BACK TO BASICS—HYDROGEN TRAINS What is a hydrogen train, and should we jump on the bandwagon?
Hydrogen fuel cells possess the possibility to transform power sources for many modes of transportation, including trains. Here is a primer about this exciting technology and the potential it holds for rail vehicles.
For the last decade or so, hydrogen has held out promise as an alternative fuel source that has the potential to both benefit the environment and beat diesel fuel in terms of energy efficiency. Hydrogen-drive technology, which has shown increasing improvements in efficiency and cost in the last several years, has slowly made its way from automobiles into larger modes of transportation, particularly in cases where batteries for electric power would be too large, heavy, costly, or otherwise impractical. Trains are just one of these modes of transportation; others include trucks, buses, ships, planes, and rockets.
How do hydrogen-powered trains work?
Hydrogen for trains works the same way it does in automobiles, trucks, buses, and ships; it’s used within fuel cells wherein a chemical process generates electricity, which is then used by an electric motor for locomotion. Specifically, hydrogen fuel cells are made up of an anode, a cathode, and an electrolyte membrane. Stored hydrogen passes through the anode, where it’s split into separate electrons and protons. The electrons (electricity) flow through a circuit and provide power, while the protons react with oxygen in the cathode and result in the waste product of water (expelled from the train as water vapor).
Fuel cells need a large supply of hydrogen, which is stored in a highly compressed form in high-pressure tanks for safety (like gasoline, hydrogen is extremely flammable and potentially explosive). Hydrogen-powered trains also use lithium batteries as supplementary power sources; these come with their own set of caveats (see Environmental Benefits, below).
Refueling of hydrogen trains
Trains powered by hydrogen are refueled from trackside containers whose supplies are delivered by truck, making these engine types inherently less efficient than those trains driven purely by electricity from overhead cables. As noted above, deliveries of hydrogen need to take safety into account and also the difficulty of handling compressed hydrogen; in this way, hydrogen is even more cumbersome to handle than gas or oil. In the future, hydrogen may need to be delivered in liquid form, which must be stored at extremely cold temperatures—another hurdle. For now, a robust fueling infrastructure for hydrogen does not exist for rail vehicles.
What are the benefits of hydrogen trains
Hydrogen-powered trains are better for the environment, more efficient than diesel-powered trains, and cost less to put into operation than the upgrading of rail lines that at present are not electrified.
Over the next decade, hydrogen-powered rolling stock and fueling infrastructure costs are expected to fall dramatically. Compared with electrified lines, there’s no roadwork disruption and/or utility relocation, so hydrogen-powered trains can potentially be implemented faster, with revenue captured earlier. Aesthetics and visual impact, particularly in urban areas, can be improved as no unsightly overhead lines and/or supporting infrastructure is required. Hydrogen-powered trains are a scalable solution as passenger numbers rise over time.
Hydrogen-powered trains are also quieter than their diesel-powered counterparts. Unlike electric trains, they are more resilient in the face of network-wide disruptions. “[Modern] shared electric infrastructure means that if there’s damage to [that] infrastructure, the operations of many trains on a line will be impacted,” explains Raphael Isaac, a rail fuel alternative researcher at the Railway Research and Education Center at Michigan State University.
Environmental impacts of hydrogen trains
The real benefit of hydrogen trains lies in the fact that they have zero emissions; however, that doesn’t mean that the entire lifecycle of hydrogen power is clean; it still takes energy to make the hydrogen in the first place. Today, most hydrogen is generated via the process of steam reformation—a method that’s neither clean (carbon monoxide and sometimes also carbon dioxide are waste products) nor highly energy-efficient (the process consumes and can also generate heat, which itself must be produced and/or dissipated).
The lithium batteries used by hydrogen power systems also come with environmental caveats. To mine one tonne of lithium takes 1.9 million liters of water, and lithium mining is detrimental to the environment in a number of ways. In the future, it may be possible to extract lithium from seawater, but for now, this is an experimental process.
Still, many hydrogen-powered trains are capable of operating as regular electric trains as well, so for sections of track that are electrified, there are opportunities for even greater energy efficiency. In the UK, the government has stated that it wants to eliminate all diesel trains by 2040. A number of governments around the world have set goals to be carbon-neutral by 2050, and hydrogen trains would help make progress toward this target.
Efficiency of hydrogen fuel-cell trains
The energy efficiency of hydrogen power derived from steam reformation is roughly 25 % to 35 %—which still beats diesel fuel, the energy-efficiency of which is approximately 20 %. To be more efficient, today’s hydrogen supplies would have to be derived via a different process—likely by electrolysis of water, whereby water is split into its hydrogen and oxygen components. So far, this process has only been successful in limited volumes.
However, even deriving hydrogen from water electrolysis still doesn’t beat electric power for efficiency—because it still needs to be processed before it can drive an electric motor, whereas electricity is already able to do this without any further processing. Also, electrolysis of water requires power to function. If the power for electrolysis could be generated from renewable sources like the sun or wind, this would be a sea-change in terms of efficiency, but this likely won’t come to pass without governments providing incentives to industry. Even if it did transpire, hydrogen still wouldn’t beat electric power that was renewably sourced in terms of energy efficiency.
How costly is the operation of hydrogen trains?
While it may seem that electric power—not hydrogen—can be most energy-efficient for trains, there’s much rail track in the world today (particularly in rural areas) that’s not electrified, and to electrify it could cost upwards of EUR1 million per mile for new infrastructure. By contrast, it’s much cheaper to convert or retrofit existing diesel-powered trains to run on hydrogen fuel sources; no infrastructure upgrades or conversions are necessary to accomplish this.
In Great Britain, only 42 % of rail networks are electrified, according to that nation’s Institution of Mechanical Engineers, meaning that the remaining 58 % can only be traversed by diesel-powered trains. In China, 72 % of rail networks are electrified, while in Europe, 55 % of rail networks are electrified, and in the United States, just 1 % of rail networks are electrified. All of these numbers translate to great opportunities for the implementation of hydrogen-powered trains.
“This is really the space where hydrogen fuel comes in as a cost-effective and valuable alternative and delivers a low-carbon railway,” declares Helen Simpson, an innovation and projects director at UK rail vehicle leasing firm Porterbook. “Where we’ve got all these long routes that don’t have as much passenger demand, the cost-benefit of electrifying the lines isn’t there.”
Still, hydrogen-powered trains are not cheap. The Alstom Coradia iLint (see below) costs approximately EUR5.86 million per train. Fortunately, however, operating costs are lower than those of diesel-powered trains because hydrogen is easy to produce.
“You can get it from renewable electricity, so with wind farms, solar farms, dams—anything that can generate electricity can generate hydrogen,” says Shawn Litster, a professor of mechanical engineering at Carnegie Mellon University. As mentioned previously, much hydrogen comes from steam reforming, so as Litster says, “there’s geographically a lot of flexibility around where you get the hydrogen from.”
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Hydrogen trains today
Hydrogen-powered trains are in their infancy; only a handful of models are in production and/or development worldwide. One issue with hydrogen is the space it takes up; even under compression, the efficiency per unit of volume is not as great as that of fossil fuels.
“While hydrogen has a lot of energy per mass—because it’s super light—it also takes up a lot of volume,” notes Michigan State University’s Raphael Isaac. “With our current hydrogen storage technologies, hydrogen takes up significantly more space than [equivalent] fossil fuels do.”
Countries with limited petroleum reserves such as Germany and Japan are good target countries for the adoption of hydrogen trains. The U.S., also, may be a good candidate for hydrogen trains as rail operator Amtrak could potentially replace all of its diesel engines with hydrogen vehicles as a way to go green; the U.S. already produces substantial amounts of hydrogen, a byproduct of American leadership in global natural gas production.
The Coradia iLint from Alstom is the world’s first hydrogen-powered train in commercial service. The regional iLint can travel at speeds up to 140 kph and boasts 965 kilometers of range on a single refueling, which is comparable to the range afforded by a single replenishment of diesel fuel. Two iLint trains are currently in service along a 100-kilometer corridor between German towns in the state of Lower Saxony. Alstom has a contract to build 14 additional iLint trains at a cost of EUR94.6 million.
Other German states have inquired with Alstom about hydrogen-powered trains for their regions, while France also hopes to have a hydrogen train up and running by 2022.
In addition to the iLint, in the UK, Alstom is retrofitting Greater Anglia Class 321 electric multiple-unit (EMU) regional trains to be hydrogen-powered, in association with the Eversholt Rail Group rolling stock leasing company. It’s planned that these converted trains, known as Breeze, or British Rail Class 600 units, will enter service in 2024.
Additionally, in the UK, Porterbrook—in association with researchers at the University of Birmingham—is developing the Hydroflex, another British train that will be powered by hydrogen. As of early 2020, the Hydroflex’s hydrogen fuel cells and power-generating equipment were installed in the middle of one of the train’s cars so that members of the public could view the technology (and accustom themselves to it operationally) in public demonstrations at the Quinton Rail Technology Centre at Long Marston, near Stratford-upon-Avon. Over time, the fuel cells and other apparatus of the Hydroflex will be installed under the rail carriages, rather than within them.
One limitation of the Hydroflex trains is that the trains have to be small enough to fit through Victorian-era railway tunnels in the UK. This limits the space for the hydrogen power system. The Hydroflex is designed to run for 80 to 120 kilometers along regional train routes. It’s projected that Hydroflex trains will be put into service commercially in the next two years after undergoing a lengthy testing and approval process.
Future opportunities and challenges
Certainly, from an environmental standpoint, hydrogen fuel-cell passenger trains are advantageous for many of the reasons outlined above.
But for freight as well, hydrogen trains present opportunities. In places like the U.S., where passenger trains are less popular, the ability to convert existing diesel freight trains to hydrogen power could make a case for mass-producing hydrogen fuel-cell engines. A recent report put out by the U.S. Department of Energy and the Federal Rail Administration noted that hydrogen-powered freight trains would have the “highest societal value,” despite being more technically challenging to produce. “The carbon writing is on the wall,” says Mike Muldoon, UK Head of Business Development at Alstom.
Still, freight is heavier than passengers, so more hydrogen (and the cold liquid form of the material) would be necessary to carry the same number of rail vehicles the same distance. At the University of Birmingham, engineers are researching more efficient ways to compress hydrogen. “There’s a huge challenge in terms of developing the infrastructure to supply the hydrogen to the railway,” said Stuart Hillmansen, one of the university’s professors and leader of the aforementioned Hydroflex project. “This technology exists, but there will need to be an uplift in the scale of these operations.”