Composite tower for light-weight and low-maintenance wind turbines
Jules Dock has designed a tower made of glass fiber reinforced plastic which is 100 meters high and 40% lighter than steel, making it easier to install. Moreover, the tower requires little maintenance. With this concept, Jules Dock has won the jury prize of the Offshore Wind Innovation Award. A scaled model is currently undergoing all kinds of tests; an automatic production line is the next challenge
Interview with Jelmer de Lange, director of Jules Dock Innovation
For what problem have you found a solution?
"The installation of wind turbines is time-consuming and costly. Now that wind turbines become larger and heavier, the installation companies have to adapt or even replace their transport vessels. The vessels often sail back and forth for all the tower segments which are welded together on site. With a lightweight construction of composite you can make longer use of existing installation vessels. Furthermore, the maintenance costs become more important, especially the regular inspections of welds and bolted joints. Composite constructions consist of one piece and are well resistant to salt and seawater. "
What is the core of your solution?
"We first had the idea of composite monopiles, but composite material is not resistant to the high impact forces of piling. The transition piece and the tower are more suitable. We have chosen for the tower because it is the heaviest; weight saving at the top yields the most.
Together with Knowledge Center WMC, we wrote a project proposal in 2015. With R&D subsidy from TKI Wind op Zee we were able to investigate the feasibility of a 10 MW turbine tower on the North Sea that can generate electricity for 20 years. A 10 MW turbine was the most practical because a lot of data is available.
The first concept, C-Tower, consists of basic composite materials such as glass fiber and resin. We lay woven fiberglass mats together in different directions. After hardening, this laminate is as strong as a steel segment. We calculate the optimum stiffness, strength and vibration frequency per segment. "
What is so groundbreaking to your innovation?
"There are no towers of composite material yet because the weight was not an issue until now. The clever way in which we lay the fibers in a certain direction are groundbreaking. With this we have achieved 40% weight savings, in the next design round we go up to 50%. This percentage is necessary because composite material is about twice as expensive as steel.
Innovative is also the idea to produce the tower as a whole, in a single hall and one per day. "
What are the benefits?
"40% less weight saves about 300 tons on a 10 MW wind turbine. Moreover, the tower is constructed in a single piece. This allows existing ships to take and install an entire tower in one go. That makes the installation faster, easier and cheaper. Maintenance costs are also substantially lower. The towers are less susceptible to corrosion. Inspections can be limited to the connections at the foot and at the top."
What are the challenges?
"A disadvantage of composite material is that it is more difficult to repair on site. In addition, composite material is more flexible, it bends. If that happens too much at the expense of the performance, a stiffer and stronger construction must compensate for that, making the tower heavier again.
In addition, certification is a costly process. There are no guidelines for composite towers yet. Do you assume the guidelines of steel towers or of composite rotor blades? We are in discussion with certification bodies to develop suitable design guidelines.
So far, we finance the project with our own resources and R&D subsidy. We are in discussions with private investors to develop large demonstration models. They see opportunities. "
How far are you now?
''We perform tests with a scale model of 5 meters height (1:20) and a diameter of 1 meter (1:10). In the summer we want to carry out tests with the improved design. Then we will approach market parties. Furthermore, we are busy with the design of the hall and the development of a reliable and accurate production technique. We have now produced one piece that way. "
What are your next steps?
"A demonstration tower. On land, because it is difficult to place a single tower at sea. With this demonstration we want to prove that the production is feasible and the tower meets the requirements. We want to produce it in a year's time, to be positioned late 2019. In 2020, we want to have the hall fitted out and to be in discussion with market parties for the first offshore project. The first tower could be delivered in 2021. "
What is the added value of Offshore Wind Innovators?
"Winning the jury prize of the Offshore Wind Innovation Award and our pitch during the Q-meeting have put us in the spotlight. About ten organizations contacted us during the meeting or afterwards. Offshore Wind innovators is a good network organization of innovative SME entrepreneurs. It makes sense to meet and learn from each other.”