Wayside Energy Storage Project - Progress Update

July 15, 2011

Last summer, SEPTA partnered with Conshohocken (PA)-based smart grid firm Viridity Energy on implementing a new strategy to cost-effectively reduce SEPTA's energy consumption. SEPTA and Viridity applied for a grant from the Pennsylvania Energy Development Authority (PEDA) to pilot a "wayside energy storage" technology at a substation on the Market-Frankford Line in the Kensington Section of North Philadelphia. The energy storage device would capture, store, and reuse electricity generated from braking trains, improving energy efficiency and reducing demand along this important corridor.

With a $900,000 grant from PEDA in hand, the pilot project is now moving forward. After nearly one year, SEPTA and Viridity are in the process of planning its demonstration phase, which has received national recognition for its innovative integration of emerging smart grid technology with aging transit infrastructure. If successful, the project could have a potentially transformative impact on both industries.

Wayside Energy Storage 101

But first: what is wayside energy storage? And how does it work?

The concept of energy storage has, in fact, been around for some time. Hybrid-electric technology, for instance, improves vehicle fuel economy by coupling a diesel- or gasoline-fueled engine with an electric motor, which becomes an energy generator during braking. This so-called "regenerative braking" process creates energy that can be used immediately or stored in a battery. With this additional source of energy, hybrid-electric vehicles require less fuel-based energy. SEPTA's hybrid buses, for instance, are more than 20 percent more fuel efficient than their standard diesel counterparts.

Electrically powered trains also have regenerative braking capabilities. When trains brake, their electric motors produce energy - a six-car train can on the Market-Frankford Line produce up to three megawatts in 15 seconds of braking. The problem is, unlike hybrid vehicles, 20th century trains were not designed with an energy storage capacity. Regenerated energy from a braking train can be used if there is another train accelerating in the immediate area. Otherwise, the regenerated energy is wasted - dissipating as heat through resistor banks on the top of the train.

By installing an energy storage device at the Letterly Substation in Kensington, SEPTA will effectively "hybridize" a key portion of the Market-Frankford Line - its most heavily used service. The device will capture much of the regenerated energy, store it, and pump it back into the system as needed. In June, the project team selected Saft Batteries to manufacture the storage device and Envitech to supply the electronic controls for system integration. SEPTA anticipates that the device will supply approximately 10 percent of the power demand at Letterly, reducing electricity bills by more than $100,000. The demonstration phase is scheduled to begin this winter.

SEPTA's Letterly Substation in Kensington

While the energy storage device will save SEPTA money by reducing grid-based electricity demand, Viridity will work with the system to extend the project's benefits beyond just energy savings. By partnering with a smart grid service provider, SEPTA will be able to use its stored energy in markets as a "distributed energy resource." In so doing, Viridity will help SEPTA to maximize economic value. Viridity projects that the project will return more than $250,000 in total economic benefits - energy savings plus new market-based revenue.

The two markets from which Viridity anticipates revenue are referred to as "demand response" and "frequency regulation":

  • Demand Response: As a distributed energy resource, the storage device will enable load-shedding when marginal electricity prices are high - such as hot summer days. The device will also serve as a resource during emergency conditions. The Philadelphia region's grid provider, PJM, will provide compensation for these services. Plans are for the storage device to participate in the demand response market for two hours per day.
  • Frequency Regulation: To ensure a functional and reliable electrical grid, frequency must remain very close to 60 hertz (cycles per second). To achieve this stable frequency, the supply of electricity must exactly match demand. PJM continuously seeks this balance to maintain the proper frequency by increasing or decreasing small amounts of power output in response to minute-by-minute frequency deviations. SEPTA's storage device will effectively be "on call" to PJM for this regulation service, and will be compensated for its role in fine-tuning grid frequency. Plans are for the storage device to participate in the regulation market for 14 hours per day.

A Transformative Impact

The SEPTA-Viridity partnership has the potential to transform the way that the transit industry thinks about energy. Traditionally, transit agencies are among the largest regional energy consumers. In an era of rising energy prices, this puts the industry in a vulnerable financial position.

While transit, by its nature, will always be an energy intensive business, SEPTA's Wayside Energy Storage Project will demonstrate the extent to which some of that energy can be leveraged for financial benefit. For the first time, the project envisions energy as a two way street - SEPTA not only as energy consumer, but also as energy producer. In so doing, the project will not only result in economic and environmental benefits, but it will create an entirely new paradigm for the industry to formulate energy strategies.

The transformative value of this pilot project is in its scalability. For example: SEPTA has more than 30 transit substations serving the Broad Street Subway, Market Frankford Line, Trolleys, and Trackless Trolleys. While infrastructure constraints will limit energy storage application at all of these facilities, more widespread implementation of the technology could result in millions of dollars in economic and environmental benefits at SEPTA - a replicable model for energy savings and power optimization that can be deployed as a strategy to mitigate rising energy costs on transit systems nationwide.

SEPTA embraces its position of leadership and will be developing, analyzing, and disseminating data to demonstrate the pilot project's economic and environmental benefits to the industry and its stakeholders. SEPTA will also be applying lessons learned from the pilot project to fine-tune its approach to energy storage and seek out new funding opportunities to install additional devices. As a whole, SEPTA's energy storage initiatives will support its broader energy strategy, which is focused on achieving the sustainability program's goal of reducing energy intensity by 10 percent by 2015.