Oregon’s upcoming TriMet Portland-Milwaukie light rail system line will be one of the first in the nation designed to capture heat energy from braking trains and convert it into electricity that can be used to power other trains accelerating in different parts of the system.
The Siemens Sitras SES system that’s set to be installed in the trains doesn’t work with batteries like other hybrid trains, though. It uses a massive supercapacitor to store the recaptured energy that would, otherwise, be lost as heat during braking. The proposed supercapacitor is able to quickly absorb and release energy, which will help the system to meet ever-changing power demand and reduce the frequent voltage peaks commuter trains experience under acceleration. If multiple trains are accelerating at the same time (which happens at rush hour all across the city) the voltage demands could exceeds the available supply of electric power – which is what’s currently happening at peak hours and the primary problem the Siemens system was built to address.
While the KERS trains are already in use across Europe, the Portland TriMet system is set to be the first application of the Siemens Sitras SES system in the US. In Philadelphia, though, there is a similar regenerative braking system mounted to the trains running on the Market-Frankford line which sends braking energy “back down the third rail” to an array of batteries. There, the transit authority, uses some of that power, and sells the rest of it back to local utilities. Siemens’ supercapacitors are due to be installed on the TriMet trains this October, with the TriMet’s 7.9-mile Portland-Milwaukie line is scheduled to open in 2015. No word, yet, on who gets the system next. I hope it’s Chicago!