Southeastern Pennsylvania Transit Authority (SEPTA) operates the sixth largest public transportation system in the United States, serving almost four million people in and around the city of Philadelphia.

Eighty percent of SEPTA’s annual electricity consumption of 500 million kilowatt-hours is used to power trains, of which 60 percent goes into kinetic (motion) energy. However, much of this energy is wasted every time a train brakes as it pulls into a station. Capturing and recycling this energy could reduce SEPTA’s overall power consumption by more than 10 percent.

SEPTA selected ABB to provide a solution that would capture, store and reuse the surplus energy generated by braking trains, and integrate it with optimization software to enable the sale of frequency regulation and wholesale electricity services back to the regional power market.

The solution is based on ABB’s Envistore™ Regenerative Energy Storage System.

Normally, Envistore uses double-layer super capacitors to regenerate train braking energy and reuse it to assist acceleration. For the SEPTA project, ABB replaced this storage medium with a much larger lithium-ion battery system that can store large amounts of excess braking energy, and later return the energy when market energy prices increase, typically during peak hours and hot temperature conditions. The software is provided by smart grid energy provider Viridity Energy.

The solution has been operating successfully since April this year in a substation on the busy Market-Frankford rapid transit line in Philadelphia, where it serves five stations and regenerates energy from almost 400 daily weekday train stops at each station.

The solution is expected to recycle in excess of 1,200 megawatt-hours of energy a year and generate annual savings and/or revenues of up to $440,000. With savings and revenues of this magnitude, the project is understandably generating a lot of excitement in rail transportation and energy efficiency circles worldwide.

Envistore was recently selected by AGP Metro Polska for the new metro line 2 in Warsaw, where it will recycle the braking energy from metro stations and gravitational energy from passing under the Vistula river. It is part of a large package of ABB rail solutions for the new metro line that includes medium voltage substations and a network management system.