms could produce more energy than they currently do. This is due to the wake, an area of low wind speed behind a turbine. If this wake interacts with another turbine, it can lead to a reduced electricity production of up to 25% for the affected turbine. This project investigates technologies to reduce the effect of these wakes by focusing mostly on two kinds of strategies.

First, we consider active control of the turbine blades. The blades can be pitched, which means that they can rotate around their spanwise axis to change their orientation towards the wind. When the blades are continuously pitching, the wake behind the turbine is disrupted. The low-energy wind from the wake mixes with the high-energy wind from outside the wake. This is called wake mixing. Two blade pitching techniques are becoming popular:

  • The PULSE, for which the three blades of the turbine are periodically pitched with the same angle, resulting in a pulsating effect in the wake.
  • The HELIX, which is the main focus of this project, for which each blade is pitched individually, forcing the wake to propagate as a helix.

Second, we work on control of the turbine orientation towards the wind. The wind turbine can
be misaligned with the wind so that its wake is deviated from downstream turbines. This is
called wake steering and it introduces a new degree of freedom in wind farms. This calls for
the development of new approaches for both wind farm design and operation. With this project,
we look at the operation part by developing closed-loop active wake steering. The goal is to
consider the dynamical changes in wind conditions to reduce wake interaction and limit power
losses.

The Hollandse Kust Noord wind farm

CrossWind, a joint venture between Shell and Eneco, develops and will operate the Hollandse Kust Noord subsidy-free offshore wind project. Together with TU Delft and its partners, CrossWind is looking at ways of using real-time data to reduce the wake effect across the entire wind farm.

GROW

The Dynamic Wind Farm Flow Control project is part of a joint research programme in offshore wind called GROW. This consortium initiates research and accelerates innovations. GROW’s strength lies in its ability to run focused, sequential, complementary RD&D activities. The consortium includes over 20 leading and committed partners cooperating closely to conduct joint research.