A train can send power back to the grid when it brakes, and Caltrain now gets paid for it

A train can send power back to the grid when it brakes

A train can send power back to the grid when it brakes, and one transit agency now gets paid for doing it every day. Regenerative braking works by running the electric motors of a train backward during a stop, turning them into generators that push current back through the wires instead of drawing power from them. Caltrain, the commuter railroad that runs the length of the San Francisco peninsula, runs an entirely electric line, and about 23% of the electricity used on that line comes back from trains braking, according to the agency. Starting in April 2026, the 2 power providers for Caltrain will pay the agency about 1 million dollars a year under a new billing arrangement called the Net Billing Rate, which credits the agency for electricity trains send back to the grid.

And now with the new regenerative braking, their cleaner, quieter and more efficient travel will send even more emission-free power back to the larger regional grid.

Shawn Marshall, chief executive officer of Peninsula Clean Energy, one of the 2 power providers involved. Source 1.

Caltrain first estimated 19.5 million dollars a year in electricity cost, then revised that figure down to 15.3 million dollars once a full year of actual electric service usage was measured.

How much power the wider research says a train can return

A peer reviewed review of the engineering, published in IEEE Transactions on Intelligent Transportation Systems, found that a reversible substation, equipment that sends braking power back into the main alternating current grid instead of turning it into heat, can typically return up to 13% of the energy a train consumes. The same review found 2 other methods that keep braking energy inside the rail system rather than sending it to the public grid. Storing energy onboard a train or beside the tracks can save about 30%. Timing trains so one speeds up as another brakes nearby can save between 4% and 34.5%. The review studied metro and tram systems where stations sit close together, unlike the longer, faster stretches between stops on the peninsula. That difference in how the trains operate is why the 23% figure and the 13% figure describe 2 different kinds of systems, not 1 correcting the other.

A pending bill in California would add more

Assembly Bill 1372, written by Assemblymember Diane Papan with Senator Scott Wiener as a coauthor, was introduced on February 21, 2025, and amended on January 5, 2026. It remains pending and is not yet law. The bill requires the responsible utility to credit a transit agency for exported electricity based on avoided cost, the price a utility would otherwise pay to produce or buy that same electricity. Caltrain says passage would add a further 20% in compensation from Pacific Gas and Electric, on top of the 1 million dollars a year already secured under the Net Billing Rate.

I'm pleased to see that the renewable energy that Caltrain is sending back to the grid is being recognized and fairly compensated.

Diane Papan, the assemblymember who authored Assembly Bill 1372. Source 1.

Philadelphia banks the energy instead of exporting it

SEPTA, the transit agency in the Philadelphia region, takes a different, older path. Rather than exporting metered electricity the way Caltrain does, SEPTA stores braking energy in batteries at substations, the equipment connecting the rail line to the wider grid, then sells grid stabilizing services from that stored energy to PJM Interconnection, the regional grid operator, for up to 200,000 dollars a year. The first installation opened in 2011 in North Philadelphia with a grant from the Pennsylvania Energy Development Authority and cut demand at that substation by 20%. The storage network has since grown to 7 installations totaling 8.75 megawatts, financed through a 20 year battery services agreement with Constellation.