Trackside Flywheel Energy Storage in Light Rail Systems

by Emil Morhardt

Light rail systems, like hybrid electric vehicles, use their electric engines to generate electricity when they are slowing down, a process called regenerative braking. In hybrid electric vehicles, the energy usually gets stored in lithium-ion batteries, which work well because they are comparatively light weight and not overly bulky. If neither of these were constraints, then flywheels or supercapacitors would be a better choice because they can deliver power faster and they take much longer to wear out. Of the two, flywheels are lighter, less bulky, cost less, and have longer lives according to a study by the UK Rail and Safety Standards board (Kadim 2009). If they are installed alongside the tracks rather than on the trains, weight and bulk are not very important but cost and lifetimes still favor flywheels. Gee and Dunn (2014) set out to estimate how much energy could be saved in an electric light rail system by using flywheel energy storage alongside the tracks; the result is 21.6% assuming the current mix of regenerative and friction braking, with even more savings if friction braking were reduced further. Additional benefits would include a 30% reduction in substation peak power, thus a smaller investment in substations would be required on new installations.The authors didn’t do an economic analysis, but cite another paper that suggests a payback period for installing such a system of only five years. What are they waiting for?

Kadhim, R. 2009. “Energy storage systems for railway applications. Phase 1 Report. ,” Rail and Safety Standards Board Report, T779, Interfleet Technology Ltd., Derby, UK, Sept. 2009.

Gee, A., Dunn, R., 2014. Analysis of Trackside Flywheel Energy Storage in Light Rail Systems. IEEE Transactions on Vehicular Technology DOI 10.1109/TVT.2014.2361865

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