It might be time to hit the brakes on energy storage. 

Meaning, in this case, that public transit systems now have the technology to fully harness the power that goes into bringing a train to a full stop. In most urban transit systems, that massive amount of energy is expended and dissipates as heat, just like the energy created when you bring your bicycle to a skidding halt. As far as the train or the bike is concerned, that energy is gone. 

But a number of recent innovations in Europe and North America promise to make rail systems significantly more energy-efficient by allowing the system to store the trains' braking energy in batteries stationed along the rail line. That energy will then be transferred to another train, which will use it to accelerate. 

In fact, there are even opportunities for rail networks to make money by distributing some of that stored electricity back to the grid. 

Until recently, the technology has only been deployed in small-scale pilot projects on both sides of the Atlantic. 

Now, one of those pilots has turned into a full-fledged, major-market commercial product after the Southeastern Pennsylvania Transportation Authority announced it will dramatically expand its use of a lithium-ion battery storage system that it put in place two years ago through a partnership that today includes Constellation, a Baltimore-based subsidiary of Exelon. 

The first two battery systems that were installed along one part of the rail system in 2014 were paid with a $900,000 state grant. But the expansion, which will include seven energy storage systems in a 8.75-MW network, will be entirely financed by Constellation, which has contracted with a Montreal-based division of ABB to construct the storage systems. 

Constellation will recoup its capital investment costs -- estimated by SEPTA to be between $12 million to $14 million -- by selling some of the stored energy back into the regional electric grid. It has contracted with a separate company, Viridity Energy, to take care of that. 

In a statement announcing the deal, SEPTA said the expansion is planned for the second quarter of 2016, with full implementation toward the end of the year. 

Ben Chadwick, director of distributed energy development for Constellation, said the project is also notable because it provides a storage solution that benefits the customer as well the grid and is being financed by a third party. 

The plan is for Constellation and SEPTA to both eventually make money off the project. After the company has recouped its investment, it and SEPTA will begin splitting the money generated from selling energy back to the grid. 

Neither Constellation nor SEPTA would provide any information on how long it might take the company to recoup its investment or how much revenue the project is anticipated to bring each entity involved. 

But, as Chadwick put it, "Were it immaterial, SEPTA wouldn't be pursuing this." 

Jacques Poulin, an executive at ABB in charge of the firm's public transportation energy storage initiatives, suggested that such systems will become a mainstay of rail networks. It's not just the electricity that trains demand, but the fact that they often demand such a large amount of it at certain times that make energy storage efforts so attractive.

Even in the U.S., where rail traffic isn't as high as it is overseas, local rail often accounts for the biggest electric load in a city. It's a demanding load, and, as Poulin explains, an inefficient one that is concentrated at certain times of day. 

"We believe that rail will more and more turn to energy storage to help reduce costs and to level the load, to make it a smoother load for the grid to manage," he said. 

Indeed, explained Chadwick, the batteries will be responding to a signal from PJM every two seconds that will tell it whether to push a bigger load back onto the grid. 

"PJM might need all of that 8.75 megawatts for two minutes," he said. "And then it won't (need anything)."

The batteries will simultaneously be responding to PJM's frequency regulation signal and the trains in need of additional power to accelerate. 

Giri Venkataramanan, a professor of electrical engineering at the University of Wisconsin-Madison who studies technologies aimed at making electrical generation more sustainable for residential, industrial and transportation uses, said that the project amounted to a "baby step" toward the goal of a truly smart grid, which he said is still likely several decades away. 

"If we have smart grids and we were able to coordinate (power) between trains, we wouldn't need these batteries," he said. 

While Venkataramanan said that such energy storage technologies represent a promising future for rail, he is skeptical that it will lead to a greater embrace of rail systems in the U.S. 

"In the U.S., the problem is political, it's not technological or economical," he said. 

Correction: An earlier version of this story referred to Constellation by its former name, Constellation Energy Group. Also, Constellation was not part of the original group of partner-entities involved in the project. 

http://www.energybiz.com/article/16/02/storing-sending-train-brake-power-grid