That’s the brakes: Utilizing stored energy from public transit for grid services
A project by SEPTA aims to capture value from regenerative braking
pturing and storing the energy required to stop a train takes a lot of moving parts, but there are at least as many partners in a first-of-its-kind deal that provides an economic model for structuring regenerative braking project.
In a deal for the Southeastern Pennsylvania Transportation Authority (SEPTA), ABB, Constellation, Saft, and Viridity all played essential roles in bringing the project into being. The partners devised ways not only to generate, capture and store the energy from braking SEPTA trains, but figured out how to tap revenue streams to make the project economically viable.
Regenerative braking has been around for about a generation. It occurs when a vehicle, whether an electric car or a train, uses its motor to bring it to a halt. That throws the motor in reverse and, with some minor modifications, the motor becomes a generator pumping electricity back into the source that delivered it. But while the isn’t exactly novel, the idea that it could provide support for the wider grid is — and could advance the economics of battery storage by leveraging the ability to provide additional services to the grid network.
SEPTA’s brake project
In the case of SEPTA, the third rail is the source of electricity and if there was not another train following closely behind the braking train, the regenerated power was lost.
SEPTA had been looking for ways to capture that lost energy, but there were not enough savings from reducing demand to justify the costs — “not even close,” Erik Johanson, director of innovation at SEPTA, said.
Then in 2010 SEPTA partnered with Conshohocken, Pa.-based Viridity Energy and in 2011 won a $900,000 grant from the Pennsylvania Energy Development Authority to install a 0.8-MW wayside energy storage project at the Letterly substation in the Kensington section of North Philadelphia that serves the Market-Frankford train line.
SEPTA estimated that the project would be able to supply about 10% of the power demand at Letterly, reducing its electricity bills by more than $100,000. SEPTA was, in fact, able to reduce demand by 20%, but the real key to the success of the project came from what Viridity brought to the table.
Viridity provides the software interface between SEPTA and the PJM Interconnection, the wholesale market that provides power to a 13-state region including the greater Philadelphia area that SEPTA serves. That software monitors signals from PJM’s frequency regulation market, which requires incremental amounts of electricity to balance supply and demand.
Viridity’s interface gives SEPTA’s stored energy another use and, importantly, a source of revenue. If SEPTA does not need the stored energy to move a train, it can sell it into the frequency regulation market. SEPTA pays Viridity a service fee, and the companies have a profit sharing agreement for the revenues from PJM. Tyler Breiner, senior manager of partnerships and projects at Viridity, calls that approach “value stacking.”
“There is more than one way to make a deal pencil out,” Breiner said.
Following the success of the first project, SEPTA applied for another grant and in 2012, won $1.44 million from the Federal Transit Administration to install another wayside storage demonstration project. The second project was slightly larger, 1 MW, and included installation of super capacitors to buffer the discharge-recharge cycle of batteries thereby extending their lifespan.