Offshore wind energy has an important part to play in the Dutch Government's plans to meet the targets outlined in the Paris Agreement. The HKN wind farm is expected to produce energy for some 1 million households by the end of 2023. The project will also serve as an example to other offshore wind farms, helping to make wind energy more efficient and, therefore, also cheaper in the future.
Existing wind farm flow control algorithms, primarily through wake steering, are based on steady-state engineering models that neglect the dynamics of the wind farm. This results in sub-optimal power output at the wind farm level. Flow or wake control, coordinated by a wind farm controller, will result in a higher energy yield for the wind farm.
A wind turbine produces electricity from the kinetic energy present in the wind blowing on it. As the turbine extracts energy from the wind, it reduces its speed. A region of low velocity called a wake, is therefore formed downstream of a wind turbine. In a wind farm, where turbines are placed relatively close to each other, downstream turbines often operate in the wake of upstream ones. This means they operate in zones of lower wind speed and, therefore, produce less. This is known as the wake effect and generates power losses between 10% and 20% on Annual Energy Production at the scale of wind farms.
Limiting those losses requires a paradigm shift when it comes to wind turbine control. Currently, wind turbines operate greedily: they all try to maximize their individual power production. But this is not the optimal strategy in a wind farm context, as turbines interact through their wakes. Control strategies should, therefore, be developed with a collaborative approach: wind turbines should become team players.
Wind farm flow control algorithms are investigated, as they will result in a higher energy yield for the wind farm. There are currently two main approaches to do so: either deviate wakes from downstream turbines or make sure wakes become weaker by making them recover faster. The first approach is known as wake steering and is done by willingly misaligning the turbine from the incoming flow. The second approach is called wake mixing and the HELIX control is one of the promising wake mixing strategies. It helps the wake recover faster by forcing is to propagate as a helix.
The innovation project ‘Dynamic Wind Farm Flow Control’ contributes to the effort of minimising wake effects for modern wind farms. The main goal is to mature and demonstrate wake mixing and wake steering strategies at the offshore wind farm Hollandse Kust Noord (HKN). The project wants to demonstrate that the energy yield of wind farms will increase by including the dynamic flow control and to bring those strategies from TRL3 to TRL7. One of the challenges will be deploy those strategies in uncontrolled, time-varying and turbulent wind conditions.
The HELIX technology will first be explored in more depth using both numerical and experimental studies. The numerical work relies on high-fidelity computational fluid dynamics tools to provide detailed wake and loads analyses. These numerical results will then be compared with experimental results from wind tunnel experiments. The HELIX technology will then be deployed onshore at a research test site. Once numerical work, experimental lab tests and experimental onshore field tests are completed, the HELIX technology will eventually be implemented at one of the SG 11.0-200 DD wind turbines at the HKN wind farm.
In parallel to wake mixing, wake steering is also investigated in this project. Existing wake steering algorithms for wind farms are currently based on steady-state engineering models that neglect the dynamics of the wind farm. This results in sub-optimal power output at the wind farm level. To avoid this limitation, closed-loop wake steering is further developed in this
project and will also be demonstrated at HKN.
The final phase of the project focuses on the potential impact when these control technologies are rolled out across the full wind farm and how these control technologies can impact the design and power production of future wind farms.
The project has several phases, which include computational studies, wind tunnel experiments and onshore field experiments. The technologies will eventually be demonstrated offshore on one of the Siemens Gamesa 11.0-200 DD wind turbines at the HKN wind farm. Finally, the potential impact of the full roll-out of these technologies across the entire wind farm is researched, as well as how these technologies could impact the design and power production of future wind farms.
Jan-Willem van Wingerden is pleased to be involved with the HKN project. “Collaboration with the industry shows how we are directly impacting society. The results of our research will immediately be tested on a large scale and refined where necessary."
In this project, we will unleash the true potential of the novel HELIX active wake mixing concept by detailed experiments and field tests while the closed-loop wind farm control technology is further matured. The technology maturation and validation at farm scale are of crucial importance for the wide adoption of dynamic flow control concepts by wind farm developers and operators. It has the potential to further drive down the levelized cost of electricity (LCOE) of wind and improve the controllability of the flow.
The project team expects the project to result in three major improvements: