Technology Review – The automakers Volvo and Jaguar are testing the possibility of using flywheels instead of batteries in hybrid electric vehicles to aid acceleration and help engines operate more efficiently. The devices could reduce fuel consumption by 20 percent and would cost a third as much as batteries. Volvo will begin road-testing a car with the technology this fall.
The key system features were:
* A flywheel made of steel and carbon fibre that rotated at over 60,000 RPM inside an evacuated chamber
* The flywheel casing featured containment to avoid the escape of any debris in the unlikely event of a flywheel failure
* The flywheel was connected to the transmission of the car on the output side of the gearbox via several fixed ratios, a clutch and the CVT
* 60 kW power transmission in either storage or recovery
* 400 kJ of usable storage (after accounting for internal losses)
* A total system weight of 25 kg
* A total packaging volume of 13 litres
Flybrid have built and tested a 530 kJ, 60 kW storage system that weighs just 27 kg. This system is designed for vehicle mounted short-term storage applications and has been developed in conjunction with Magneti Marelli Motorsport.
The U.K. engineering firm Ricardo severed the mechanical connection between the flywheel and the transmission. Instead, energy from the flywheel is transferred to a transmission via magnets arranged around the circumference of the flywheel and in a ring outside the flywheel housing. By varying the ratio of the magnets in the flywheel to those arranged around it, it’s possible to make the flywheel spin six times faster than the ring around it, which simplifies the transmission of energy.
One advantage of flywheel systems over batteries is their compact size. “Most hybrids with batteries provide a 15- to 25-kilowatt boost of power. The flywheel can deliver 60 kilowatts in a way smaller package,” says Andrew Atkins, chief engineer of technology at Ricardo. The trade-off is that flywheels can’t supply energy for very long.
The Smart Energy 25 flywheel system includes a rotating carbon-fiber composite rim, levitated on hybrid magnetic bearings operating in a near-frictionless vacuum-sealed environment. The rim itself is fabricated from a patented combination of high-strength, lightweight fiber composites, including graphite and fiberglass combined with resins, which allow the flywheel to rotate at high speeds (16,000 rpm) and store large amounts of energy as compared to flywheels made from metals. To reach its operational speed, the system draws electricity from the grid to power a permanent magnet motor. As the rim spins faster, it stores energy kinetically. The flywheel can spin for very extended periods with great efficiency because friction and drag are reduced by the use of magnetic bearings in a vacuum-sealed environment. Because it incurs low friction, little power is required to maintain the flywheel’s operating speed.
Beacon has a 20-MW flywheel energy storage plant (a lot of smaller flywheel storage).