Abstract: An airborne wind energy system includes a lift system, a wind power generating system, a tether, and a control system. The lift system including a substantially airtight chamber for storing lighter-than-air gases. The wind power generating system is coupled to the lift system and including two rotating assemblies and a generator. The tether is coupled to the wind power generating system and tethers the airborne wind energy system to the ground. The two rotating assemblies are coupled to the generator and arranged to rotate in opposite directions so that the generator generates electrical power when the two rotating assemblies rotate in opposite directions.