Saft’s Li-ion batteries help save 10% on energy bills with train braking

Name of Project:
Saft’s Li-ion batteries help save 10% on energy bills with train braking
Philadelphia, PA  
Renewable Integration  
Southeastern Pennsylvania Transportation Authority  
Viridity Energy, ABB’s Envitech Energy  


Saft’s premium lithium-ion (Li-ion) technology was an ideal solution for Southeastern Pennsylvania Transportation Authority’s (SEPTA) challenge to capture energy from braking trains. A first-of-its-kind endeavor, turns train brakes into generators delivering a 10 percent savings on energy bills. SEPTA runs the public transport system for the city of Philadelphia and its surrounding area, serving 3.9 million. SEPTA was looking for a way to both make the most of its operating budget and boost its green credentials. SEPTA is located in the operating area of PJM, a regional transmission operator that has opened its frequency regulation market to non-traditional resources. This prompted SEPTA to take an innovative approach to use the world’s first system to capture the kinetic energy of braking trains and store it in a large-scale battery system.


Combining Saft’s Intensium® Max 20P Li-ion energy storage system with Viridity Energy’s optimizing system and ABB group’s Envitech Energy’s system, the project aimed to provide a greener and more efficient public transport system. For this pilot program, the battery storage system was required to capture the braking energy of trains at five stations on one of SEPTA’s busiest routes, the Market-Frankford line. On an average working day, each of the five stations experience 400 stopping trains, enough to generate more than 1,200MWh every year. Saft used its energy storage expertise to design, install and commission an Intensium Max® 20P system to meet the exact project specifications. A standardized 20-foot containerized system houses Saft’s Synerion® 24 Li-ion battery modules, power conditioning, communications interface, battery management and cooling and fire prevention systems. The energy storage system unit (ESSU) is formed by 29 modules in series and the container has 10 ESSU’s in parallel. Coupled with Saft’s well-proven reliable and maintenance-free Li-ion technology, the system has a 20-year design life with 1.5MW peak charge and discharge power. It also has 420kWh storage capacity.


Saft played a vital role in meeting SEPTA’s main objectives for the storage asset, including reducing the grid energy consumed (1,050-2,100MWh pa), capturing market-based revenue such as frequency regulation and providing power ‘insurance’ in case of an emergency outage. Regenerative breaking now enables SEPTA to recover an average of 1.1MWh on weekdays and 1.5MWh at weekends. The impact of SEPTA’s system reduces CO2 emissions by more than 1,000 tons pa, SO2 emissions by more than 5 tons pa, NOx emissions by more than 1 ton pa and mercury emissions by more than 22kg pa. The impact of the system saves 2-4kWh per event and 1,057-2.115MWh pa. Supply savings are approximately $95-$190K pa with a market revenue potential of $75-250k pa. This puts the total economic benefit at $170-440k pa.

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