SFMTA Commissions 8-Megawatt Battery-Buffered 600-Volt DC Trolleybus Substation at Potrero Yard to Power Hill-Climbing Electric Coaches

Traction-power engineers with the San Francisco Municipal Transportation Agency (SFMTA) and clean-grid specialists from the San Francisco Public Utilities Commission (SFPUC) commissioned an 8-megawatt / 6.4-megawatt-hour stationary lithium-iron-phosphate (LFP) battery-buffered 600-volt DC traction substation on Sunday afternoon at the Potrero Bus Yard at 2500 Mariposa Street (at Bryant Street) in San Francisco's Mission and Potrero district. Supporting North America's largest zero-emission overhead electric trolleybus network, the solid-state DC substation powers heavily ridden 60-foot articulated New Flyer XT60 coaches climbing steep grades along the 14-Mission, 22-Fillmore, and 30-Stockton corridors.

When multiple sixty-foot articulated trolleybuses accelerate simultaneously up an 18-percent San Francisco grade while also in-motion-charging their onboard off-wire auxiliary batteries, localized voltage drops along legacy 600-volt DC copper feeder cables previously triggered traction-breaker trips. Conversely, coaches descending Potrero Hill and Castro Street generate surges of regenerative braking current along the twin overhead contact wires.

Connected directly to the 600-volt DC feeder bus via bidirectional silicon-carbide DC-DC converters, the Potrero Yard stationary battery bank—built from repurposed, safety-recertified transit battery modules—absorbs downhill braking surges with 94 percent round-trip efficiency and injects instantaneous current support whenever feeder voltage dips below 565 volts DC. During an earthquake or neighborhood PG&E feeder outage, the 6.4-MWh buffer keeps hill-climbing trolleybus routes operating for up to two hours on 100 percent renewable Hetch Hetchy Power.

The $9.4 million traction-power upgrade was funded through Federal Transit Administration Bus and Bus Facilities grants and California Low Carbon Transit Operations Program funds. Bay Area riders can view Muni electric fleet details and route schedules on the SFMTA Official Portal.