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Philadelphia subway brakes for energy savings

By | September 2, 2010, 4:00 AM PDT

Electric trolleys still cruise the streets of Philadelphia. Dating to 1892, Philly’s transit system is one of the oldest in the U.S. It’s also the country’s sixth largest.

A section of it is about to get an energy upgrade.

A $900,000 pilot project is on its way to save, and possibly profit from, SEPTA’s energy use. Viridity Energy plans to recycle the energy of trains coming into the station for use of the trains when they pull out.

Funded by the State of Pennsylvania, the project entails a huge battery (with 1 to 1.5 megawatt capacity) that will capture energy from the regenerative braking system of the trains, as they screech into some of the substations along the popular Market-Frankford Line.

By lessening SEPTA’s dependency on electricity from the grid (remember, Pennsylvania is coal country), the system, according to Viridity, might cut SEPTA’s carbon dioxide emissions by 1,258 tons each year.

From our friends at CNET:

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.

If successful, the idea may travel to more of Philly’s 38 substations. As is, SEPTA estimates the project will be worth $500,000 to them.

Joseph Casey, SEPTA’s general manager, says in a statement:

Upon implementation, the storage system will serve as a foundation for measurable gains in both energy efficiency and voltage stability in this critical corridor, providing a replicable and scalable model for broader system-wide implementation. By moving towards energy storage, SEPTA will be assuming a leadership role among transit agencies.

New York City MTA, are you listening? (Or are you too busy raising my fare and cutting service.)

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Melissa Mahony

About Melissa Mahony

Melissa Mahony was a contributing editor for SmartPlanet from 2010 to 2011.

Melissa Mahony

Melissa Mahony

Contributing Editor, Energy

Melissa Mahony has written for Scientific American Mind, Audubon Magazine, Plenty Magazine and LiveScience. Formerly, she was an editor at Wildlife Conservation magazine. She holds degrees from Boston College and New York University's Science, Health, and Environmental Reporting Program. She is based in New York.

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Melissa Mahony

Melissa Mahony

Melissa does not have financial holdings that would influence how or what she covers. She currently works for the Wildlife Conservation Society as an editor. Should Melissa cover a topic in which the WCS is involved, she will disclose this fact in her writing.

She writes for SmartPlanet and is not an employee of CBS.

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+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
What are SEPTA?s current carbon dioxide emissions each year?
Posted by gwwogreen
2nd Sep 2010
+1 Vote
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RE: Philadelphia subway brakes for energy savings
"capture energy from the regenerative breaking system of the
trains"

I hope this isn't going to break the trains.

Perhaps "braking system" was intended?
Posted by BaapidMakwa
2nd Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
Doh! Thanks BaapidMakwa! It's fixed.
-Melissa
Posted by Melissa Mahony
2nd Sep 2010
+1 Vote
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RE: Philadelphia subway brakes for energy savings
I suggest using flywheel batteries instead of lead acid. They are better for fast charge/discharge like accel and decel trains.

They have a very large flywheel spinning on a air bearing and a generator connected. During decel, energy flows in, making the generator into a motor and accel'ing the flywheel. During acelleration of the train, the process is reversed.

Active Power is one vendor -- I am not associated with them in any way.
Posted by TCMCATCMG,BTBSGOF
2nd Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
I'm confused. Are there going to be batteries on trains or is the
energy going to be transmitted from trains to a storage system in
the station (or other stationary location)?
Posted by davagain
2nd Sep 2010
+1 Vote
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RE: Philadelphia subway brakes for energy savings
Hi: Exciting idea. If i recall correctly, subway trains run on 600 volts DC delivered via a third rail or overhead trolley. That would be alot of battery in a railcar; a "caboose" perhaps. Probably it would be located centrally. In that way all trains on the line would either take or deliver power onto the system.

The flywheel sounds interesting, but i understand they are not very efficient.
Posted by General Ludd
2nd Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
regenerative braking is not new (around since about 1900, when, by the by, it caused a nasty freak accident when all the streetcars in Birmingham, England braked simultaneously and unloaded the generators). And there's a mine railway in Africa which is a net power producer. But the battery bit is new (vanadium maybe, the article doesn't say) and may be the first of many
Posted by jw@...
2nd Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
Did you know that there is art beneath your feet in the NYC
subway? Check out MEET ME AT THE CORNER, Virtual Field Trips
for Kids and the episode about The Art in Transit Program.

http://www.mmatc.meetmeatthecorner.org/episode/New-york-
+subway-art-under-your-feet
Posted by Donna Guthrie
2nd Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
They are paying $900,000 for a system worth $500,000? Who is paying the additional $400,000? Environmental benefits are wonderful, but where are the cost savings? And you want NYC MTA to implement this, and lower your fare? Please explain.
Posted by NJnewsource.com
2nd Sep 2010
+1 Vote
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RE: Philadelphia subway brakes for energy savings
One ton of carbon (coal) produces 3.3 tons of carbon dioxide, 1258 tons of CO2 is produced by burning 381 tons of coal, probably about one days worth at a coal burning power plant. At ~ $50.00 per ton of coal we're talking about $19,000 per year, a 47 year payback considering the $900,000 pilot cost. HMMMM.
Posted by fw32
2nd Sep 2010
+1 Vote
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RE: Philadelphia subway brakes for energy savings
The most efficient braking system is one you never use. How about finding a way to adjust the schedule so that the trains can take more time to stop and go and use brakes less?

Of course, I realize how much I annoy other drivers on the road when I do that with my hybrid here in Utah, so it is rather hard to imagine the reaction of all the passengers on the East Coast, both those on the train and those waiting to get on.
Posted by knechod
2nd Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
"Positive Train Control" is the idea of slowing trains down so they
pass each other without having to stop. You don't eliminate stops
for passenger ingress/egress. For that we'd need Heinlein's rolling
roads.
Posted by pranavb99@...
2nd Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
"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" - I think here is where the REAL savings are going to be made.

Exciting idea.
Posted by t0mmyt@...
3rd Sep 2010
+1 Vote
+ -
The laws of thermodyamics come into play
If it was economical to use batteries to store power during off-peak times and then release it during high-peak times, we'd be doing it already. It wouldn't take the excuse of a transit system to make it economical.

Besides, anybody familiar with the laws of thermodynamics knows that the energy saved when stopping the trains through regenerative braking is always less than the energy needed to get them going again. In other words, the battery will never have any excess energy to sell outside the transit system. It would help reduce the overall power consumption of the transit system, but as others pointed out this still may not be economical. However, it can't help the municipal power system overall unless the battery is over-engineered to store energy from the grid for later use -- but again if that was economical we'd be doing it already outside of the transit system.

For flywheel proponents, there's lot of issues in the implementation. To store energy most efficiently, they have to be run almost to the point of failure -- and when flywheels come apart the result is the same as an explosion. To reduce frictional loses, magnetic bearings have been looked at, but these require power to keep going and there's always the risk of power failure. But at least in this use, the flywheel is stationary and can be kept in a heavily reinforced building, and possibly run in a vacuum to reduce air friction.
Posted by zackers
4th Sep 2010
+1 Vote
+ -
RE: Philadelphia subway brakes for energy savings
Whose batteries is SEPTA using?
Posted by CazadorSiglo21
6th Sep 2010
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