Are hydrogen-powered vehicles a realistic path to clean energy? It’ll take years to know.

Every morning at a transit facility in Canton, Ohio, more than a dozen buses pull up to a fueling station before fanning out to their routes in the city south of Cleveland.

The buses — made by El Dorado National and owned by the Stark Area Regional Transit Authority — look like any others. But they reflect the cutting edge of a technology that could play a key role in producing cleaner inter-city transportation.

In place of pollution-belching diesel fuel, one-fourth of the agency’s buses run on hydrogen. They emit nothing but harmless water vapor.

Hydrogen — the most abundant element in the universe — increasingly is viewed, along with electric vehicles, as a key way to slow the environmentally destructive impact of the planet’s 1.2 billion vehicles, most which burn gasoline and diesel fuel.

Manufacturers of large trucks and commercial vehicles are beginning to embrace hydrogen fuel cell technologies as a way forward. So are manufacturers of passenger vehicles, planes and trains.

Transportation is the single biggest U.S. contributor to climate change. That’s why hydrogen power is seen as a potentially important way — not today but in the long run — to help reduce carbon emissions.

For now, though, the hydrogen that’s produced is mainly for refineries and fertilizer manufacturing and is made using natural gas or coal. That process pollutes the air, warming the planet rather than saving it. A new study by researchers from Cornell and Stanford universities found that most hydrogen production emits carbon dioxide, which means hydrogen-fueled transportation can’t yet be considered clean energy.

Yet proponents of hydrogen-powered transportation say hydrogen production is destined to become more environmentally safe. They envision a growing use of electricity from wind and solar energy, which can separate hydrogen and oxygen in water. As such renewable forms of energy gain broader use, hydrogen production should become a cleaner and less expensive process.

Within three years, General Motors, Navistar and the trucking firm J.B. Hunt plan to build fueling stations and run hydrogen trucks on several U.S. expressways. Toyota, Kenworth and the Port of Los Angeles have begun testing hydrogen trucks to haul goods from ships to warehouses.

Volvo Trucks, Daimler Trucks AG and other manufacturers have announced partnerships, too, aiming to offer zero-emissions trucks that save money and meet stricter pollution regulations.

In Germany, a hydrogen-powered train began operating in 2018, and more are coming. France-based Airbus, the world’s largest manufacturer of planes for airliners, is considering hydrogen as well.

Hydrogen fuel is included in President Joe Biden’s plans to cut emissions in half by 2030. The infrastructure bill the Senate has approved includes $9 billion for research to reduce the cost of making clean hydrogen, and for regional hydrogen manufacturing hubs.

About 7,500 hydrogen fuel cell cars are on the road in the United States, mostly in California. Toyota, Honda and Hyundai produce the cars, which are priced thousands more than gas-powered vehicles. California has 45 public fueling stations, with more planned or under construction.

“This is about the closest I’ve seen us get so far to that real turning point,” said Shawn Litster, a mechanical engineering professor at Carnegie Mellon University who has studied hydrogen fuel cells for nearly two decades.

Hydrogen has been running some vehicles for years. Around 35,000 forklifts in the United States — about 4% of the nation’s total — are powered by hydrogen. I

Craig Scott, Toyota’s head of advanced technology in North America, says the company is maybe two years from having a hydrogen truck ready for sale. Building more fueling stations will be crucial to widespread adoption.

Tony Dejak / AP

Kirt Conrad, chief executive officer of Canton’s transit authority since 2009, says other transit systems have shown so much interest in the technology that SARTA takes its buses around the country for demonstrations. Canton’s system, which bought its first three hydrogen buses in 2016, has added 11 more and built a fueling station.

“We’ve demonstrated that our buses are reliable and cost-efficient, and as a result, we’re breaking down barriers that have slowed wider adoption of the technology,” Conrad said.

Two California transit systems, in Oakland and Riverside County, have hydrogen buses in their fleets.

The Port of Los Angeles began a hydrogen test in April, when the first of five semi-trucks with Toyota hydrogen powertrains began hauling freight to warehouses in Ontario, California, about 60 miles away. The $82.5 million public-private project eventually will have 10 semis.

The long-haul trucking industry appears to be the best bet for early adoption of hydrogen. Fuel cells, which convert hydrogen gas into electricity, provide a longer range than battery-electric trucks, fare better in cold weather and can be refueled much faster than electric batteries can be recharged. Proponents say the short refueling time for hydrogen vehicles gives them an edge over electric vehicles for use in delivery trucks or taxis, which are in constant use.

That advantage was important for London-based Green Tomato Cars, which uses 60 hydrogen fuel cell-powered Toyota Mirai cars in its 500-car zero-emission fleet to transport corporate customers. Co-founder Jonny Goldstone said his drivers can travel more than 300 miles on a tank and refuel in three minutes.

Because drivers’ earnings depend on fares, Goldstone said,

“if they have to spend 40, 50 minutes, an hour, two hours plugging a car in in in the middle of the working day, that, for them, is just not acceptable,” Goldstone said.

Green Tomato is among the largest operators of hydrogen vehicles in what’s still a tiny market in Europe, with about 2,000 fuel cell cars, garbage trucks and delivery vans.

Unlike with buses and heavy trucks, experts say the future of passenger vehicles in the United States lies mainly with electric battery power, not hydrogen. Fully electric vehicles can travel farther than most people need to go on a relatively small battery.

The world now produces about 75 million tons a year of hydrogen, but most of it is from carbon emission-creating processes involving steam reformation of natural gas. China uses higher-polluting coal.

So-called “blue” hydrogen, made from natural gas, requires an additional step. Carbon dioxide emitted in the process is sent below the Earth’s surface for storage. The Cornell and Stanford study found that manufacturing blue hydrogen emitted 20% more carbon than burning natural gas or coal for heat.

That’s why industry researchers are focused on electrolysis, which uses electricity to separate hydrogen and oxygen in water. Hydrogen mixes with oxygen in a vehicle’s fuel cell to produce power.

The amount of electricity generated worldwide by wind and solar is growing, making electrolysis cleaner and cheaper, said Joe Cargnelli, director of hydrogen technologies for Cummins, which makes electrolyzers and fuel cell power systems.

For now, it costs more to make a hydrogen truck and produce the fuel than to put a diesel-powered truck on the road. Hydrogen costs about $13 a kilogram in California, and one kilogram can deliver slightly more energy than a gallon of diesel fuel — which costs around $3.25 a gallon.

“As they scale up the technology for production, the hydrogen should come down,” Litster said.

While a diesel semi can cost around $150,000 depending on how it’s equipped, it’s unclear how much fuel cell trucks would cost. Nikola, a startup electric and hydrogen fuel cell truck maker, estimated last year it would get about $235,000 for each hydrogen semi it sells.

Clean electricity eventually might be used to make and store hydrogen at a rail yard, where it could refuel locomotives and semis, all with zero emissions.

Cummins foresees the widespread use of hydrogen in the United States. by 2030, sped by stricter diesel emissions regulations and government zero-emissions vehicle requirements.

Europe has set ambitious green hydrogen targets designed to accelerate its use.

“That’s just going to blow the market open and kind of drive it,” Cargnelli said. “Then, you’ll see other places like North America kind of follow suit.”