London Underground (LU) is trialling a new system to recuperate the energy lost from braking trains.
An 'inverter' system was installed at the Cloudesley Road substation on the Victoria line for a five-week trial and in just one week of operation, the technology recovered enough power to run a station as large as Holborn for more than two days per week.
The trial is the first of its kind and could reduce the carbon footprint of the system as well as lowering energy costs.
LU estimates that £6m could be saved annually if fully rolled out, which would be reinvested into the train network.
As well as saving energy, the technology has the added benefit of lessening the amount of heat generated by trains braking in tunnels, which in turn would reduce the energy required to operate LU's cooling systems.
The results indicated that one megawatt hour of energy can be captured per day, equivalent to the power used by 104 homes annually.
Matthew Pencharz, deputy mayor for environment and energy, said that the trial places London at the “cutting edge” of technology of this type and would help to make the network more environmentally friendly.
“The results of this project are really exciting and show huge potential for harnessing some of the immense energy in our Tube trains,” he said.
“This complements our wider work to make other forms of public transport cleaner and greener, including our buses, where we have introduced hybrid and zero-emission technology.”
Chris Tong, LU's head of power and cooling, said: “This state-of-the-art regenerative braking system has the potential to transform how we power stations across the TfL network, unlocking massive power savings and significantly reducing our energy bills.
“We are committed to doing more to reduce our energy use and this technology - a world first for metro railways - is one of a number of innovations we're embracing to lower our environmental impact.”
LU is currently implementing a programme of modernisation, with major stations, trains, track and control systems being updated or replaced with the aim to provide a 30 per cent increase in capacity across the network.
The trial follows a number of other measures put in place by the Mayor and Transport for London to 'green' the capital's tube system.
In January, it was announced the historic Greenwich Power Station would be revamped to transform it into a low-carbon power generator for the Tube network.
Its six new gas engines will replace existing boilers and provide cheaper, cleaner power for the Tube, with waste heat being channelled into a new local heat network for nearby residents.