Final answer:
The greatest efficiency for wind turbines is achieved using three blades. This design is the most efficient and poses a lower safety risk to birds. It can convert approximately 50% of wind energy into power, operating optimally within specific wind speed ranges.
Step-by-step explanation:
Research has shown that the greatest efficiency for wind turbines is achieved using three blades. The three-blade design is not only the most efficient; it also possesses a safer lower tip speed compared to wind turbines with two or one blade. The efficiency of a wind turbine's blades is affected by how well they can engage the wind, and a three-bladed rotor is able to extract roughly 50% of the energy from the wind at its optimal speed.
According to Figure 12.4, which illustrates theoretical and practical turbine efficiencies, a turbine with three blades operates below the Betz limit and within the optimal tip speed to wind speed ratio. As for safety concerns, three-blade turbines have a lower risk to birds due to their tip speed being closer to bird cruising speeds. For turbines designed with three blades, any increase in wind speed beyond the rated maximum power output can risk damage, so the blades are twisted to maintain constant power output and prevent over-speeding in high winds.