Philly subway to capture energy from braking trains

September 1, 2010 9:15 AM PDT

by Martin LaMonica

Here's an unusual way to upgrade a subway system: add a giant battery.

Viridity Energy said Monday that it has been awarded a $900,000 grant by the Pennsylvania Energy Development Authority to build a system that will capture the energy from Philadelphia subway cars as they brake to enter a station.

(Credit: CC Infowidget/Flickr)
The regenerative braking system will collect energy in a large battery installed along the busy Market-Frankford Line. The stored energy will be used to power trains when they leave the station and to earn money from energy sold back to the grid.

"Essentially we're creating a microgrid that is integrated with the transmission grid and operated so that its optimized for efficiency and economics," said Audrey Zibelman, president and CEO of Viridity.

The project, which Viridity hopes to be operating by next spring, will have a battery with between 1 megawatt and 1.5MW of power, intended to replace the current system, which cannot capture all the energy from incoming trains.

With the battery in place, the system can power trains when they leave, cutting down on operating costs for Southeastern Pennsylvania Transportation Authority (SEPTA).

The battery will be able to make money, too, by providing services to the grid. Using its stored energy, it can make money from grid operator PJM by supplying quick bursts of energy to maintain a steady frequency. SEPTA can also draw energy from the grid at off-peak times and supply it at peak times when the utility is looking to lower usage because energy prices are high.

Viridity's hosted software is like a "network operating service" that optimizes how the energy is pulled into and dispatched from the battery, said Zibelman. The company, which makes money by getting a percentage of customers' revenue, is now evaluating what types of batteries it will use, she added.

"Electric vehicles are on everyone's mind right now as where we need to go, but we have an electric vehicle system already sitting here. Let's use those first," Zibelman said. "It's something could be done in almost any transit system.

SEPTA estimates that it can save $500,000 a year on its electricity spending. If the project is successful, SEPTA hopes to replicate the model system-wide, Joseph Casey, SEPTA general manager said in a statement.

Updated at 9:45 a.m. PT with corrected term for the battery's expected power.

Martin LaMonica is a senior writer for CNET's Green Tech blog. He started at CNET News in 2002, covering IT and Web development. Before that, he was executive editor at IT publication InfoWorld. E-mail Martin.
Topics: Transportation, Batteries and energy storage, Smart grid

Tags: subways,Viridity Energy

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Add a Comment (Log in or register) (4 Comments) prev next by Franko234 September 1, 2010 10:17 AM PDT

The Montreal metro has been doing that since the 70's

Like this Reply to this comment by fudbuster77 September 1, 2010 1:09 PM PDT
In the early 1900's, many electric railroads used regenetive braking to help power other trains. The Milwaukee Road would use a train going downhill on one side of a mountain pass in the Rockies to use regenetive braking to help add power to a train going up on the other side.

Everything old becomes new again.
Like this Reply to this comment by Joe Real September 1, 2010 2:23 PM PDT
What is the typical roundtrip efficiency of the system? Would the amount of energy saved be enough to pay off the added investment?

Like this Reply to this comment by GRobLewis September 1, 2010 7:36 PM PDT
New Rule: anybody writing about energy technology must pass a course in basic physics. "1 megawatt" is not a measure of battery capacity! 1 megawatt-hour might be.

In similar articles, I have seen assertions that a new power plant has an output of "10,000 kilowatts per year." This is a meaningless statement that, like the above claim, has no physical interpretation.

Innumeracy strikes again.

Read more: http://news.cnet.com/8301-11128_3-20015306-54.html?tag=mncol;posts#ixzz0yOj6evBT