Mees van Vondelen (28) absolutely never wanted to do a PhD. “I wanted to go into business. I thought studying was fine in itself, but it was more of a necessity.” PhD students sat alone behind a laptop all day and were not very social, he thought. Nothing for him.
Van Vondelen is in the lab at TU Delft where he conducted a large part of his PhD research. It died out just before the Christmas holidays. Only two employees are in their office. All walls are made of glass. In addition to the large room with all kinds of test setups – a crane, car seat with steering wheel and a man-sized windmill – there is a smaller glass room. It contains the ‘wind tunnel’: ten interconnected scaffolds that most closely resemble stage parts measuring half a meter wide by two meters high, but with glass walls and ceiling. It contains three mini wind turbines, half a meter high.
Here, Van Vondelen designed an algorithm to make wind turbines “surf along with the predecessor like birds – but the opposite: with more resistance. Now it’s every turbine for itself.”
It was big news recently: wind turbines keep each other out of the wind and produce less energy than expected. This was evident from research by, among others, TU Delft. The Netherlands may have expected too high a return. “It was presented as breaking newsthat mistakes have been made,” says Van Vondelen. “But that has been known for a long time. Ever since wind farms were built, we have known that they can get in each other’s way. That is a given.” It seems unlikely to him that “such a basic mistake was made.” “Ultimately it is up to industry and science to come up with solutions for this. And that is what we are also doing.”
The problem with wind turbines is that the front turbines steal the wind from the rest. This makes them 10 to 20 percent less efficient, says Van Vondelen. “A significant number.” This so-called wake effect can be as long as fifteen rotor diameters – 3.5 kilometers for the largest turbines at sea – depending on the circumstances. Various solutions have been devised, says Van Vondelen, but all “very static”. Let the front turbine spin a little softer, for example. But that appears to have little effect on the production of the turbine behind it.
Dozens of whirring fans
The TU Delft research group came up with something different – even before Van Vondelen was involved, by the way. They rotated the blades in a certain way on their axis, so that the air behind them formed a spiral. “A kind of spiral. We call it the helix.” And then something funny happens, says Van Vondelen: the fast-flowing air around the helix is drawn in, causing the average wind speed to increase. The production of the entire park increases. TU Delft patented this invention, which has not yet been tested in real wind turbines.
Van Vondelen can demonstrate it. He starts up the computer that is directly outside the wind room, looking straight into it. But the desktop cannot connect to the wind computer. Van Vondelen tries different buttons and websites and then asks the lab staff for help. They mess with wires, ports and IP addresses.
“Ah, the cable wasn’t in yet!” Van Vondelen: “We are live.” He turns on the wind. Dozens of small computer fans on the right side of the tunnel begin to hum. The rear of the three small wind turbines starts turning. “It is already at the right angle, I am now adjusting the other leaves.”
Lines in graphs start to rise on the screen. “The pink one is the rear turbine. The blue one is the second one, the red one is the front one. And the dark blue one is all added together. So you can already see that the front one produces a lot of energy.” The red line climbs much higher than the other two. “That is a bizarre difference. They are now exactly in line full wake overlap. This is the worst-case scenario.”
Testing in an offshore wind farm
Time to turn on the invention. Van Vondelen tinkers with some values in the program: “It would be fantastic if it worked in one go.” “The frequency comes in, now you see that the blades start to vibrate.” We are sitting right next to the front windmill. The side view of the rotating blades is distorted. The production line of the front mill dips slightly on the screen. But the other two are climbing, as is total production.
After his bachelor’s degree in mechanical engineering, Van Vondelen did his master’s degree systems & controlalso at TU Delft. He did his graduation assignment at Siemens Gamesa, which builds wind turbines. “That was the first time that I was able to apply the theoretical knowledge from my master’s degree to an industrial problem. It produced results that were actually useful for the company: I really enjoyed experiencing that.” Halfway through that assignment, his supervising professor suddenly asked if he wanted to pursue a PhD in the same research. “I was very shocked.” Him, a PhD?
The university set up a new research project with three large wind energy companies, which will ultimately be tested in the new Hollandse Kust Noord wind farm. The longer he thought about it, the more Van Vondelen liked it more and more. The end result would be tested in a real wind farm, he could collaborate a lot. “So yes, that’s when I started doing it. It is a unique opportunity: I think there are few scientists who can test their idea on such a scale.”
His research question: whether the helix concept also works on the second turbine in the row. This is a lot more complicated than with the first turbine, because the air already enters in a spiral form, Van Vondelen explains. “You can see it as a resonance: if it has a certain phase difference, it amplifies each other. So that is quite an interesting process. Because it turns out: if it amplifies each other, it actually means that the wind speed behind it becomes even higher.”
Patented invention
He devised an algorithm that can construct exactly the phase of the incoming wind – the wake – based on the vibrations of the blades. And the turbine then adapts itself accordingly. Van Vondelen did endless simulations and tests, with “all very positive results.” This invention was also patented. With this technique you could even build the wind turbines closer together, says Van Vondelen. And his algorithm is especially interesting when there is little wind: that is when it works best and the electricity price is high. Above 10 to 12 meters per second, wind force 5 to 6, it adds nothing: then all turbines will deliver enough anyway.
More research is not necessary for the next turbines in the line. “The problem mainly occurs when you have very laminar wind; with little turbulence. This is mainly at sea, because there are few obstacles. Then the wake is also very long. On land you have more turbulence, the air is already mixed due to trees, mountains or buildings. In a wind farm you actually have the same thing: as soon as it passes the second turbine, you see that it doesn’t actually add much anymore, then you already have inherent mixing.”
And there are also disadvantages. “By continuously moving the blades you create more vibrations. And you want to avoid vibrations: this causes turbines to wear out faster.” How much faster depends on the situation. “But you can do serious damage if you don’t take it into account.” That is where the biggest challenge lies, says Van Vondelen: keeping the vibrations under control. The entire turbine would have to be optimized for it. “If you subsequently allow a turbine to do something other than what it was designed for, that is always a bad idea.”
Looking back, he really enjoyed doing research: “It was great fun to be able to fully immerse myself in something for four years. The autonomy and freedom you have to give your research your own direction was really great. And I was lucky that I had very nice colleagues.” A PhD: he can recommend it to everyone.
Who is
Mees van Vondelen?
- Born
- in 1997.
- Born in
- Zeist, recently moved from Rotterdam to Amsterdam.
- Hobbies
- Skiing, diving, cycling.
- Finds wind energy:
- “An interesting problem. Not everyone in this field is one tree huggeror someone who will never fly again. The fact that it is good for the world is a bonus.”
- Works now:
- At a patent office. “People come up with an invention that I have to fully understand and record legally. I came into contact with that when we were going to patent this invention. After my PhD, I decided for myself: what do I like? A strong point of mine is that I can deal well with people. And I love technical innovation – this profession encompasses all of that.”
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