Flybrid Systems Composite Flywheels for Regenerative Braking Energy Storage
A British company called Flybrid Systems is producing carbon composite flywheel storage devices to capature and reused braking energy on formula 1 race cars (Yes, I know that this application is not at the forefront of sustainable energy technology). Here is some information from their website:
High-speed flywheel based energy storage systems using Flybrid technology are powerful, small and light giving a better power to weight ratio than existing automotive hybrid technologies. This higher power makes it possible to store more energy during short braking periods dramatically increasing system effectiveness. The systems are also very efficient with up to 70% of braking energy being returned to the wheels to drive the vehicle back up to speed. The devices are readily recycled and relatively inexpensive to make as they can be made entirely from conventional materials.
In the original Flybrid system the flywheel is connected to the transmission of the vehicle via a Continuously Variable Transmission (CVT) and manipulation of the CVT ratio achieves control of energy storage and recovery. When the ratio is changed so as to speed up the flywheel energy is stored and when the ratio is changed so as to slow down the flywheel energy is recovered.
A flywheel made of steel and carbon fibre which rotates at over
60,000 RPM inside an evacuated chamber
The flywheel casing features containment to avoid the escape of any debris in the unlikely event of a flywheel failure
The flywheel is 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
Magneti Marelli and Flybrid systems to collaborate on KERS energy storage for motorsport
Italian Motorsport electronics specialist Magneti Marelli and British high-speed flywheel specialists Flybrid Systems today announce the collaboration to develop a new energy storage solution for the Kinetic Energy Recovery System (KERS). The new product will deliver a high power electrical storage system for hybrid racing cars capable of deep depths of discharge with no performance degradation and a long service life.
The new product named Flywheel Capacitor consists of a high-speed carbon fibre flywheel incorporating Flybrid® technology connected to a high-speed electric motor generator using technology from Magneti Marelli, all managed by Magneti Marelli’s control electronics.
The device works by applying to the electric motor generator the recovered electrical energy captured from the vehicle during braking events. The energy is stored into the Flywheel Capacitor by speeding up the flywheel. During the acceleration events of the vehicle, the energy stored into the flywheel capacitor is returned to the vehicle by transforming the kinetic energy of the flywheel into electrical energy via the motor generator.
The Flywheel capacitor will not use chemical battery based energy storage systems.
The first Flywheel Capacitor to be developed will have a specification of 60 kW power and 600 kJ total storage capacity but the specification can be readily adapted to any vehicle requirements. Both partners will draw upon extensive experience with their own KERS products to deliver a working prototype in the next few months.
The volumetric energy density of this product is not impressive. The total system volume including the continuously variable transmissio (CVT) used to transfer energy to and from the flywheel is 13 liter. Based on the following picture it appears that the flywheel enclosure constitutes about half of the total volume. With an energy storage capacity of 400KJ (=111Wh) the volumetric energy density is 111/6.5=17Wh/liter. Lead acid batteries have an energy density of 40Wh/liter. Generally high speed composite flywheels are are quotes as having higher energy density than lead acid batteries although gravimetric energy densities (Wh/kg) are usually quoted, and I believe that generally speaking only the weight of the flywheel is considered in doing this calculation. I do not know how much the carbon fiber flywheel in the Flybrid system weighs. If the weight is 1kg then the gravimetric energy density would 111Wh/kg ( compared to lead acid batteries at 25Wh/kg).
Magneti Marelli, the codeveloper (along with Flybrid Systems) of a new version of the flywheel storage system using an electric generator/motor for power transfer rather than a CVT, has this to say about the virtues of flywheel storage vis a vis battery storage:
'Our know how is in the electrical side,’ explains Roberto Dalla, head of motorsport at the Italian firm. ‘We have lots of experience in alternators and electric motors, whilst we do not have a lot of experience in flywheels or other systems. We feel that the battery side of development is improving all the time. In the future, the scope for development of electrical systems is greater.’ Despite this, Dalla does not completely dismiss other approaches. ‘With the flywheel system, we were surprised by the dimensions and performance. The hybrid of the two systems, with a flywheel as the storage medium and the motor as a driver, could be an interesting possibility for the future. Up to this point, though, we feel our approach is correct, but only the future will show if we are right or wrong.
This is an intersting application of flywheel technology, but it does nothing to convince me that flywheels will fill anything other than small niches in the energy storage market.