They call it a Nacelle- check out wikipedia-
Nacelle (wind turbine)
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Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into the nacelle.
200-ton wind turbine nacelles being unloaded at a seaport.
A nacelle (pronounced /nəˈsɛl/) is a cover housing that houses all of the generating components in a wind turbine, including the generator, gearbox, drive train, and brake assembly.[
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