Caltrain Commissions 4-Megawatt-Hour Wayside Battery Substation at San Jose Diridon to Store Electric Train Braking Power

Traction power engineers with Caltrain and energy storage specialists from San José Clean Energy commissioned a 4-megawatt-hour wayside lithium-iron-phosphate (LFP) battery energy storage substation on Saturday evening along the southern throat of San Jose Diridon Station at 65 Cahill Street in San Jose. Connected through a solid-state step-down transformer to the 25-kilovolt, 60-hertz overhead contact system (OCS) along the 51-mile electrified San Francisco-to-San Jose rail corridor, the wayside storage bank captures high-power regenerative braking bursts from arriving seven-car Stadler KISS electric multiple-unit (EMU) trainsets.

Whenever an electric Caltrain decelerates from 79 miles per hour into Diridon, Santa Clara, or Sunnyvale stations, its traction motors act as generators that feed up to 3.2 megawatts of electricity back into the overhead catenary wire. During off-peak evening and weekend windows when no nearby train is accelerating in the same electrical section to absorb that current, voltage limiters previously curtailed a portion of the regenerated energy. The new Cahill Street battery bank absorbs those 45-second braking surges at 94 percent round-trip efficiency and discharges the stored energy minutes later as northbound trains accelerate toward San Francisco.

Across daily revenue service, the wayside battery cuts peak 15-minute utility demand charges at the San Jose traction substation by 31 percent, saves an estimated 2.6 gigawatt-hours of grid electricity annually, and provides fifteen minutes of emergency station-approach movement power if a local utility feeder trips.

The $5.2 million rail energy-storage project was funded through a California State Transportation Agency Transit and Intercity Rail Capital Program (TIRCP) grant. Riders can view electrified train schedules and sustainability reports on the Caltrain Electrification Portal.