Wind turbine
Although there are many ways that the wind can be used to turn a turbine, this site concerns the 3-bladed horizontal-axis upwind design that is usually used.
The only major design difference is direct-drive versus gearbox-driven generators. The former used to be primarily used in smaller wind turbines for on-site home and farm use but are increasingly used in larger wind turbines for the advantage of fewer moving parts. The gearbox on wind turbines is a common site of mechanical failure. Direct-drive generators, however, because the rotor speed is slower, require many – up to tenfold – more magnets, about a third of whose composition is the rare earth metal neodymium. Although rare earth metals turned out to be – well after receiving the classification – not all that “rare”, their mining and processing are highly toxic and environmentally harmful, and the supply is therefore limited.[1]
The basic design begins with a steel tubular tower that on land is anchored to a steel bar–reinforced concrete foundation which may be further anchored by drilled pilings. At the top of the tower sits the “nacelle” (named after the engine housing of an aircraft) containing the rotor shaft, gearbox, and generator. At one end of the nacelle, three airfoil blades are connected to a hub that is connected to the rotor shaft.
The nacelle can be turned at the top of the tower to keep the blade assembly perpendicular to the wind and upwind of the rest of the nacelle. And each blade can be rotated on its axis to adjust its pitch, changing the amount of “lift” from the wind that moves it around the hub so that the rotation speed remains fairly constant.