The "OptiBine" research project

The research project Optimized low-speed wind turbine (short: OptiBine) dealt with the topic of small wind energy between 2012 and 2015. It was part of the Plastics and Elastomer Technology course at the former University of Applied Sciences Würzburg-Schweinfurt (now Technical University of Applied Sciences Würzburg-Schweinfurt). OptiBine was funded by the Bavarian State Ministry of Education and Culture, Science and the Arts. The initiator and head of the project was Prof. Walter Baur (now emeritus).

Modern wind turbines have rotor diameters of up to 126 m and an output of over 7 MW. This is enough power to supply an average of 4,300 single-family homes with electricity. In addition to these gigantic power generators, there are also small three-bladed turbines designed for private households. These small wind turbines usually have a diameter of a few meters and an output of a few kW to a maximum of 100 kW.

However, this three-bladed type of wind turbine has disadvantages in that they have to operate at very high speeds in order to harvest the energy from the wind. As a result, these turbines, known as high-speed turbines, generate noise that can be particularly disturbing in residential areas. The shadows they cast can also be perceived as unpleasant. The fact that the high-speed turbines only start up at relatively high wind speeds also makes them unsuitable for use as energy converters in built-up residential areas with little wind.

The aim of OptiBine was therefore to develop a rotor that works without the disadvantages described above. A well-known design was to be used: the "Western windmill". These windmills, equipped with around 30 metal rotor blades and measuring a few meters in diameter, were developed in the middle of the 19th century and helped drive the conquest of western North America. And even today they are still used worldwide as drives for water pumps. Due to the large number of rotor blades, they have a significantly lower rotational speed and are therefore referred to as low-speed wind turbines.

In the modern wind industry, they are considered to be significantly less efficient than three-bladed turbines, but this is not particularly surprising given that their design is over 150 years old. Together with students, OptiBine has succeeded in improving the efficiency of this low-speed turbine and bringing it closer to that of modern three-bladed turbines. State-of-the-art materials such as fiber-reinforced plastics were used for this purpose. Computer simulations such as the finite element method and numerical fluid mechanics were also used to optimize the strength and aerodynamics of the rotor blades.

The measurements to determine the efficiency were carried out in a "moving wind tunnel". For this purpose, the manufactured low-speed rotor was mounted on a wagon of the Mainschleifenbahn, whose speed simulated the incoming wind.