Amsterdam-based TouchWind is developing a completely new design for a floating wind turbine. This turbine uses a one-piece rotor placed at an angle to the wind. The innovative design reduces the cost of the turbine without compromising the yield. In addition, maintenance is easier and turbines can be placed closer together in a wind farm, said TouchWind's general manager and co-founder Mark Goossens.
Top Sector Energy entered the discussion
What problem have you found a solution for?
"The current generation of wind turbines have a rotor with pitch control on each blade. This controls the rotor speed to maximise energy yield. To avoid overloading the generator, the turbine is switched off at wind speeds above 25 m/s. Pitch control is a costly and complex system with many components. In addition, traditional rotors tend to destabilise the floating structure. To ensure stability, you need huge floats, resulting in a high LCoE."
What is at the heart of your solution?
"Our rotor consists of one structural part and is angled to the wind: the higher the wind speed, the more horizontal the rotor and therefore, the smaller the projected rotor surface. This is how we control the rotor speed. Constructively speaking, this is a lot less complex, but it raises new problems. Because how do you prevent the rotor from breaking because of the asymmetric load on the rotor shaft? We managed to solve that mechanically by connecting the rotor to the shaft in a clever way.
The rotor is designed to generate large vortices. Normally, the low-energy wake of a rotor strongly influences other wind turbines downwind. With our rotor design, the rotor surface vortices behind the rotor mix the low-energy and energy-rich air. In doing so, we actually use more air: even air that does not flow through the surface of the rotor.
We have increased the stability of the wind turbine by turning the rotor a quarter turn. This makes it almost perpendicular (± 80⁰) to the mast. Regardless of the wind direction, the rotor always pulls in the longitudinal direction of the mast, stabilising itself. The harder the wind, the harder the rotor pulls the turbine up, stabilising the system."
What is so groundbreaking about your innovation?
"The complete principle is unique. If you put a rotor at an angle to the wind, you would expect it to catch less wind and thus reduce energy output. According to Betz's law, this is true because the flowing rotor area becomes smaller. However, we managed to tilt the rotor without compromising yield: in fact, we use large vortices. Moreover, the stabilisation method is groundbreaking. The rotor is (more or less) perpendicular to the mast and pulls upwards. So as long as you make sure the system does not 'fly' out of the water, the rotor stabilises the floating system."
What does your system deliver?
"Our wind turbine is cost-efficient because the construction is relatively simple. The rotor consists of one part; no pitch control per wing is required. Aerodynamically it is very complex, but structurally quite straightforward. Maintenance costs are low because there are fewer components and the turbine can be tilted to the water surface. Moreover, our turbines can be placed closer together. They can be placed an estimated 1.5 to 2 times closer together (compared to conventional turbines). This applies In two directions and thus results in a quadratic growth of turbines per square kilometre. Moreover, at higher wind speeds, they can just keep on turning. So our wind turbine not only generates more electricity, but also more often. And finally, the turbine can be mounted in port. This makes offshore installation much easier and therefore reduces CAPEX. "
What challenges do you face?
"It is a completely new technology that has to be designed integrally. All aspects influence each other, so the hydrodynamic and aerodynamic behaviour will have to be calculated in one mathematical model. In addition, it involves large investments. We are working with major partners, but we are a new and relatively small player. The (floating) offshore wind market is characterised by a limited number of dominant players with huge interests. So besides the technology, our challenge is: how do you successfully bring a completely new technology to the market?"
Where are you now?
"We have formed a consortium with two knowledge institutions (TU Delft and Marin) and three industrial parties (VDL, Nidec and We4ce). The consortium received a grant from RVO so that we can continue working on the design for the next three years. We simulated the dynamic behaviour of the system and tested research models in the wind tunnel. The measurements largely confirm our theories on vortices and energy production. The wind turbine rotates stably in an inclined position and produces more energy in this position than in vertical (conventional) position.
What are your next steps?
"The research models have a rotor diameter of 1.20 metres. That is the maximum for this wind tunnel. Therefore, we want to test the next 6-metre model outside. In 2022, we will test some models with a diameter of ± 30 metres, focusing on the effects of wind farms. We already know that they can be placed closer together than traditional turbines, and we want to investigate how close together that can be for maximum energy yield."
What do you gain from Offshore Wind Innovators and TKI Offshore Wind?
"Without Offshore Wind Innovators, it would have been much more difficult to form this consortium. Their network helped us gain knowledge about the market. Innovation manager Martin Weissmann brings parties together and he does a fantastic job. In addition, we can spar well on the right strategy. TKI Wind at Sea's network meetings are also a very pleasant way to get in touch with other parties."
Source: Top Sector Energy ism Offshore Wind Innovators
