While measurements carried out by TNO on the Haliade-X, the world’s biggest wind turbine, are still in full swing on the Maasvlakte near Rotterdam, experts are already working on the next generation of turbines. These will have even bigger blades, produce even more energy and thus reduce costs per kilowatt-hour. All-in-all, an unprecedented technological challenge in which the boundaries of physics are continuously being pushed back.
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The length of turbine blades has already passed the 100-metre mark and we are now heading towards 120, and more,” says Peter Eecen of the wind energy research group at TNO Energy Transition. “But you cannot simply produce bigger blades and then install them, because the forces are inconceivably large at that scale. Every additional metre requires in-depth research and advanced calculations.”
In the four-year STRETCH programme, funded by the Netherlands Enterprise Agency (RVO), TNO is working closely with General Electric (GE) Renewable Energy. The latter is also the owner of the Haliade-X, as well as its subsidiary LM Wind Power, which has an extensive test facility in Wieringermeer, where experiments on wind turbine blades are carried out. The parties have been collaborating for some time in research projects to overcome aerodynamic barriers and thus facilitate the use of ever-larger turbines. In the near future, this will involve further extending the diameter of rotor blades to around 230-240 metres. In the case of the Haliade-X this is currently 220. In terms of aerodynamics, this will entail entering the equivalent of uncharted waters. The research will reveal how the aerodynamic forces on these long blades lead to the resulting loads on the rotor hub and the blades themselves.
“You cannot just make the turbine blades bigger because they will be far too heavy or too expensive”
In the context of the STRETCH programme, experts are exploring the possibility of further lengthening the blades and testing the rotor hub to which the three blades are attached. “The design of the Haliade-X was a huge step in itself, but in this project we will be pushing the boundaries even further,” says Eecen. “But you cannot just make the turbine blades bigger. If you do they will become far too heavy or too expensive, making them an unviable proposition for wind farm manufacturers and constructors. The trick is to come up with an innovative and cost-effective design that strikes the ideal balance between limited loads on the structure and high yield. If we are successful we can reduce the cost per kilowatt-hour of wind energy. This will make offshore energy an increasingly attractive economic prospect, which, in turn, will help to accelerate the energy transition.”
Complex technical puzzle
The higher yield from this new generation of wind turbines will be achieved, not so much through the use of new materials in the manufacture of the longer blades, for example, but through the application of add-ons. Smart add-ons to the blade will improve the flow of wind around it and thus increase yield. It is a complex technical puzzle for which no models are yet available. Measurements and experiments carried out in the test facility will provide valuable data to create new models and manufacturers will then be able to use these to improve their designs. TNO, as an independent scientific party, is validating the measurements and the aerodynamic models.
“It’s not so much about the use of new materials as the application of add-ons”
Full-scale test rig
The test rig that GE and LM Wind Power are building in the Wieringermeer facility comprises the rotor hub of a full-size wind turbine, the rotating central part at the front of the turbine to which the blades are attached. The rotor is subjected to heavy mechanical loads and TNO experts are verifying the strength of the construction. By taking the relevant measurements, the behaviour of the rotor, including the blades and attachments, can be determined.
Given their huge size, this new generation of wind turbines is almost exclusively intended for installation in offshore wind farms. “The tests, experiments and calculations that we have planned should result in turbines that must be incorporated in offshore wind farms in a few years’ time,” concludes Eecen. “Starting next year, tenders are planned for enormous wind farms, such as Hollandse Kust (West), Ten Noorden van de Waddeneilanden and IJmuiden Ver. Our ambition for this project is to have these huge turbines operating in the sea in about five years’ time.”
“Our ambition is to have these huge turbines operating in the sea in about five years”
Leading the way
TNO leads the way when it comes to knowledge of wind and associated aerodynamics, sensors, models and measuring instruments. Leading wind turbine manufacturers use the knowledge and models developed by TNO in their designs. Validation measurements carried out by TNO on the Haliade-X should result in the certification of the wind turbine, after which it will be ready for large-scale production and installation in offshore wind farms. This procedure will also be applied to the next generation of wind turbines on which TNO is working in the STRETCH programme.