Williams Hybrid Power and Alstom cooperate to develop flywheel energy storage technology for Citadis trams
|Williams flywheel unit. Click to enlarge.|
Williams Hybrid Power, a division of the Williams group of companies that includes the Williams F1 Team, and Alstom Transport have signed an exclusive agreement that will see Williams Hybrid Power’s composite flywheel energy storage technology (earlier post) applied to Alstom’s Citadis trams by 2014.
After several years of research into energy storage, Alstom teamed up with Williams Hybrid Power to trial its composite MLC (magnetically loaded composite) flywheel energy storage technology which offers potential fuel savings of 15% when installed in public transport applications.
There is no mechanical connection from Williams’ flywheel storage; the unit connects using only electrical cables to transmit the energy back and forth, allowing the same vehicle packaging freedom as a traction battery. The company suggests thinking of its electric flywheel energy storage as an electro-mechanical battery or as an ultra high-speed electric motor/generator having a high inertia, composite rotor.
Originally developed for the 2009 Williams Formula One car, Williams Hybrid Power’s energy storage technology has since been introduced into applications such as London buses and the Le Mans-winning Audi R18 e-tron quattro.
The technology offers fuel savings and emissions reductions by harvesting the energy that is normally lost as heat when braking and turning it into additional power.
Flywheel energy storage technology offers higher specific energy than ultracapacitor technologies, but compared to batteries, the energy capacity is much lower. Thus, the flywheel is a very efficient short-duration energy accumulator that can capture and re-deploy large cumulative amounts of energy with little waste, Williams notes—i.e., it is ideally suited to kinetic energy recovery on trams because of their stop-start nature and high mass.
Flywheels also can operate efficiently at extreme ambient temperatures, unlike chemical batteries and capacitors. As a result, in vehicle installations less attention is required to control ambient temperature, ultimately allowing a less complicated, lower cost installation.
The flywheel rotor assembly is entirely composite apart from the rotor shaft at the neutral axis. An all-composite rotor is inherently safer than a steel hub and composite overlay construction, Williams says, as there is no metallic structure travelling at very high speed.
At the rotor’s maximum operating speed there is redundancy in design to prevent electrical and therefore rotational overcharge. This redundant, positive over-speed prevention is inherently safer than mechanically driven flywheel over-speed prevention methods, Williams says, where there is always a risk of over-speed via a malfunctioning mechanical drive.
From the very beginning we highlighted trams as an ideal application for our technology and to be collaborating with the market leader on this project is very exciting. We both share a common goal—developing the next generation of green transport technologies—and this agreement will hopefully prove pivotal in finding a solution that not only cuts carbon emissions but crucially cuts costs for the end user.—Ian Foley, Managing Director of Williams Hybrid Power