The Tri-County Metropolitan Transportation District of Oregon (TriMet) is improving the energy efficiency of its light-rail fleet with a $4.2 million TIGGER Program grant.

TriMet operates a fleet of 127 light-rail vehicles, 101 of which feature regenerative braking—upon deceleration, the vehicle motors function as generators and make power available to the traction electrification system. However, TriMet studies indicate that only 70% of this regenerated power is captured and used by nearby light-rail trains. When no trains are near, the remaining 30% of the regenerated power is lost.

To remedy this energy loss, American Maglev Technology will install double-layer capacitor units on 20 light-rail vehicles in the TriMet fleet. The air-cooled capacitor units will release previously stored electrical energy upon acceleration, thus using nearly 100% of the regenerated power captured from braking trains.

The capacitor-equipped vehicles will be paired with non-capacitor-equipped vehicles so that the captured energy can be used to accelerate both vehicles. The maximum energy storage capacity of each roof-mounted capacitor unit is about 1 kWh, which should be sufficient for accelerating a vehicle to 25 mph and operating it for about 2,500 feet on level track. In addition to capturing energy and reducing peak-load demand, these capacitor units reduce power substation loads and allow the light-rail system to grow in train density without installing additional substations.

The capacitor units feature a high level of efficiency, an extremely dynamic charge-transfer capacity, excellent cycle strength, and a long (15 year) service life.