Abstract: A vertical axis wind turbine system having a vertical mast with one or more turbine units supported thereon. The turbine units are of modular construction for assembly around the foot of the mast; are vertically moveable along the height of the mast by a winch system; and are selectively interlocking with the mast to fix the turbine units in parked positions. The turbine system and each turbine unit includes a network of portals and interior rooms for the passage of personnel through the system, including each turbine unit. The electrical generators, and other sub-components, in the turbine units are of modular construction that permits the selective removal and replacement of component segments, including the transport of component segments through the portals and interior rooms of the turbine system while the turbine units remain supported on the mast. The electrical generators are also selectively convertible between AC generators and DC generators.