The Importance of Wind Turbines for Renewable Energy

The American inventor Charles F. Brush invented the first automatically operated wind turbine in 1887. [1] Since then, multiple developments have contributed to the design of today’s modern wind turbine. And when grouped together into a wind farm, wind turbines are becoming an important source of renewable energy.

HAWT blades are designed like airplane wings in order to use lift to capture the wind’s energy. The airfoil design that they use makes one surface of the blade rounded, while the other is smooth and flat. [3] When air passes through the blades, a difference in pressure is created between the top and bottom of the blade. The introduction of the blade into airflow acts like an introduction of a force and causes the streamlines of the wind to curve and travel at different speeds. Since the airfoil must exert a force on the air to change its direction, the air must exert a force of equal magnitude but opposite direction on the foil. [4] This application of Newton’s Third Law generates the net lift force that the blade needs in order to rotate the shaft.

The size and material of the blades contributes greatly to the amount of power that turbines can produce. Materials that can produce the lowest amount of rotational inertia, like aluminum, are optimal because they allow the wind turbines to accelerate quickly if the wind speed increases. Low-mass materials are also ideal in order to control blade weight. [5] Larger blades with larger weights are constrained by gravity and will experience greater axial and tensile stresses. Finding the best size and material for rotor blades depends on the purpose of the turbine. Smaller power demands will reduce the need for larger blades and taller turbines.

Linking the rotor blades to...

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...tput. Stall is produced when there is a reduction in lift. The pitch of the blades can be changed by the active stall control within the braking system in order to produce stall and slow the rotational speed of the blades. [10]

The two main functions of the tower are to support the rotor and nacelle and to lift the entire setup to an elevation where the blades can operate safely. The height of the tower is dependent on wind velocity variation. The wind variation is due to the time of day and the elevation. At higher altitudes the speed of wind increases due to the low viscosity of the air. At nighttime, wind speed is higher because the atmosphere becomes more stable due to radiative cooling. [11] For most HAWTs, the height of the tower should be about two to three times the blade length in order to balance material costs against the more expensive active components.