How hydrogen ​‘e-fuels’ can power big ships and planes

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Airplanes and cargo ships guzzle staggering amounts of oil as they soar across the sky and ply the ocean, resulting in significant planet-warming emissions every year. Several low- and zero-carbon alternatives are emerging that could replace all that dirty petroleum. Making the switch, however, will require using staggering amounts of a different commodity: clean hydrogen.

Fuels derived from hydrogen — including e-methanol, ammonia and e-kerosene — are considered essential to decarbonizing the jets and freighters that carry heavy loads over long distances. Today’s batteries can’t provide enough power without weighing these giant vehicles down — that technology is better suited for cars, trucks, ferries and even smaller planes. Biofuels from crops and waste can fuel planes and ships, but the world probably can’t produce enough to meet all the future demand.

Hydrogen-based fuels, by contrast, pack more energy per volume than batteries or even hydrogen alone. And, unlike with biofuels, the ingredients needed to make these alternatives to petroleum are virtually unlimited.

As momentum grows to decarbonize the trickiest parts of the economy, the aviation and global shipping sectors are moving to turn this hydrogen-infused promise into a reality. No commercial jets and only a handful of cargo ships use so-called ​“e-fuels” today. But companies and governments worldwide are investing billions of dollars to develop new engines, fuel systems and safety protocols to support the rollout of cleaner-burning transportation fuels.

The big question is whether the fuels themselves will be available in sufficient quantities when ships and jets are ready for them.

“It has become clear that the only fuels that are actually sustainable long-term and scalable are going to be hydrogen-derived,” said Aoife O’Leary, founder and CEO of Opportunity Green, a U.K.-based organization.

“If you want to have that sustainable fuel, it really means building out this [supply] infrastructure now,” she said. For that reason, the environmental nonprofit launched a coalition last year with hydrogen-focused startups to advocate for policies and programs that boost H₂ use across the skies and seas.

To make e-fuels, clean (or ​“green”) hydrogen must first be produced with electrolyzers, which split water molecules into H₂ and oxygen. That hydrogen is then combined with other elements, such as nitrogen or carbon dioxide, through energy-intensive processes. In order to deliver the steepest emissions reductions, all of those steps must be powered by clean energy.

Today, however, nearly all the world’s hydrogen is produced from fossil gas using highly carbon-emitting methods. That means an enormous buildout of renewable energy and electrolyzer capacity is required to not only replace existing dirty hydrogen but also expand overall production to serve new customers, including ships and planes.

Achieving just a 10 percent share of e-fuels in both aviation and shipping by 2030 could trigger around 2,100 terawatt-hours per year of additional renewable electricity demand, according to the Paris-based International Energy Agency (IEA). That’s the size of about half of the annual electricity consumption in the United States.

To make enough clean hydrogen to reach that 10 percent target, the industries would need to build 400 gigawatts in total electrolyzer capacity — equal to the entire global pipeline for electrolyzer projects from now to 2030, the IEA said in a December report. There’s little time to wait, given that it can take up to a decade to build green hydrogen projects over 1 GW.

Installing all of that renewable energy and electrolyzer capacity will require billions of dollars and years of planning and permitting. The task appears all the more daunting when considering that other industries are clamoring for the same resources. Electricity providers need massive amounts of wind and solar energy to decarbonize the power grid and charge battery-powered vehicles. Producers of steel, chemicals and fertilizer also plan to use plenty of clean hydrogen to curb their own outsize CO₂ emissions.

Given the future competition, O’Leary and other experts say they’re worried that, unless companies start investing in e-fuel projects now, shipping and aviation won’t secure enough clean hydrogen to help meet global targets for slashing greenhouse gas emissions. A key concern is that the limited hydrogen supply will go toward applications — such as residential heating and light-duty vehicles — that have other viable ways to decarbonize, instead of to the sectors that need it most.

“There’s a risk that heavy transportation sectors might end up in a place where they realize they don’t have a good solution [for decarbonization],” said Emily Kent, the U.S. director of zero-carbon fuels for the Clean Air Task Force.

“That would leave some of those sectors unabated, and potentially not be compatible with the carbon-neutral world we’re aiming for by 2050,” she added.

Shipping goods with ​“future fuels”

Aviation and shipping each face their own unique set of challenges in decarbonizing their globe-trotting fleets with e-fuels. Let’s start with the big ships.

The global shipping industry is responsible for about 3 percent of the world’s annual greenhouse gas emissions. Most of that climate pollution comes from vessels that burn diesel in massive engines as they haul trillions of dollars’ worth of goods around the globe.

In 2023, the United Nations agency that governs international shipping set new, stricter targets for reducing emissions from ocean-crossing freighters starting in 2030. And this January, the European Union began regulating maritime-related emissions under its cap-and-trade system, which requires that cargo ships buy credits for every metric ton of CO₂ they produce within the region. (Airplanes joined the system in 2012.)

Both policies are starting to steer shipping companies toward adopting two hydrogen-derived fuels in particular: e-methanol and green ammonia.

“We absolutely need these future fuels to get to around net-zero [emissions] in 2050,” said Roger Holm, president of Wärtsilä Marine, a Finnish engine and technology developer. 

Methanol (CH₃OH) is considered a potential near-term replacement for diesel. The ubiquitous chemical is used to produce everything from paints and plastics to cosmetics and car parts. The colorless liquid can work as a ​“drop-in” maritime fuel if relatively minor adjustments are made to ship engines and fuel systems. Methanol doesn’t produce harmful soot or particulate matter when burned, and it can deliver deep reductions in CO₂ emissions when made from renewables.

As is the case with hydrogen, most methanol today is produced from fossil fuels. But alternative versions exist. ​“Bio-methanol,” the most common type, can be made using crop waste or other organic materials, which are then rendered into a synthetic gas that’s processed in a reactor. ​“E-methanol” comes from combining clean hydrogen with carbon dioxide — the latter of which can be captured from the exhaust fumes of power plants or, potentially, pulled from the sky using direct air capture.

When produced that way, e-methanol can have a relatively tiny ​“well-to-wake” emissions footprint, according to a 2021 analysis. Still, burning any kind of methanol results in CO₂ emissions, since the compound contains carbon atoms.

Ammonia, meanwhile, is predicted to become the leading fuel source for big ships in the long run. The carbon-free compound (NH₃) is mainly used in fertilizer, plastics and cleaning products; right now, nearly all of it is made using fossil fuels in highly energy- and carbon-intensive processes. But it’s possible to use only renewables to both produce and synthesize hydrogen and nitrogen to make ​“green” ammonia.

The industry has a long way to go before it’s launching fleets of ammonia-powered ships. The chemical is highly toxic and corrosive, and extensive safety measures are required for handling and storing it. Ammonia-powered engines and fuel cells are still in the early stages of development, though Wärtsilä introduced the industry’s first commercially available ammonia engine last fall.

By contrast, nearly two dozen vessels already run on conventional methanol. As of July 2023, shipping companies had placed orders for over 150 methanol-powered tankers and container ships — a tiny fraction of the roughly 50,000 merchant ships that move cargo internationally today, but significant growth all the same.

Last year, Danish shipping giant Maersk signed the industry’s first large-scale supply agreement for green methanol — including both bio- and e-methanol — with the Chinese wind-turbine maker Goldwind. The contract calls for 500,000 metric tons per year of methanol, which requires about 100,000 metric tons of clean hydrogen to make, according to BloombergNEF.

Holm said such offtake contracts are essential for resolving the ​“chicken-and-egg” paradox that’s plaguing the production of green shipping fuels. Fuel producers are reluctant to invest in large facilities if they can’t guarantee customers for their cleaner but more expensive products. At the same time, shipping companies are hesitant to buy or build new types of vessels until they’re sure enough e-fuels will be available at manageable prices.

Flying high with hydrogen

Airlines are, well, in the same boat when it comes to creating a clean-hydrogen supply chain from scratch.

“There are customers who are naturally cautious of moving, and there are customers who have a vision of early decarbonization,” said Peter Jones, director of green hydrogen for Scottish Power. In January, the energy company partnered with U.S. startup ZeroAvia to begin exploring the idea of developing hydrogen infrastructure for airports, using electrolyzers backed by U.K. wind farms.

“The most important thing is to get real projects and deliver real hydrogen to real customers and get the experience out there in the market,” he said.

Global air travel contributes about 2 percent of the world’s annual energy-related CO₂ emissions, though flying may actually be responsible for 4 percent of total global warming when condensation trails and other non-CO₂ factors are taken into account.

In 2022, nations reached a milestone agreement to achieve ​“net-zero” emissions from the world’s airplanes by 2050. To date, the vast majority of the industry’s efforts to achieve that goal have focused on boosting supplies of sustainable aviation fuel, or SAF. These are lower-carbon fuels that can be used as ​“drop-in” substitutes for fossil fuels in existing jet engines and fuel-supply systems.

Today, SAF represents less than 0.1 percent of total global aviation fuel. Most of the current supply is made by rendering used cooking oil and animal fats into biofuels, with the rest made from corn stalks, forest residues and other types of biomass. Yet these materials may all become limited or prohibitively expensive as demand grows from heavy-duty trucking, shipping and other sectors.

A 2022 report from the Clean Air Task Force found that U.S. biofuel production would need to more than double over the coming decades to meet just the domestic aviation sector’s energy demand, potentially taking up more and more land and exacerbating food insecurity in the process.

“We know that we’re going to have to develop and deploy other types of fuels to decarbonize the aviation sector, and that those fuels are going to be hydrogen-rich,” said Jonathan Lewis, the task force’s director of transportation decarbonization and a co-author of the biofuels report.

Smaller regional aircraft may be able to use hydrogen directly, by flowing H₂ gas over a fuel-cell system. Last year, ZeroAvia and the startup Universal Hydrogen began test-flying propeller planes equipped with fuel cells over the English countryside and the U.S. West Coast, respectively. Yet researchers say that barring a breakthrough, the technology can’t produce enough power to fly the industry’s heaviest emitters: large long-distance aircraft.

Instead, big planes could burn ​“e-kerosene,” an emerging alternative to bio-based SAF. The fuel, also called ​“power-to-liquid” fuel, can be produced using clean hydrogen, captured carbon dioxide, heat and lots of electricity — ideally all from renewable sources.

A growing number of startups are working to develop and scale the highly energy-intensive process, which they claim can deliver life-cycle emission reductions of around 90 to 97 percent compared to petroleum-based kerosene. Burning the e-fuel in engines still results in CO₂ emissions. But producers say their goal is to reduce net emissions from jet fuel by repurposing CO₂ that would’ve otherwise wound up in the atmosphere.

Only a handful of relatively small operations currently produce e-kerosene worldwide, and there are a lot of unknowns about how well larger facilities will perform economically, or how environmentally beneficial the fuel will ultimately be. Recent projections from the International Civil Aviation Organization reflect this ambiguity. According to the U.N. body, e-fuels could account for between 3 and 17 percent of aviation fuel by 2035, and between 8 and 55 percent by 2050, depending on how technologies and policies develop.

What’s certain, however, is that any e-kerosene producer will need to get its hands on copious amounts of clean hydrogen — which in turn requires installing copious renewable energy. The same can be said for all the e-fuels now in development.

Consider the flight path between New York City’s John F. Kennedy Airport and London’s Heathrow Airport. The Clean Air Task Force estimated that, if all 25 daily roundtrip flights were powered by e-fuels, that would require building a facility the size of the Neom Green Hydrogen Complex — an $8.4 billion ​“mega-plant” in Saudi Arabia that will integrate 4 GW of solar and wind energy to produce up to 600 metric tons per day of hydrogen.

Jones of Scottish Power said the next decade will be especially crucial for scaling renewable energy capacity to meet the expected hydrogen demand from ships, planes and other sectors working to decarbonize in the coming years.

“Without that renewable buildout, there’s only a limited place that hydrogen can go,” he said.

Verdagy manufactures an advanced AWE electrolyzer system that has superior performance to almost any system in the market — high current densities and the largest membranes leading to higher hydrogen production, high efficiencies leading to lower LCOH, and wide dynamic range and fast turndowns to seamlessly integrate with renewables. In addition to its Silicon Valley factory, Verdagy operates its R&D and highly automated commercial pilot plants in Moss Landing, California, where it continues to advance its cutting-edge technology.