The higher the number of blades, the greater the torque transmitted to the rotor shaft and the more the wind turbine can start at a low wind speed. Conversely, each blade causes turbulence for others, which can limit the speed of rotation of the wind turbine. In addition, a high number of blades leads to a greater wind resistance which prohibits their operation when the wind is too strong, and can increase manufacturing costs.
Two-blade machines exist but are reserved for smaller power sizes or uses in specific environments. In the case of a two-bladed wind turbine, the difference in forces that apply between the top blade and the bottom blade creates twists at the rotor axis. This results in faster wear of the equipment.
In a cyclonic environment, two-bladed wind turbines are well suited because they are lighter, easier to maintain and above all they can be folded down in the event of a cyclonic warning.
Regarding the evolution of the characteristics of the machines, the average height of the masts installed in New Zealand has continually increased in recent years. They have gone from 50 meters in the early 2000s to 90 meters on average today. The diameter of the rotor is also increasing, on the one hand because of a better control of the materials, on the other hand in order to be able to exploit a greater variety of sites.
This evolution of the mast height and the rotor diameter have led to an increase in the power of the machines and their production. Thus, wind turbines installed in NZ went from an average power of 1 MW in the first half of the 2000s to 2.4 MW in 2017.
One of the sustainable energy companies built wind turbines without blades that correct some of the old defects. From noise and landscape denaturing to a threat to birds and bats, the tri-blade wind turbines have been accused of many evils. For this reason, engineers designed turbines of another kind consisting of a large mast without blades, silent and safe for wildlife.
Made of lightweight materials, these wind turbines vibrate very quickly under the force of the wind, which allows to operate a turbine that produces electricity. This is line with the ethical electricity New Zealand initiative.
The lean structure of these turbines allows them to lower manufacturing costs and energy costs. However, the two prototypes that have been tested to date capture 30 percent less kinetic energy than traditional wind turbines.