Energy Storage for the Rail Industry, Part I: Onboard or Wayside Systems?
April 02, 2018 | Alpbora Oruc, Sr. Sales Applications Engineer
Cleaner, greener, emissions-free transportation is a worldwide trend. The automotive industry has the most pressure to quickly innovate and deploy more environmentally-friendly technologies, but the rail industry is feeling that pressure as well. Regulations surrounding carbon dioxide reductions impels rail operators to electrify and adopt technologies that support emission reduction.
As the rail industry travels in the direction of renewable energy, Europe is seeing fuel cell trains replace traditional diesel trains and more miles of track are becoming electrified. Energy storage systems provide a solution to the challenges of electrification and efficient energy management. There are two approaches for rail energy storage that have significant advantages for cost savings and operational efficiency: wayside energy storage and onboard energy storage.
Wayside Rail Energy Storage
In traditional rail systems without energy storage capability, excess energy is lost when a train brakes. The problem is that overhead rail lines are not able to recover excess energy and provide it back into the grid. When the train brakes, there are voltage peaks on the line, and that voltage has to burn off in resistors in order to protect the electrical equipment from damage. This burned energy is lost as heat—imagine the accrual of energy as trains stop and start throughout the days, weeks and months, and the potential of all this extra energy to be put to good use!
This is where energy storage becomes a game-changer. A wayside rail energy storage system is a stationary system that can be installed at a specific location on the overhead (catenary) line that is connected to the line by an inverter. The energy storage system captures and stores the train’s braking energy so that it can reuse that energy at a later time.
Energy storage installed on a rail system can capture excess energy produced when the train brakes and dispatch that energy back into the grid for use at a later time, helping to significantly reduce energy consumption and support emissions reduction.
With energy storage installed as part of the rail system, when the train brakes, the excess energy produced is captured by the energy storage and dispatched back into the grid for use at a later time when the next train pulls power from the line. The energy storage system is typically placed at substations and near areas where there is repeated braking and starting.
Generally speaking, the application of energy storage results in approximately 20 percent energy cost reduction.1 The cost savings manifest for the operator of the overhead lines.
Onboard Rail Energy Storage
Onboard energy storage is installed on the train itself. The advantage of onboard energy storage is that the train is not dependent on proximity to substations to access the extra energy the storage system provides. The dramatic reduction of the peak power demand due to boost- and recuperation-power from ultracapacitors results in considerable benefits for the infrastructure, which may even enable a reduction of substations on a line. This is the best option for rail operators who want to save energy and protect the overhead lines or electric components onboard with respect to high voltage and low voltage fluctuations. Onboard energy storage is also used for hybrid trains to reduce fuel consumption via using the recuperated energy and running the diesel at more efficient operating points. Diesel trains further benefit from onboard energy storage for a reliable and compact engine starting system operating down to –40°C.
Choosing a wayside or onboard energy storage approach depends on the train and how often fluctuations occur on the line. If there is a substation with high usage in a city center, stationary wayside energy storage makes the most sense. In the case of historical city centers where no overhead lines are desired, an onboard solution will enable catenary-free operation with substation charging as well. For trains that travel through remote locations or that have a diesel-electric traction system, onboard energy storage is a more efficient strategy.
Next week in Part II of this blog post, I’ll discuss the benefits of ultracapacitor energy storage for specific rail applications.
1 Maxwell Technologies’ wayside ultracapacitor energy storage system solution for the Southeastern Pennsylvania Transportation Authority light rail system resulted in the reduction of the rail vehicles’ consumption of grid-supplied electrical energy by 10-20%. See case study for more details.
Sr. Sales Applications Engineer
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