Urban Transport

London Tube trains recover enough energy to power stations

Future Underground rolling stock will include energy-saving technologies
Future Underground rolling stock will include energy-saving technologies
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Future Underground rolling stock will include energy-saving technologies
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Future Underground rolling stock will include energy-saving technologies

According to Transport for London (TfL), the city's Underground carries 1.2 billion passengers a year over 402 km (250 mi) of track, with some stations handling 89 million passengers annually. That adds up to a fleet of trains covering 76.2 million km (47 million mi) and an energy bill that defines "enormous." In an effort to make the system greener and cheaper, the authority carried out a five-week trial of a regenerative braking system billed as a "world first" that could slice 5 percent off London Underground's energy bill and save up to £6 million (US$9 million) per year.

The new technology uses an "inverter" energy capture system that recovers energy from the train's brakes and feeds it back into the mains in the form of electricity. In hybrid and electric cars, such recovery systems can help improve range, but in large heavily-packed passenger trains running regularly in one of the most heavily traveled cities in the world, the effects can be significant.

The trial was carried out at the Cloudesley Road substation on the Victoria line and was part of a system-wide modernization program that involves repairing the existing infrastructure, and introducing updated technology, new rolling stock, and new lines. In the test, in one week, the system recovered enough energy to power Holborn station for over two days per week. According to TfL, the technology can recapture up to 1 MWh of energy per day, which could run 104 homes per year.

TfL claims that the new technology could reduce the Underground's carbon footprint, but another bonus is the knock-on effect of recovering energy. Normally, braking a train turns the energy into heat, which gets trapped in the Underground's tunnels and needs to be carried away by air conditioning systems. The inverter technology means less heat, less need for air conditioning, and greater energy savings.

Source; Transport for London

3 comments
John Potter
Ahhh, regenerative braking probably better in a underground situation. Eurostar's was a pain, Emergency Elec. Discharge for body on track and forced to wait 5 mins for all trains stopped and report in, only then track rescue. stressful times.
jakey1234
And not only less heat but also less wear and tear on the brakes. Surprised that this has not been done before.
Paul Gracey
Regenerative braking was used in a test on a NY City Subway car sometime back in the nineteen seventies by Lockheed. Electric motor efficiency and control algorythms for its use in those days were not as high as it has become today, so the gains were probably too modest to sell the idea back then. Also It added a complex system to each DC powered car still using a system of control devised by Frank J. Sprague in the 19th and early 20th century. The new Transit Systems are all electronic and microprocessor controlled, so this probably only adds a small amount of the same sort of control equipment to divert energy from dynamic brakes to regen.
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