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Mass Transit Operator Provides Frequency Regulation with Battery Storage

The Southeastern Pennsylvania Transportation Authority (SEPTA), which operates mass transit in the Philadelphia region, announced construction of a second system to recover and store braking train energy as electricity. Similar to a pilot system installed in 2012, this system will transfer electricity to batteries and bid this electricity into PJM Interconnection’s electricity frequency market.

Key Details

  • Energy is transferred from trains stopped at nearby stations to an energy storage system located behind the meter at a substation along the Market-Frankford Line
  • Stored energy can be used by SEPTA to operate trains or delivered to the grid for frequency regulation
  • PJM manages a 700-MW frequency regulation market that sends fast and slow signals to market participants; SEPTA participates in the fast market which is designed for battery storage systems
  • In the first four weeks of January 2014, SEPTA made more than $47,000 in the frequency regulation market
  • The second system adds super capacitors, which will allow the battery to stay in the frequency regulation market more consistently; this change raises SEPTA’s reliability metrics and allows it to earn more money
  • Additional benefits of the new systems include recovering more braking energy and extending the battery life
  • The project is supported by a $1.4-million grant from the Federal Transit Authority


Spurred by technological advances and supportive regulations, companies are deploying innovative solutions that bring value—beyond energy—to the electric grid. In this instance, PJM was the first grid operator to receive approval for rules responding to FERC Order 755. This order requires RTOs and ISOs to develop methods to compensate technologies, such as storage systems, that can provide frequency response more quickly than conventional generators. ScottMadden expects these market rules will spur continued storage advancements and growth in PJM. In December 2013, SNL reported 270 MW of storage was under construction or being studied in the PJM interconnection queue.

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Contributing Authors

Paul Quinlan Clean Tech Manager

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