Practical wind turbines are designed to work between certain wind speeds. The 'cut out speed' is determined by the ability of the particular machine to withstand high wind. The 'rated speed' is the wind speed at which the particular machine achieves its maximum rated output. Power Output from a Wind Turbine as a function of Wind Speed. In figure 2, V c is the cut-in speed at which the turbine starts to produce power, V r is the rated speed at which the turbine reaches it's rated power and Vf is the furling speed, which is the wind speed at which the machine shuts down to avoid damage.
P r is the rated output of the turbine.
This curve would be typical of an optimal horizontal two or three bladed machine. The machine follows the peak power available from the wind until it reaches the generator capacity and then stall regulates to maintain a steady output until shut down. The blades of the rotor are designed to spin in the wind, driving the turbine generator. Sometimes gearing is used to increase the frequency for electricity generation. This generates the electricity when there is sufficient wind to rotate the blades.