High Speed Flywheels for Vehicular Applications

This article analyzes two business cases using flywheels in vehicles. Firstly, a diesel based car ferry, in Gothenburg, performing 102 5 minute long journeys per day. Secondly, a diesel based city bus. A theoretical analysis of the benefits, technical and economical, of electrifying these vehicles using flywheels is performed. As basis for the analysis is a constructed high-speed flywheel, designed to store up to 870Wh at a rotational speed of 30 000 rpm. The rotor of the flywheel is constructed from a permanent magnet machine surrounded by a shell of composite material. The flywheel is optimized for low loss as well as low cost. The economical analysis of the two business cases show great potential for cost reduction by either utilizing a flywheel as temporary energy storage for capturing regenerative braking energy or replacing the diesel generator completely as main energy storage. The main material cost of the constructed flywheel pertains to the position sensors and the permanent magnet material used in the magnetic bearing.