SEPTA to test the capture, reuse of subway energy

SEPTA announced a pilot project that would capture electricity generated by braking subway trains, similar to how a hybrid automobile produces power when it slows down. The electricity will be stored in a large, railside battery array and reused when the train accelerates, according to a report in the Philadelphia Inquirer. The system is expected to reduce electrical power purchases 10 percent to 20 percent at each location of the batteries, said Andrew Gillespie, SEPTA's chief engineering officer for power. The power-storage system is potentially so large - each battery array would store one megawatt of power - that SEPTA could further reduce its electric bill by buying cheap power at night to use or resell during expensive peak hours. And SEPTA also could collect fees from the regional grid operator, PJM Interconnection L.L.C., by providing power on short notice - one or two seconds - to stabilize regional power flows on the grid. The pilot project, involving a single battery array at a SEPTA electric substation in Kensington, would cost about $1.5 million. The Pennsylvania Energy Development Authority is underwriting the project with a $900,000 grant. Viridity will underwrite the remaining capital cost, Zibelman said. If the project proves economic - Viridity estimates one battery array will generate $500,000 a year in value - SEPTA envisions installing the technology at all 33 electric substations that serve its subway and trolley lines. The system will take advantage of regenerative-braking capacity already installed in the Market-Frankford Line and SEPTA's electrified buses and trolleys. When applied, the brakes now convert the train's kinetic energy into electricity, which is transmitted into the third-rail system for use by other trains. But when there are no other trains nearby to consume the electricity, the power is lost. Excess electricity from the brakes is converted into heat that is dissipated from vents in the carriage rooftops. About half the power produced by the regenerative brakes is now lost, Gillespie said. SEPTA says the batteries, in addition to capturing the regenerated power that is now lost, will help increase the system's electrical efficiency and stabilize the voltage - it operates on 600-volt direct-current power.