A power generation assembly for use in generating electrical power from air or water currents includes a rail system including at least one rail and a vane assembly, drivable by the air or water currents. A car assembly is slidably mounted to the rail and coupled to the vane assembly: wherein movement of vanes of the vane assembly generates linear movement of the car assembly. An electrical energy generating system includes two or more independent sets of stator windings carried by the rail system, and a piston, carried by the car assembly, wherein linear movement of the piston relative to the stator windings generates electrical energy. A switching system is operable to controllably and individually activate each of the two or more independent sets of stator windings.