London Underground (LU) used the new 'inverter' system at the Cloudesley Road substation on the Victoria line for a five-week trial, and in just one week of operation, the new technology recovered enough power to run a station as large as Holborn for more than two days per week.

The results show that the new green technology could allow LU to tap into a previously inaccessible resource, reducing its overall carbon footprint and saving as much as £6m every year for reinvestment in improving transport.

"The results of this project are really exciting and show huge potential for harnessing some of the immense energy in our Tube trains. The trial puts London at the cutting edge of this kind of technology and clearly demonstrates how energy from trains can be recovered to power Tube stations, making the network more environmentally friendly and cost effective. 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," said Matthew Pencharz, Deputy Mayor for Environment and Energy. 

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 that will also benefit residents.

LU is carrying out its largest programme of modernisation in decades, with major stations, trains, track and control systems being updated or replaced to meet the needs of the rapidly growing city and provide a 30 per cent increase in capacity across the Tube network.