Siemens will begin working on the installation this fall at the Tacoma substation in southeast Portland, a spokeswoman told Railway Age.
Siemens spokesman Steffen Goeller says the "battery" is in fact a series of capacitors, designed to absorb energy when a light rail vehicle is braking and stopping, and then making the stored energy available to assist the vehicle's subsequent acceleration. Power is absorbed and released quickly, Goeller says.
"In this case there's the motor and when the train brakes, that braking energy is then fed back over the overhead wire into a stationary battery that sits on the wayside," Goeller said, noting the technology is already in use in China and in Spain.
TriMet notes the unit will allow TriMet to avoid placing a utility-connected substation in the same location. "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, in a statement.
Siemens is displaying the Sitras Energy Storage Unit at the annual American Public Transportation Association Rail Conference in Philadelphia.