Request ID: FOI-3293-2324 Date published: 15 January 2024
You asked
Hi there,
I am currently studying Product design at Nottingham Trent University and about to start my thesis. I have a keen passion for the underground and i’m looking at ways to make the it more efficient by capturing waste energy in the form of either heat, movement or wind. I have done some research and found that you have already listed how much electricity the network uses. I was wondering if you had the data percentage of how efficient the trains are as I can find out the potential energy savings. Any help would be great.
Kind regards,
Clarification received 28/12/2023: Hi there,
Thank you for your previous email, hope you had a good Christmas.
Sorry for not making myself clear enough,
Yes please, I am looking at what the difference is between the power input into the trains and how much is used for powering them. ie: for every 100kwh used how much does the traction motor use of that.
Kind regards,
We answered
TfL Ref: FOI-3293-2324
Thank you for your clarified request received by Transport for London (TfL) on28 December 2023 asking for information about the energy efficiency of the London Underground.
Your request has been considered in accordance with the requirements of the Environmental Information Regulations and our information access policy. I can confirm we hold some of the information you require. The different London Underground lines have different rolling stock types. Each of these rolling stocks have different characteristics and therefore perform differently in terms of traction efficiency performance. Whilst we do not directly measure this efficiency performance on our trains, we are able to calculate this based on measured values and modelling.
Using existing data, we can assume an average efficiency by taking the total traction energy used by a train and removing the losses and auxiliary loads (lighting, heating, aircon, etc). This yields an average figure of approximately 70% of total energy used by trains is used for train movement – with energy primarily dissipated through braking, motor efficiency losses and resistance forces. Please note that supply system losses and auxiliary loads each make up approximately 50% of the remainder. Depending on the application, the auxiliary loads should be included in the overall efficiency assessment – as these loads are still considered “useful” energy.
Some rolling stock types have regenerative braking capability. This is where a proportion of braking energy is transmitted back to the supply network. Where this is the case, energy loss due to braking energy is reduced and the total % of consumed power from the substations used for train movement is similarly reduced. This will give a reduced apparent % efficiency. If we include this regenerated energy, the average % of total energy used by trains for train movement is approximately 75%.
If this is not the information you are looking for, please do not hesitate to contact me.
Please see the attached information sheet for details of your right to appeal.
Yours sincerely,
Mary Abidakun FOI Case Officer FOI Case Management Team General Counsel Transport for London
