The nacelle is a large box on top of the tower that contains key wind turbine components. The tower arrives in cylindrical steel sections, which are hoisted and bolted together sequentially, starting with the base section anchored to the concrete foundation. It must be tall enough to prevent interference with normal day-to-day operations at ground level. A smaller, on-shore 2MW wind turbine has six parts: foundation, tower. The primary components of a wind tower are the foundation, the tower sections, and the nacelle assembly which houses the drivetrain, generator, and control systems, all topped by the rotor and blades.