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Clean Transport high-speed train in taiwan

Published on June 5th, 2013 | by Nicholas Brown

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Siemens Installing America’s First Regenerative Energy Storage Unit

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June 5th, 2013 by  

Siemens, a German manufacturer of a wide variety of items (you could consider it Germany’s GE), is installing a regenerative braking energy storage system for the new TriMet Portland-Milwaukie Light Rail Transit Line, a first in the US.

high-speed train in taiwan

Photo Credit: 棟樑‧Harry‧黃基峰‧Taiwan (CC BY-NC 2.0 license)



It is the Sitras Energy Storage unit and is powered by ultracapacitors (sometimes called supercapacitors or EDLCs). Ultracapacitors are very heavy, but they can provide massive bursts of power very quickly, and that is desirable for acceleration of light rail transit at times.

This system will operate by capturing the kinetic energy possessed by the light rail train while it is braking to help slow it down and also generate electricity, which is then stored by the mentioned energy storage system.

The energy storage system will then power the light rail train when it is accelerating. Powering the train with an energy storage system during acceleration prevents the massive power consumption spike caused acceleration, providing a form of voltage stabilization.

These power consumption spikes cause a phenomenon called “voltage sag,” or a “voltage drop.”

When you draw current from any power source, it causes the voltage to decrease. The extent of that is determined by the amount of current drawn relative to the amount of current it is designed to provide.

Due to the fact that other trains are sometimes connected to the same power sources, they can cause power disruptions if too many of them simultaneously accelerate due to excessive voltage sag, causing the voltage to drop below the required level.

Finally, this regenerative braking system improves energy efficiency. “The regenerative energy storage unit is an important piece of the many sustainable elements being incorporated in this light rail project,” said Dan Blocher, executive director of TriMet Capital Projects. “With Siemens as a partner, we know this pilot project is positioned to bring a new and efficient technology to the U.S.”

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About the Author

writes on CleanTechnica, Gas2, Kleef&Co, and Green Building Elements. He has a keen interest in physics-intensive topics such as electricity generation, refrigeration and air conditioning technology, energy storage, and geography. His website is: Kompulsa.com.



  • Corbin Holland

    lukedog69 is correct…. septa did this years ago sorry to burst your bubble nicolas

  • Peter

    Another system to consider for train systems is gravitional potential energy. It is a perfect fit for trains since trains the majority of brake and acceleration is near the stations. eg Vitoria subway line in London: “The line has hump-backed stations to allow trains to store gravitational potential energy as they slow down and release it when they leave a station, providing an energy saving of 5% and making the trains run 9% faster. http://en.wikipedia.org/wiki/Victoria_line

  • lukedog69

    this is not a first. there is a similar system on the subway in phila. done by viridty and SEPTA.

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