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SunTrain’s first real world test will be pushing clean power into Denver, past the congested powerlines surrounding the city. 

The Rocky Mountain state embraced SunTrain because its grid mirrors the nation’s. Power demand is up thanks to new data centers, incentives for building electrification and some of the U.S.’s strongest electric vehicle sales. Yet the state’s sclerotic grid means that every year utility company Xcel throws away more wind and solar generation. This happens when really sunny or windy days lead to generation outpacing transmission capacity. 

To meet rising demand and the state’s renewable energy goals, the state will need to invest as much as $8.7-billion more by 2045 according to the Colorado Electricity Transmission Authority. While that will inevitably mean many new overhead wires, SunTrain envisages its technology as a stopgap while those get planned and built. And when one part of the grid has been upgraded and power demands evolve, SunTrain can roll on to fix new bottlenecks. 

The 20-car battery trains envisioned for SunTrain’s Colorado pilot would shuttle between a pair of power plants. Most likely they would fill up with surplus energy from southeast Colorado’s solar plants at an Xcel power station in Pueblo, then travel roughly 240 kilometers on the Union Pacific Railroad to Denver, where the trains would release their power at a center-city power plant.

Jeff Anderson and Christopher Smith, SunTrain’s CEO and CTO, ticked through the work ahead as they walked me over to the company’s solar array at Pier 96 late last year, as an oddly sweet odor wafted through from the district’s meat processing plant. 

The cofounders, and still its only employees, make an interesting pair. Anderson is a serial entrepreneur and political junkie who has created and managed energy companies, trade groups and research consortia. Smith is an electrician who spent a decade with the International Brotherhood of Electrical Workers, facilitating $1.5-billion worth of wind and solar arrays, battery storage plants, and other energy projects. 

This year the duo hopes to complete their technology designs in collaboration with Xcel and the U.S. Department of Energy’s National Renewable Energy Laboratory, based in Golden, Colorado. One big task is automating the train-to-grid connection. SunTrain charges its demo car with hand-fastened cables that are similar to those attached to EV fast chargers. For the pilot, it needs to safely and speedily manage an order of magnitude more power. “The ability to have this operate as seamlessly as possible is really going to be key,” says Smith.

Smith opened his construction-grade laptop to show me competing designs for a fully-automated charging system. One extends robotic arms from a trackside installation to plug into each battery car, riffing off charging tech developed for electric buses, trucks and ferries by Swiss engineering firm Stäubli. (SunTrain wanted to show Stäubli’s robotic probe in action at the March demo, but thieves had made off with the rail car’s Stäubli socket). In another scheme, charging probes descend to each car’s battery containers from above. 

One task the company hopes it has already checked off is addressing worries about safety. Lithium ion batteries have caused fires in EVs, e-bikes and even Boeing’s 787 jets. Anderson says a recent 12-day transit from San Francisco to Denver was a start in reassuring railroads that its rolling batteries are different. “We proved that you can actually move power from one place to another and the batteries don’t shake to death. They don’t explode. Everyone’s still alive,” he says. 

SunTrain’s safety stems from its chosen flavor of lithium battery. Many consumer products and electric cars use lighter designs whose materials ignite relatively easily if they overheat. SunTrain, in contrast, uses inherently fire-resistant lithium iron phosphate batteries. Adding iron makes them heavier, but that’s not a problem for SunTrain. As Anderson notes: “Railroads are really good at moving heavy things.” 

It doesn’t hurt that railroads are experimenting with their own electric locomotives powered by massive batteries. EV engines should boost railroads’ comfort with batteries, and could eliminate SunTrain’s carbon footprint. The diesel locos in the Colorado pilot will add roughly 25 grams of carbon to every kilowatt hour of power delivered. While not ideal, that’s still 17.5 times cleaner than power from a plant burning natural gas. 

All this innovation doesn’t come cheap. SunTrain has raised over $3 million in venture capital, and Anderson says it needs another $12-15 million to build a test train. Xcel is seeking new funding to conduct the pilot after the U.S. Department of Energy’s Advanced Research Projects Agency passed on a $10 million research proposal in January.

As SunTrain and Xcel seek to put rolling power on the rails, a second transmission-boosting strategy to exploit the overlapping networks is already seeing its first deployments: threading new power lines through rail corridors. Utilities and independent transmission developers in New York and New England have completed small sections of power lines next to rail, with bigger projects in the works. 

“There’s potentially a drastic reduction in the need for clearing rights of way. To me that’s a huge win,” says Jacob Lucas, director of transmission system planning at New England utility Eversource. Co-locating power and rail is the right thing to do, he says, because doubling up the infrastructure protects natural spaces and communities from unnecessary disturbance.

Sharing railroads’ existing rights-of-way also avoids the burden of securing permissions from a multitude of landowners and government agencies. 

Lucas was involved in two recent projects that tapped rail corridors. One, in Connecticut, used several kilometers of Amtrak’s high-speed rail corridor near Hartford. Another, part of a joint venture with Danish offshore wind farm developer Ørsted, briefly hopped into the right-of-way for a Long Island commuter train to hook up New York’s South Fork offshore wind farm—the first large scale project of its kind in North America.

Lucas says that going trackside provided the fastest and least disruptive course. “Could we have found another route? Sure. But it would have been much longer. We would have been opening up more city streets, impacting other community stakeholders,” says Lucas.

Two bigger transmission projects in the works tap much longer stretches of rail property. The Champlain Hudson Power Express under construction to deliver Quebec hydropower to New York City follows tracks for over 200 kilometers. A bold project proposed for the Midwest, the SOO Green line, plans to follow rails for nearly all of its 560-kilometer journey from Iowa’s wind belt to Chicago.

There’s still resistance from railroaders to be overcome, since power transmission requires them to think differently about how they use their most valuable assets. Lucas thinks that’s why ‘colocation’ success stories remain few and far between, and even those were hard won: “In most of the cases I’m familiar with, it’s taken a lot of effort.”

But these early projects show that the railroading business can make space for cleaner energy when project developers make it worth their while. And railroads will have more motivation to sign on in the future. They still ship more fossil fuel than any other commodity, but much of that tonnage is coal, whose shipments have been falling for decades. 

If the railroads’ fossil fuel business continues that slide, it’s not hard to imagine them embracing clean power to fill the hole. And in so doing, they may just help American’s transmission ambitions get back on track.

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Peter Fairley is an independent journalist who has covered energy, technology, and the climate crisis for over two decades. His work appears in Scientific American, Technology Review, Discover, Nature, the Los Angeles Times, and other outlets.

Top image: ©Anthropocene Magazine