Energy in the Future series: Regenerative braking
Regenerative braking can be used to reduce harmful emissions and costs. For example, London Underground has utilised regenerative braking on newer stock, allowing 20% of used energy to return to the network. Lower friction braking reduces brake wear and dust build-up due to friction, leading to a reduction in maintenance costs and improved air quality, respectively. The technology can also be used in conjunction with storage systems to shift the use of energy to a time where consuming energy directly from the grid may be more expensive (peak shaving), resulting in cost savings. Reversible substation systems have also been successfully used on electrified lines, thus limiting wasted energy, providing voltage stability and reducing tunnel temperatures through the removal of on-board brake resistors. By using reversible substation systems, London Underground has been able to store enough energy to power a medium-sized station for two days a week and could save approximately £6m. a year. Some reversible substation system suppliers state that the number of traction substations could reduce by 20%.