Coming with the wind, innovating together to make offshore wind farming smarter

Text by Marcel Burger, corporate reporter, Shell Netherlands

It’s a sunny day at the beach of Egmond aan Zee. The sand seems to dance in the dunes, in an eternal tango with marram grass. A cacophony of screams overhead signals yet another bunch of seagulls flying by, “floating” on the wind from sea.

Beyond the waves hitting the beach, 18.5 kilometres of the coast, “a different concept” is in the making, says Maria Kalogera, CrossWind’s Innovations Manager. The joint venture of Shell and Eneco and partners is constructing an offshore windfarm: Hollandse Kust Noord. “We are finding new ways to make offshore wind production more reliable, for example by adding floating solar panels. We want to prove we can provide a steady stream of electricity flowing to shore, independent of wind force or direction, and manageable per day, hour, minute and second.”

Hollandse Kust Noord will have 69 wind turbines, in a sea depth of 15 to 28 metres and towering 222.5 metres above the waves, including the 97-metre-long blades. These 980-tonne giants producing 11 MW each are impressive, but the real deal will be found around them: innovative solutions to help the whole of the Netherlands.

“This is part of our commitment to Dutch society,” Kalogera says. “Our project will contain new, innovative solutions in producing electricity at sea. We will be transparent; we will share what we learn and our outcomes, to help technological development forward.”

Plan of four parts
This is the plan. Firstly, the wind turbines will be more “intelligent” than before. New software will allow the rotors to make micro-adjustments in seconds, thereby continuously optimizing production under constantly changing wind conditions. This part of the plan is done together with Siemens Gamesa. Secondly, in cooperation with the Technical University of Delft the limiting factor of the so-called “wake effect” is being addressed. This is a form of turbulence similar to what sailing yachts experience when cruising close to another, causing wind instability in the air behind the sail of each ship. For wind turbines this wake effect means less production. Thirdly, to give a more constant flow to the power grid, floating solar panels will be added, for which TNO (the Netherlands Organisation for Applied Scientific Research) is connected to the CrossWind joint venture. Fourthly, various kinds of battery and hydrogen storage of electricity will be tested. The storage is meant to hold “overproduction” that cannot immediately be transferred to the grid, and to make sure there is a stable flow of power even on wind free or sunless days.

Copy and expand
“Our common vision is to keep risk of instability in energy delivery as low as possible, and for that each partner brings its own expertise,” Kalogera says. “With Hollandse Kust Noord we develop an idea into a simple concept. We test it to make the concept a realistic option to copy and expand at future offshore windfarms. We will investigate and optimize. With what we learn we take solid steps in accelerating the energy transition.”

For the Netherlands, there are more challenges. Weather pattern changes and the national plans call for a forced growth of offshore wind to 21 GW by 2030. Solutions are needed to prevent the grid of reaching its limits, CrossWind’s innovation manager says.

“To put it simple: when power supply is more flexible and balanced, it will be able to match demand, reducing the need for additional investments in hardware and system upgrades. As such, we can minimise the overall societal cost to decarbonise the power system.”

Wake effect
One of the leading innovative partners is the Technical University of Delft. Professor Jan-Willem van Wingerden is the expert in the field of data-driven control solutions for wind turbines and farms. “One of the challenges is finding a solution for the “wake effect”. For professional road cyclists this effect is fantastic. In the chase, pursuing cyclists profit from the lead cyclist. He or she keeps them out of the wind and provides them with suction wind stream. However, in wind farms these wakes mean less energy production for the second, third and so on turbine. Moreover, there is turbulence behind a rotor, and with high values this can even limit the lifecycle of a wind turbine.”

To mitigate the wake effect, there are several options. One of them is placing the wind turbines that far apart that they will all face similar situations. The result is fewer turbines per square kilometre and therefore less productivity. “The trick is to find a balance between the economical and the technical possibilities of a wind farm. In other words, how to limit the effects of suction wind and therefore maximize energy production.”

Van Wingerden says that several strategies are possible to reduce the wake effect. The most obvious one is that upstream turbines reduce the strength of their own wake, by limiting the number of rotations of the propellor. But this doesn’t seem to have the desired effect.

The second is called “yaw control” or “wake steering”: the entire rotor is swivelled, so that the wind streams differently alongside the turbines. “But its aerodynamic success depends on accurate knowledge of the entire so-called wind field of the farm and needs to be refined by continuous measuring and adjusting.”

Finding the sweet spot
The flagship solution is to adjust all rotor blades individually, to create a helix wake behind the turbine. To make this theory reality software coding, wind tunnel probing, scale model testing and finally, from 2025, real-life proving at Hollandse Kust Noord is needed to show it works in real life.

“It is about finding the sweet spot for each individual rotor blade and making sure the frequency of the rotations doesn’t hurt the structure. After all, nobody likes to have rotor blades giving in or falling off.”

Sustainable testbed
Meanwhile all work is being done to get CrossWind’s windfarm Hollandse Kust Noord ready to commence production of sustainable electricity from wind by 2023. The five innovations will be added in 2025.

For those taking a stroll at the beach of Egmond aan Zee not much will change. The wind will blow the way it does, the sand will be displaced, the marram grass will wave like any other day and the seagulls will keep “floating” in mid-air. But looking out over the sea, on a clear day you might just see the contours of a very special testbed at work.

Source: Venster Magazine
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