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SEPTA, Constellation, and Viridity Energy to deploy 8.75MW energy storage system to capture and reuse subway train braking energy

An 8.75MW battery storage network which will capture and reuse the energy created by braking subway cars will help Southeastern Pennsylvania Transportation Authority (SEPTA) reduce operating costs, ensure energy resiliency, and support the stability of the electrical grid.

Constellation, a subsidiary of Exelon Corporation, will fund, own, and operate the 8.75MW battery storage network, deployed at seven SEPTA substations. The network is designed to use stored energy to power trains as they accelerate from stations and can provide emergency generation for trains in the event of a power outage. ABB will provide engineering, procurement, construction and operations services to Constellation for the project. Saft will provide the lithium-ion battery technology.


Recovery and reuse of braking energy is well proven and is now widely used in hybrid electric vehicles and, more recently, by bus operators the world over. The solution installed by SEPTA is based on ABB’s Envistore Regenerative Energy Storage System, which usually uses capacitors to store braking energy and release it again shortly afterwards to boost train acceleration.

For SEPTA’s application, the capacitors were replaced with high performance Saft Intensium Max20P Li-ion battery systems. The Max20P system, packaged in 20-foot containers, comprises Saft Synerion 24 Li-ion battery modules, power conditioning, communications interface, battery management, cooling and fire prevention systems.

The energy recovery and storage system is complemented with software that enables SEPTA to monitor energy prices and sell the stored energy back to the grid when energy prices are high, usually during peak hours and in hot weather, so helping reduce operational costs and creating a new revenue stream.

An expansion of SEPTA’s 1.8 MW battery storage pilot program completed in 2014, the new network brings the agency’s total battery storage capacity to more than 10 MW. The pilot recovered an average 1.1 MWh on weekdays and 1.5 MWh on weekends.

The expansion project, which is among the first commercially deployed battery storage systems in a transit operation, requires no upfront capital investment from SEPTA and will be financed through a 20-year battery services agreement with Constellation.

As a competitive energy supplier, we aim to provide our customers with the best long-term economic and business solutions for how their energy is produced and supplied. This battery storage network, along with $26 million in guaranteed savings from efficiency improvements Constellation is implementing for SEPTA, will help SEPTA deliver on its budget and energy resiliency goals.

—Gary Fromer, senior vice president of distributed energy at Constellation

The stored energy will help to balance electric load on the PJM Interconnection, the regional transmission organization that manages the movement of wholesale electricity in 13 states and the District of Columbia. Viridity Energy will provide energy market services for the project, bidding the batteries into the PJM market as frequency regulation resources to help match generation with demand and maintain the desired electrical frequency on the grid.

Construction activities are scheduled to begin in the second quarter of 2016 with estimated commercial operation in late 2016.


Henry Gibson

Sodium Nickel Chloride cells are much more robust and are not the danger of fires such as was demonstrated in several toys this winter with lithium batteries. The many tiny cells and their interconnections of lithium batteries will always be a high cost and reliability issue. Large very high energy and very high power sodium cells can be built for large batteries with many fewer connections.

The sodium sulphur batteries from NGK have had their fire potential solved and are much cheaper than any form of lithium battery and need no expensive cooling systems at any outside temperature cold or hot. The nickel chloride systems have very much longer lives with almost no maintenance required and can remain operating with the standard type of failure of its cells if they happen. Weight is of little concern since these batteries are stationary. If very high instant power is required this can be met by the commercially available buried flywheels. If there are any third rail or low voltage catenary installations in this system, the Chloride batteries can be directly connected to the conductors. The Sodium Nickel Chloride batteries are light enough to be carried in all rail vehicle for regeneration, and the lightweight flywheels demonstrated by Ricardo and others are also lightweight enough for very high power braking and regeneration in every rail vehicle in combination with the Chloride batteries. Ricardo, Artemis and Bombardier are already developing on board regeneration for diesel powered rail vehicles.

Certainly, very large battery systems should be a part of every electric rail system, and they should be built with low cost, long life, low maintenance, reliable, and safe cells and only the Sodium Sulphur and Sodium Nickel batteries meet all of these requirements. SoNick batteries are already used in Europe for reliable lighting in rail vehicles and they are also the right voltage for homes long before Tesla.

Electric rail systems should also meet their responsibility for low carbon reliable electricity, and install low maintenance micro-turbines throughout their systems where natural gas is available. The waste heat can be used for cooling or heating buildings. The use of heat, even waste heat from turbines, has been used for over a century and has been much improved over the years. It can even produce ice that can be stored for later use. Co-generation is now the cleanest and cheapest and fastest and lowest cost way to reduce carbon release in the present developed world. Such machines can be brought into operation to meet demand as required for trains or grid supplement. They can supply third-rail voltages directly if necessary or better can charge, directly, batteries directly connected to the third rail. In some cases, it would be suitable to use combined cycle systems with perhaps standard geothermal equipment for additional electric generation prior to other uses of waste heat. Properly made and connected steam boiler turbine generators can supply power peaks for a few seconds several times their continuous capacity and could be a valuable part of a larger combined cycle unit. Commercial compressed air turbine units were made in the past for backup UPS systems for power whilst diesel generators were started.

Energy storage in batteries can multiply the energy cost by a factor of two or more. ..HG..

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