Information about rotor blades
For small wind turbines with a rotor diameter of up to 160 cm (1.6 m), there are different approaches to the optimal number of rotor blades, depending on various factors such as the desired speed, the area of application, and economic viability.
General Information:
*Two rotor blades:
Two-blade rotors are somewhat cheaper and lighter. However, they suffer from a less favorable mass distribution, which can compromise stability and may require additional shock absorbers to prevent vibration. The efficiency is slightly lower, at around 45%.
*Three rotor blades:
This is the most commonly used configuration, even for larger wind turbines. It offers a good compromise between efficiency, stability, and cost. A three-blade rotor reaches the ideal speed ratio for energy generation more quickly and has a more uniform rotation, which reduces material stress. In practice, the efficiency is around 48% for large turbines and around 40% for small wind turbines.
*More than three rotor blades (e.g., multi-blade rotors):
Such rotors, such as those formerly used on American "Westernmills" for pumping water, generate more torque at low wind speeds. However, they are generally less efficient for power generation because they create higher drag and rotate more slowly. The increase in energy yield would not outweigh the increased cost and additional expenditure on materials and construction.
Ideal rotors for small wind turbines:
Given the factors mentioned above and the fact that small wind turbines can suffer more from friction losses, three rotor blades are generally the best possible choice for good wind yield while maintaining stability and cost-effectiveness.
It is important to note that the optimal number of rotor blades also depends on the specific blade design (profile, length, twist), the rated power of the generator, and the prevailing wind conditions at the installation site. For maximum efficiency, it is always advisable to look for high-quality rotor blades that are tailored to the respective operating conditions.
