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Portland Light Rail Captures Energy From Brakes

Leon Walker

Maxwell Technologies is supplying ultracapacitors for an energy-saving braking energy recuperation system that American Maglev Technology, is installing on light rail vehicles operated by the Portland, Ore., area’s TriMet transit authority.

TriMet won a $4.2 million grant from the US Department of Transportation’s Federal Transit Administration Transit Investment for Greenhouse Gas and Energy Reduction, or TIGGER, program to improve the efficiency of its fleet of 101 light rail vehicles equipped with regenerative braking after determining that the vehicles were able to use only about 70 percent of the energy generated by braking.

In regenerative braking systems, the electric motor that propels an electric or hybrid vehicle also does most of the braking. When the brakes are applied, instead of employing a conventional friction-based braking process, the system signals the electric motor to run in reverse mode, creating resistance to slow the vehicle. An electric motor running backwards also acts as an electric energy generator or dynamo that converts the kinetic energy of motion into electrical energy that can be stored for reuse, improving efficiency.

In TriMet’s system, energy generated by decelerating vehicles is fed into the traction electrification system for use by other vehicles on the system. TriMet is using the TIGGER funding to retrofit 27 vehicles with the American Maglev-designed, ultracapacitor-based, energy storage system, which captures and stores regenerative braking energy as it is generated, uses the stored energy for acceleration, and releases surplus energy to other vehicles on the system as needed. The 27 retrofitted vehicles are being paired with non-capacitor equipped vehicles so that stored energy can be used by both vehicles.

To measure and validate anticipated energy savings, TriMet will compare in-service energy consumption data collected by on-board vehicle propulsion computers before and after the retrofit.  According to a bulletin published by the FTA and prepared by the US Department of Energy’s National Renewable Energy Laboratory, preliminary data collected by TriMet indicate that the roof-mounted ultracapacitor-based energy storage systems will result in annual energy savings of approximately 2.8 percent.

In November, engineers from Stony Brook University in New York announced that they had invented a technology for harvesting energy from the vibration of railroads that can be used to help railroad companies save millions in energy costs. The team developed an energy harvester that converts the irregular, oscillatory motion of train-induced rail track vibrations into regular, unidirectional motion, in the same way that an electric voltage rectifier converts AC voltage into DC. The system could save more than $10 million in trackside power supply costs for railroads in New York State alone, along with a reduction of 3,000 tons per year of CO2 and a half million dollars of electricity savings, the team estimates.

Do you work at a transit authority? What energy saving techniques has your organization implemented? Please tell us in the comments section below.



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