Shipping solar power at the speed of a freight train
Electricity moves down a wire at close to the speed of light. In March, a tiny tech firm in San Francisco drew a crowd to witness power moving 100 million times slower, at the very modest pace of a freight train bumping around a rail yard. And I mean literally at freight speed, because the aptly-named startup, SunTrain, convened us to watch a diesel locomotive hauling solar energy.
The star of this demonstration at the Port of San Francisco’s Pier 96 rail yard was a freight container that SunTrain had crammed full of lithium ion batteries and mounted on a standard 27-meter railcar.
We watched as techs for SunTrain disconnected their battery-packed rail car from a trackside solar array. We watched a diesel engine push and pull the 50-ton battery car towards a parking lot 400 meters away. And then we saw a black Tesla sedan plug in to the rail car’s solar cargo.
To understand why 40 investors, regulators, and representatives from railroads, utilities and engineering firms braved a grey San Francisco morning to catch SunTrain’s odd power play, it helps to zoom out from Pier 96 and consider the state of the wires that zap electricity around the United States.
The U.S. power grid is congested, strains to reach far-flung solar and wind power resources, and will struggle to meet growing demand. According to the U.S. Department of Energy, the U.S. grid must double in size by 2050, but is currently expanding at an annual rate of just 1 percent.
SunTrain sees rolling batteries as the perfect workaround—a way to bypass the grid’s electrical disconnects and traffic jams. Imagine mile-long trains with 120 or more battery cars, charging up where wind and solar power is cheap and making daily deliveries of over two gigawatt-hours of clean energy each—enough to power a small city, port, or datacenter for days. A 2023 paper in Nature Energy found that moving charged batteries between regions could even help manage increasingly extreme weather events.
What grounds this vision is the fact that railroads mostly go where big power is needed. They feed almost all of the fuel for coal-fired power stations, deliver fuel rods to and from nuclear power plants, and supply giant transformers to the grid’s biggest switchyards.
SunTrain’s solution is one of several vying to turn America’s railroads—or their corridors of prime real estate—into grid solutions. If one or more proves as quick and cost-effective as they promise, railroads could help break the transmission logjams slowing renewable power’s roll-out across the country.