Metro trains can sometimes generate energy when they brake, but right Metro doesn’t have a way to capture and use it. A recent WMATA study says the agency would need to buy less power from Pepco and Dominion if it installed battery systems along its rails.
In 2010, WMATA staff presented the idea for an “energy storage demonstration project” to the agency’s board of directors. Metro spends nearly $50 million dollars per year on power to make trains move, so any savings could be substantial. The study was performed and tested around 2013, but the FTA only recently published the results.
A brief background on train braking
Metro trains have two types of braking systems: dynamic and friction brakes. Dynamic braking on a train car is similar to what hybrid cars do when the driver steps on the brake: A motor turns when the brake pedal is pushed, and essentially acts as the brake to slow the car down while also generating an electrical current. That current gets fed back to the car’s battery, which lets you drive farther.
Dynamic braking is the focus of Metro’s demonstration project. When it’s used, the energy generated gets “dumped” back into the third rail, which is what transmits power for trains up and down the tracks. Usually, that energy put back into the system is lost and rendered useless, except when another train nearby is accelerating at the same time.
This is where batteries come in. Instead of wasting this energy, the testing system uses it to charge a large bank of batteries nearby. This energy can then be stored for a later time for when other trains are passing through and need to accelerate.
If Metro could save a significant amount of money with the battery system, then the agency could be able to pay less each year for electricity and put its money to better use elsewhere.
Credits – Stephen Repetski
Contributing Writer, Greater Greater Washington Magazine.