The X-Energy sub-project X-Rotor - Zweiblatt is investigating the physical and economic differences between two-bladed and three-bladed 20 MW offshore wind turbines. The aerodynamic efficiency of a two-bladed turbine with a similar design is only around four percent lower than that of a three-bladed turbine. If the rotor of the two-blade turbine is only around two percent larger, the power generation is identical. In the X-Rotor – Zweiblatt sub-project, attempts are being made to verify potentials and create new knowledge bases using simulations that are as true to nature as possible and various economic models. The focus of this comparison is on a system design that is as equivalent as possible. In addition, a precise comparison of the (dynamic) loads of two-bladed and three-bladed turbines is being developed in the project.
Three-bladed wind turbines are currently omnipresent. The basic turbine concept has remained almost identical for many years, both on land and on water and for different size variations. However, the typically wide blade structure of two-bladed turbines offers physical advantages that enable a reduction in rotor mass and costs, particularly for extreme dimensions. In addition, the saved blade leads to a further reduction in costs, as one less blade has to be built, transported, installed, maintained, torn down and recycled or disposed. In addition, a smaller wind contact area reduces wind loads in storm conditions and the parking position of the rotor in the T-position offers better access to the two-blade system by helicopter for maintenance work.
Despite all these advantages, there are also challenges, particularly in terms of turbine dynamics. With a two-bladed wind turbine, the forces are less evenly distributed over the rotor surface. In addition, there is a constantly changing orientation of the rotor inertia axes and cyclical excitation from the opposite rotor blades, which are located at the strongest and weakest wind heights.
However, there are also other possible solutions: For example, a pendulum hub can be used which, similar to a seesaw, does not transfer any bending moment to the suspension when the rotor blades are subjected to different loads. In addition, modern control technology in conjunction with sensors, for example through model-predictive or individual blade control, enables further measures to reduce loads.
The results from the completed X-Rotor two-blade sub-project will be used and continued in the project X-Zweiblatt Floating.
