Wooden wind turbines to reduce vibrations
Vibrations from wind turbines could disrupt the measurements of the Einstein Telescope. At present, a safe turbine-free zone of 10 kilometres around the telescope is assumed, but using wooden masts instead of concrete could reduce vibrations caused by wind turbines. Achim Stahl, director of the Institute of Physics at RWTH Aachen University, is optimistic after initial research. Austrian company Hasslacher Green Tower is working on a prototype.
Most wind turbines are constructed from a concrete and steel mast and stand on a concrete foundation. When the rotor blades turn, vibrations are created that would reach the Einstein Telescope, 250 metres underground. “Research shows that interference is possible if they are within approximately 10 kilometres,” says Achim Stahl. “So the safest thing would be to maintain that 10-kilometre margin. However, this is a sensitive issue politically, and we fully understand that wind energy is an option in this region as well.”
Advantages of wood
There is currently a buffer zone of about 10 kilometres. Research is being done to determine whether a much smaller buffer zone or perhaps even no wind turbine-free zone at all will be needed in the vicinity of the telescope in the future. “We know that wood transmits vibrations much less than metal and concrete. A wooden mast could therefore be one of the solutions. Wood is also lighter, which means that foundations can be different, and it is more sustainable than steel and concrete. All of these are additional advantages.”
Through another research project at RWTH in Aachen, Achim Stahl came into contact with Austrian company Hasslacher Green Tower, world leader in glued laminated timber (Glulam) beams for wooden construction in bridges, houses, offices and apartment buildings, among other things. “Hasslacher has been working on an alternative to concrete and steel in wind turbines for some time now. In fact, various options are already at an advanced stage. We have entered into discussions and are now investigating whether a wooden construction does indeed result in fewer vibrations in the soil. The first evaluations, partly based on simulations, are optimistic.”
Extensive experience
Hasslacher Green Tower Product Engineer Carlo Schröder explains: “It’s true that we’ve been working on an alternative to concrete wind turbine masts for a number of years. Two designs have already been completed and approved by the TÜV inspection authority. Together with RWTH, we’re now working on a third digital prototype, specifically for installations over 160 metres tall. Technically speaking, it isn’t that complicated. We have a lot of experience with all kinds of applications of wood in building structures. We certainly think it’s a suitable material for wind turbines, which we see as a new market with potential. That’s why we’re also happy to work with RWTH. We’re learning more about the sustainable aspects and about damping vibrations. And of course, it would be fantastic if we could contribute to the construction of the Einstein Telescope near Aachen.”
Four frames
Carlo Schröder shares figures and a series of images of the prototype, including an animation of a wind turbine in the landscape. This is a structure of four tapered wooden frames (just like in old half-timbered houses) topped by a steel tube. The three rotor blades are connected to the nacelle on top of the tube. “A total of 200 metres high if you include the blades. Ninety percent of the construction is wood, including the hollow shaft in the centre with space for all the cables and the maintenance lift. We are now well-advanced in the virtual test phase. This construction is solid and can absolutely compete with the existing concrete and steel wind turbines. The only difference is that the wooden one is lighter and can stand on a different foundation, on four points, with less concrete.”
After extensive research, Achim Stahl knows that the foundations are particularly relevant for the vibrations. “We don’t have exact figures yet; we want to be able to test in practice later. However, the simulations are promising. I really do think that the wind turbine-free zone around the Einstein Telescope could be much smaller in the future.”
Carlo Schröder nods in agreement, but does not venture any figures. “We know more about wood and what you can do with it. You can build the towers with wood from specially cultivated forests. Sustainable, in other words. The new type of wind turbine requires approximately 400 to 500 500 cubic metres of that wood. That also means 400 to 500 tonnes of CO2 absorption. Furthermore, wood lasts a very long time. The tower for the wind turbine can withstand the certified loads for the lifetime of the turbine, usually 20 years or more. After that, the wood can be reused and the tower makes its contribution to decarbonisation.”
Social impact
Compare that with the use of concrete and steel, adds Achim Stahl. “The production of these materials is energy-intensive and far from circular. Of course, our primary interest in this research is the Einstein Telescope, but there is more. Sustainability, including lower CO2 emissions, and other applications. Current generations of wind turbines also interfere with other seismological measurements, such as those of possible earthquakes. The social impact is therefore much greater than just that beautiful telescope.”
Hasslacher is in talks with European and Chinese wind turbine manufacturers about the possibilities of wooden structures. “The challenge is to get the cost price below that of the current models,” says Carlo Schröder. “That should be possible, especially since the wooden structures are easier to install on slopes and other difficult places. That’s a long way off. First, we want to build a prototype before summer next year that will give us a definitive answer about vibrations.” And the Einstein Telescope may then be able to cross another question off its list.
