Request ID: FOI-3010-2223 Date published: 02 March 2023
You asked
I need information on certain characteristics of the regenerative braking systems you use, particularly any system using flywheels. The information that would be useful is
• The type of regenerative braking used, the rolling stock, and the tube line it is used on
• The weight of the energy recovery system
• The theoretical/actual energy recovered.
• The overall efficiency of the regenerative braking system.
• Information on how the recovered energy is stored and reused
• If a flywheel system is used the weight of the flywheel and materials used in its construction
• A schematic of the system is used
If Transport for London uses different systems I would be most grateful for an example from a flywheel-based system and one other.
We answered
TfL Ref: FOI-3010-2223
Thank you for your request which we received on 13 February 2023, asking for information about flywheel regenerative braking systems.
Your request has been considered in accordance with the requirements of the Freedom of Information (FOI) Act and our information access policy. I can confirm we hold some of the information you have requested. You specifically asked for;
• The type of regenerative braking used, the rolling stock, and the tube line it is used on
It’s always electric, returning power to the conductor rails for use by other trains. We have this on all passenger trains used on the Central, Waterloo & City, Jubilee, Northern, Victoria, Metropolitan, Circle, Hammersmith & City and District lines as of 2023. Replacement fleets for the Piccadilly and Bakerloo lines will have regenerative braking on a similar basis.
• The weight of the energy recovery system
We have no flywheel energy storage systems, regenerative braking is available for instantaneous re-use only.
• The theoretical/actual energy recovered
We estimate it’s 129.9WGh per annum for the subsurface railway (Metropolitan, District, Hammersmith and City and Circle line) alone. This is a theoretical estimate between energy consumed in a theoretical SSR without regenerative braking and the one we operate.
• The overall efficiency of the regenerative braking system
From measurements on the Metropolitan line we estimate 26% of the energy used by trains is gainfully re-used through regenerative braking.
• Information on how the recovered energy is stored and reused
We don’t store energy. If the line is unreceptive, braking energy is dissipated in on-board resistors. Regenerated braking energy is transmitted to the London Underground high voltage distribution network and re-used by other trains.
• If a flywheel system is used the weight of the flywheel and materials used in its construction
We have not used any on-board flywheel devices on the London Underground.
• A schematic of the system is used
Assuming this relates to flywheels, we don’t hold the information.
If Transport for London uses different systems I would be most grateful for an example from a flywheel-based system and one other.
We don’t use flywheel based systems.
Please see the attached information sheet for details of your right to appeal as well as information on copyright and what to do if you would like to re-use any of the information we have disclosed.
Yours sincerely
Eva Hextall FOI Case Management Team General Counsel Transport for London
