Philadelphia subway trains are the next to jump on the energy innovation bandwagon, by using the energy they create from braking to help power other trains and possibly even the electric grid.

Basically, a large battery will capture the kinetic energy the trains create while braking, and then that energy will be supplied to the Southeastern Pennsylvania Transportation Authority (SEPTA) for its own uses or fed into the grid. This is quite similar to the regenerative braking systems in use by hybrid cars and electric vehicles, but it is a system hardly used by trains despite the great potential there.

“Philadelphia subways use regenerative braking to some degree now; kinetic energy is converted to electricity that is returned to the system through the third rail. But the system still loses at least half the energy as heat,” Jason Kambitsis of Wired reports.

The Market-Frankford line, the line with the highest ridership in the system, will be the line testing out this energy project. The energy created by this project will be used by accelerating trains on the line, stored for future use, or returned to the grid.

“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,” Andrew Maykuth of the Philadelphia Inquirer writes.

Funding and Pilot Project Launch

The project is supposed to launch in the spring and is expected to save SEPTA $500,000 a year. Although this is not a ton compared to the $20 million SEPTA spends each year powering its subways, trains, buses, and electrified trolleys, if this system were used at all of the 33 electrical substations in the railway network (which it would like to do if this pilot project goes well), SEPTA could reportedly cut their energy consumption a full 40%!

To fund this $1.5 million smart-grid/energy innovation pilot project, SEPTA and smart-grid company Viridity Energy received a $900,000 grant from the Pennsylvania Energy Development Authority. Viridity is underwriting the rest of the cost.

 cleantechnica.com