Abstract: A rotor assembly includes a rotor mast, a rotor and a pivot arrangement. The rotor mast is for rotatable attachment of the rotor assembly to a support structure for rotation of the rotor assembly relative to the support structure about a rotation axis. The rotor has two rotor blades extending in a virtual plane in a longitudinal direction. The two rotor blades are arranged to be propelled by air flow. The pivot arrangement defines a pivot axis. The rotor is pivotably connected to the rotor mast for pivoting the two rotor blades simultaneously relative to the rotor mast about the pivot axis. The longitudinal direction and a projection of said pivot axis in the virtual plane enclose a constant acute angle in the virtual plane. A windmill and a wind farm includes the rotor assembly with a capacity in the range of 15-50 MW/km2.