In Skara, the world's tallest wooden wind turbine tower is currently being erected. Modvion is building the unique wooden structure that reaches a height of 105 metres. Why do you want to replace the commonly used steel with wood?
In 2020, the country's 4333 wind turbines produced 16% of our energy in Sweden (Energi myndigheten 2020, Ny statistik över installerad vindkraft 2020 (energimyndigheten.se). That's a lot of power plants and more are expected in the coming years. They produce renewable energy, but also contribute to greenhouse gas emissions. In general, today's wind turbines are built with materials such as steel and concrete. Strong materials that can withstand the forces a wind turbine is subjected to, but the traditional choice of materials contributes to high greenhouse gas emissions. The largest contributor to the climate impact of wind power comes from the raw materials used in the manufacture of the turbines.
The wind power industry has a need to reduce the climate impact when manufacturing new power plants. The Gothenburg-based company Modvion is helping to reduce the climate impact of the wind power industry by replacing the tower, which is usually made of steel, with a wooden tower of the same height. In 2020, the first 30-metre-high wooden wind power tower was erected on Björkö in the Gothenburg archipelago. Another tower was recently erected in Skara, reaching 105 metres. Subsequently, even higher towers are planned to support turbines with even greater production capacity.
Advantages of wooden wind towers
Wood is a renewable material that also sequesters carbon over the life of the wind turbine. Steel is strong - stronger than wood - but it is also heavy. When comparing the strength of materials in relation to their weight, wood outperforms steel. In increasingly tall towers, the weight of the tower means that the steel tower needs to be reinforced to support its own weight. Wooden towers, which are lighter, do not have the same problem with their own weight and so it is possible to build tall and slender with wood. To cope with the extreme forces of the massive rotor blades at the top of the tower and the strong winds to which a wind turbine is exposed, Modvion has developed and now manufactures wooden frames for wind towers. The construction consists of thin wood laminates that are glued and pressed together into curved 15 metre long wooden modules. The modules are erected, joined and then stacked on top of each other to erect the tower. The relatively small size of the modules allows them to be transported to the construction site by smaller lorries compared to today's steel towers where specialised vehicles are used to transport larger components.
Development work
One challenge has been to develop strong joints for joining the modules that can be efficiently assembled on site and withstand the extreme forces on the tower. The solution used is inspired by a relatively new technique where a steel plate with holes is glued between the wooden elements to be joined. This differs from traditional jointing solutions where steel plates are used in combination with, for example, screws, bolts or dowels. Using glue instead of metal connectors results in very strong and rigid joints. The manufacture of glued wood structures is usually done in a factory in a controlled environment and under controlled conditions. On the construction site, temperature, humidity and working conditions vary and thus it can be difficult to control the quality of the gluing. In the project Stuck in the middle with you (SIMWY), funded by Vinnova, Modvion, Henkel and RISE are collaborating to develop Modvion's method for construction gluing on the construction site. You can read more about the project on the project website, (Link).
Developing new technology means that it needs to be tested and evaluated. RISE has experts in various subject areas and laboratories for testing and evaluating materials and structures, both on a small and large scale. Together with Modvion, RISE has tested the the new hybrid joint for different types of loads that mimic those it needs to withstand in reality in a completed wind turbine tower. The joint has also been subjected to fatigue through cyclic tests where it has been loaded and unloaded thousands of times over a long period of time to failure. Fatigue is rarely relevant in ordinary wooden buildings, but in structures such as bridges and nowadays tall towers that are loaded with high varying loads during their lifetime, the phenomenon becomes relevant.
This is an article from our magazine Trävärden, it is available in full here! (Link)
