Flywheel energy storage

Flywheel energy storage systems for use in vehicle propulsion has reached application in the light tram vehicle. They have also featured in pilot-production vehicles such as the Chrysler Patriot hybrid-drive racing car concept. Here, flywheel energy storage is used in conjunction with a gas turbine prime-mover engine, Fig. The drive was developed by Satcon Technologies in the USA to deliver 370 kW via an electric motor drive to the road wheels. A turbine alternator unit is also incorporated which provides high frequency current generation from an electrical machine on a common shaft with the gas turbine. The flywheel is integral with a motor/generator and contained in a protective housing affording an internal vacuum environment. The 57 kg unit rotates at 60 000 rpm and provides 4.3 kW of electrical energy. The flywheel is a gimbal-mounted carbon-fibre composite unit sitting in a carbo-fibre protective housing. In conjunction with its motor/generator it acts as a load leveller, taking in power in periods of low demand on the vehicle and contributing power for hill climbing or high acceleration performance demands.

European research work into flywheel storage systems includes that reported by Van der Graaf at the Technical University of Eindhoven. Rather than using continuously variable transmission ratio between flywheel and driveline, a two-mode system is involved in this work. A slip coupling is used up to vehicle speeds of 13 km/h, when CVT comes in and upshifts when engine and flywheel speed fall simultaneously. At 55 km/h the drive is transferred from the first to the second sheave of the CVT variator, the engine simultaneously being linked to the first sheave. Thus a series hybrid drive exists at lower speeds and a parallel hybrid one at higher speeds. The 19 kg 390 mm diameter composite-fibre flywheel has energy content of 180 kW and rotates up to 19 000 rpm.