Caltrain Commissions 10-Megawatt Wayside Regenerative-Braking Battery Substation at San Jose Diridon Electric Terminal

Traction-power engineers with Caltrain and rail-electrification specialists from Stadler and the California State Transportation Agency commissioned a 10-megawatt / 7.5-megawatt-hour wayside regenerative-braking battery energy storage system (BESS) on Sunday afternoon at the San Jose Diridon Traction Power Facility at 65 Cahill Street in downtown San Jose. Serving the southern terminus of the 51-mile electrified corridor between San Francisco and San Jose, the high-cycle trackside storage plant captures kinetic braking energy from arriving seven-car Stadler KISS bilevel electric multiple-unit (EMU) trains and recycles it to launch departing northbound express trains.

Whenever an electrified Caltrain set decelerates from 79 mph into San Jose Diridon, its traction motors act as generators, feeding up to 4.2 megawatts of 25-kilovolt AC electricity back into the overhead contact wire. If no nearby train is accelerating on the same electrical sector at that exact second, excess catenary voltage previously had to be curtailed or exported back through utility transformers.

Wired directly across the 25-kV autotransformer bus via solid-state silicon-carbide bidirectional inverters, the six liquid-cooled lithium-titanate (LTO) battery containers absorb full-power regenerative braking pulses in less than 10 milliseconds and rated for 25,000 deep charge cycles. Moments later, when two northbound trains accelerate simultaneously out of Diridon platforms, the wayside battery discharges up to 10 megawatts into the catenary, cutting peak utility demand charges from San Jose Clean Energy by 38 percent and providing fifteen minutes of emergency station-clearing traction power during a grid outage.

The $14.2 million wayside energy recovery project was funded through California Transit and Intercity Rail Capital Program (TIRCP) grants. Riders can view electric train schedules on the Caltrain Official Portal.