The X-Energy sub-project X-Rotor – Zweiblatt analysed the physical and economic differences between two-bladed and three-bladed 20 MW offshore wind turbines. The aerodynamic efficiency of a two-blade turbine with a similar design is only around four percent lower than that of a three-blade turbine. If the rotor of the two-blade turbine is only around two percent larger, the power generation is identical. In the sub-project X-Rotor – Zweiblatt, potentials were verified and new knowledge bases created using simulations that were as realistic as possible and various economic models. The focus of this comparison lay on the most equivalent system design possible. In addition, a precise comparison of the (dynamic) loads of two-blade and three-blade systems was developed in the project.
The fundamental question and motivation for the research project was: Does it make sense that the majority of today's offshore wind turbines are three-bladed turbines, whose concept was originally developed for onshore use and then transferred to the offshore sector? For offshore use in particular, however, two-bladed turbines are seen as a way of reducing the levelised cost of energy. This is because two-bladed turbines offer cost advantages throughout the entire life cycle, including transport, construction, maintenance, demolition and recycling, which is particularly important offshore.
Results
The project yielded many insights regarding two-bladed turbines. Important published elements of the research project are the following:
- the aerodynamic design of a blade structure of a two-blade turbine, based on an existing three-blade turbine, with the same quasi-static power curve
- the structural scaling of rotor blades of a two-blade turbine with the aid of FEM
- comparing the advantages and disadvantages of two-blade turbines with different design speeds
- the design of a speed exclusion zone and active tower dampers for two-blade and three-blade systems
- objective regulator tuning with the aid of a control cost criterion developed for this purpose
- the comparison of fatigue and extreme loads of different concepts of 20 MW two-blade turbines with a 20 MW three-blade turbine on the basis of a similar power curve
- development of a new method of damping active pitch-pendulum velocity coupling that reduces extreme loads and the pitch effort of pure active pitch-pendulum angle coupling in extreme load scenarios
The results from the completed X-Rotor two-blade sub-project were utilised and continued in the project X-Zweiblatt Floating.
A more detailed presentation of the results of X-Rotor Zweiblatt can be found in the final report of the sub-project.
