A rotor for a vertical axis wind turbine generator features a flywheel having first and second faces located opposite one another across a thickness of the flywheel, and a circumferential perimeter edge joining the first and second faces together around the central axis at a perimeter of the flywheel. A series of cavities are spaced radially inward from the circumferential perimeter edge and open into the flywheel from the first face on a path disposed circumferentially about the central axis. A series of permanent magnets carried in the cavities have the opposing poles of adjacent magnets facing in the same axial direction. The recessed magnet configuration avoids the separate magnet-retention means required for flush-mount configurations, and increases the performance of the generator.