Powering down: A new project will harness energy from subway trains like this one on Philadelphia’s Market-Frankford Line.
SEPTA
A battery will capture power from braking trains.
The Southeastern Pennsylvania Transportation Authority (SEPTA), which runs the transit system in Philadelphia, is piloting a smart electrical grid technology that could cut its electricity bills by up to 40 percent and generate millions of dollars a year.
A massive battery installed at one of the authority's substations will store electricity generated by the braking systems on trains (as the trains slow down the wheels drive generators). The battery will help trains accelerate, cutting power consumption, and will also provide extra power that can be sold back to the regional power grid. The pilot project, which involves one of 38 substations in the transit system, is expected to bring in $500,000 a year. This figure would multiply if the batteries are installed at other substations.
The project shows how cash-strapped public transit agencies that operate major subways and electric rail systems could find a new source of income by tapping into the smart grid. It also highlights one way that the smart grid could save energy, avoid blackouts, and incorporate more renewable power.
Several energy utilities are already experimenting with using large batteries to help smooth out fluctuations in electricity supply, keeping the grid operating at the correct frequency and preventing blackouts. In the new pilot project, this kind of battery technology will be paired with software from a Philadelphia-based smart grid company called Viridity Energy.
The software will decide how to allocate the power stored in the battery, using it to drive trains and smooth out spikes in SEPTA's power distribution network. SEPTA could also sell the excess power to various electricity markets, depending on a number of factors, including what's most profitable.
The pilot project, which Viridity expects to complete by next summer, will make use of the regenerative braking capabilities of Philadelphia's subway trains. These systems convert kinetic energy into electricity as the train slows down. In the existing system, without the battery, that power can be sent back into SEPTA's power distribution system and used to help another train accelerate--but only if it happens to be accelerating at the same time the power is generated, says Laurie Actman, director of government relations and business development at Viridity. Otherwise that power is lost.
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"That power can already be sent back into SEPTA's power distribution system and used to help another train accelerate--but only if it happens to be accelerating at the same time the power is generated, says Laurie Actman, director of government relations and business development at Viridity. Otherwise that power is lost."
It took me two reads to _assume_ that the author meant the power is lost -- by SEPTA, but not lost altogether. This is the power that is sold back to the grid at large.
Also, the title of this article is a bit deceptive. It should be something more like "Subway Trains to Reclaim Wasted Energy".
Sorry for the confusion. I'll make a change to try to clarify. She's referring the the current set-up, before the new Viridity system is installed.
I think they are trying to use the same battery to do brake/accelerate for subways and frequency correction for the grid.
Presumably, the battery is only used for brake/accelerate some of the time (say 1 minute every 4 or 5) and is available for frequency correction for the rest of the time.
Why don't they use flywheels for this, it might work better than batteries for the large power and short time requirements.
(+ some supercaps to smooth it further).
I can't see that they will have extra energy to sell to the grid, just some capacity for frequency correction.
Re: Braking or time shifting ?
Yes, it seems to me that the energy storage issue/solution for train power is the same as that for the grid, and would be better to be placed on the shared grid instead of single-use train grid.
If the battery, flywheel, etc. energy stabilization storage is placed on the grid and the train net is bidirectionally connected to the grid, then that storage system could be used for other power fluctuations, not just train loads and regeneration.
The trains add peaks and valleys to the grid load not "on-demand" but when the trains need to accelerate or decelerate. However, the times are somewhat predictable with a good train control system, and could be used to control the energy storage level in anticipation of demand/supply.
In the same vein, having a solar carport to charge an EV only doesn't make sense (except at a remote off-grid location) because the solar panels are not used when a car is not charging. Put the panels on the grid and the car charger on the grid, then you can use one without the other with full utilization.
Guest
great idea should be installed in all trains though.
The Hybrid Electric Kinetic Photovoltaic Vehicle
Trains have been reclaiming electricity during braking and putting back into the grid for decades. France since the 1960s or 70s; and, as the first commentary notes, Finland too. All over the world. Does this transit agency not have a net-metering pricing arrangement and therefore buys and sells power at different rates? Or something else?
Batteries are currently an extraordinarily expensive form of storing grid energy. There must be something missing here. Otherwise, the most economical thing to do is simply put the power back into the grid and let some other party use it while that train slows down. Furthermore the fluctuations on the grid created by trains accelerating and decelerating are tiny blips in an urban grid, so load balancing doesn't justify either...
Why not put the batteries or super capacitors in a central location of the subway power network?
No need to load the trains with batteries and the power generated by braking trains can be stored , time schedule independent, to be used for accelerating trains
Hi! I read your article and I wrote something about it at http://bit.ly/d2GWke
thank you
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tate0774
4 Comments
Energy recovery in trains
Feeding electrical energy from the braking of metro trains back to the grid has been advantageously used in the metro of Helsinki, Finland, since the 1970's. The system was designed and delivered by ABB.
No batteries are required in an AC network.
In my humble opinion,
Taisto Leinonen, M.Sc.
Helsinki, Finland
Reply