Mind the (Hydrogen) Gaps

Written by Michael Iden, P.E., Contributing Editor and Consultant, Tier 5 Locomotive LLC
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The California Energy Commission in late 2022 awarded a $4 million grant to Sierra Northern Railway for the design, integration and demonstration of a hydrogen fuel cell (HFC) switching locomotive.

RAILWAY AGE, JULY 2023 ISSUE: Hydrogen is getting significant attention as a future energy source for railroads, but are all the pros and cons being recognized and discussed?

Railroad decarbonization (eliminating locomotive emissions of carbon dioxide, CO2) and energy efficiency are not always, and often cannot be, synonymous. Railroading’s classic metric for “fuel efficiency” (U.S. gallons fuel/thousand gross ton-miles) is becoming a bit “fuzzy” because alternative fuels have different energy densities. Three separate gallons each of B20 biodiesel blend, R90-B20 bio/renewable blend and petroleum diesel have different amounts of energy. 

Remember that one definition of energy is “the ability to do work” (such as moving freight trains). “Cleaner fuels” (usually with less volumetric energy) often result in using more physical volume of fuel (although the total energy used may be the same). I discussed the dual challenge of rail decarbonization and competitive energy efficiency three years ago during a UIUC seminar (“Decarbonization & Energy Efficiency: The Dual Challenge for U.S. Freight Railroads,” University of Illinois Urbana-Champaign, Hay Railroad Engineering Seminar, June 4, 2021; https://railtec.illinois.edu/wp/wp-content/uploads/2021_06_04-Mike-Iden_Hay-Seminar.pdf)

Regarding “green” hydrogen (made entirely from tomorrow’s “green” renewable electricity generation and transmission network) can be zero carbon, achieving the decarbonization goal, but at the cost of consuming large amounts of electricity, some of which is lost to process inefficiency. The process of disassociating (breaking down) deionized water into hydrogen and oxygen is called electrolysis. All hydrogen must be “manufactured” because it doesn’t exist freely on our planet; electrolysis is likely the best process for zero carbon. Keep in mind that a national plan for decarbonization means investing $1 trillion for large increases in renewable generation and a modernized power grid.

Hydrogen then must be “packaged,” either by liquefaction or compression (both of which require more energy), to make it transportable in hydrogen energy tenders (high technology “locomotive appurtenances,” not tank cars). Some amount of hydrogen will always be lost to leaks, so add more efficiency losses. In fuel cells, the hydrogen is recombined with atmospheric oxygen, releasing electrons to produce electrical power for the locomotive traction motors, but again there are more efficiency losses. 

This gives us four (4) “energy conversion processes” in transforming hydrogen in water into an “energy carrier” of propulsion electricity. Let’s calculate the power grid-to-rails energy efficiency:

  • Efficiency of electrolysis to “manufacture” H2 from water: 67%.
  • Efficiency of H2 compression/liquefaction: 90%.
  • Efficiency of fuel cells combining H2 and O2, producing electricity: 60%.
  • Efficiency of inverters and traction motors powering locomotive wheels: 95%.

All these combined to produce “at the rails” energy efficiency is 34% for hydrogen, meaning we ultimately and irreversibly lose 65% of the “clean” renewable electrical energy that went into electrolysis at the beginning. To produce 1 megawatt-hour (MWh) of electrical energy from onboard H2 fuel cells to produce work at the rails, we need 2.94 megawatt-hours of renewable electricity powering the electrolysis. Math check: 1 MWh of energy for “work at the rails” divided by 2.94 MWh input energy for electrolysis equals 0.34, or 34%.

Key point: Hydrogen and fuel cells may be a good solution for replacing diesel locomotives and their emissions, but at a significant “energy cost.” Given that all-battery locomotives are unlikely to have suitable operating range except in special applications (like downhill mine-to-port railroads recovering exceptionally heavy amounts of cyclical dynamic braking energy) hydrogen may be better than batteries for line-haul propulsion.  

But should hydrogen be used universally across the entire freight rail network? The numbers, in my opinion, suggest “not.”

Good decision-making for any “megaproject” (defined as any project with an investment exceeding $1 billion) includes complete assessment of reasonable alternatives. This means performing multi-faceted analyses (safety; economics, including risks and return on investment; operating expenses; impact on operations, customers, the environment) to rank alternative solutions. By the way, using public data, what rail assets can be acquired for $1 billion in capex? One billion dollars will get you 300+ Tier 4 diesel freight locomotives, or 200 battery-electric switching locomotives with charging infrastructure (“Follow the Megawatt Hours: Hydrogen Fuel Cells, Batteries and Electric Propulsion,” Railway Age, March 2023; https://www.railwayage.com/mechanical/locomotives/follow-the-megawatt-hours-hydrogen-fuel-cells-batteries-and-electric-propulsion/).

What about hydrogen infrastructure? Even though it’s unlikely railroads would invest in their own electrolysis plants for making hydrogen, investors will be required to fund them, and they will demand an economic return (especially factoring in their own cost of input electricity). The current “world’s largest” hydrogen plant is being built in China to produce 30,000 metric tons (30 million kilograms) of H2, the energy equivalent of approximately 30 million gallons of diesel fuel, for US$831 million using Chinese material and labor. Thirty million gallons of diesel replaced is barely 1% of U.S. freight railroads’ total annual diesel consumption. 

This brings me to selective freight main line electrification—selective as in high-density freight corridors. Discussions usually go “flat line” when electrification is mentioned, but no unbiased comparative analyses of electrification vs. hydrogen fuel cell propulsion have been published. 

Electrification’s “at the rails” energy efficiency compared to hydrogen shows
the difference:

  • Efficiency of grid energy to and at the overhead catenary: 90%.
  • Efficiency of inverters & traction motors powering locomotive wheels: 95%.

Combined, these produce “at the rails” energy efficiency of 86% for electrification.

To have 1 MWh of energy for work at the rails using electrification, we need 1.17 MWh upstream feeding the catenary. Math check: 1 MWh of energy for “work at the rails” divided by 1.17 MWh supplied to the substations and catenary equals 0.86, or 86%.

Where would hydrogen’s energy efficiency disadvantage be most pronounced? On the 7%-10% of U.S. freight route-miles that do 30% of the industry’s work, a sub-network of four to six long-distance Class I corridors. One such corridor, BNSF’s Transcon, stretches from Chicago to Los Angeles and requires upwards of 1,200 diesel locomotives operating at any time along its 2,000 route-miles. This corridor using hydrogen would consume 151% more electricity (2.94 MWh electrical energy for 1.00 MWh energy used at the rails) compared to electrification (1.17 MWh electrical energy for 1.00 MWh energy used at the rails). Hydrogen and electrification can both decarbonize this corridor, but the comparative energy efficiencies are startlingly different. Again, the dual challenge: On the 70% of the national network below highest density, hydrogen may be the best (and only) solution.

A classic argument against electrification has always been “we cannot tolerate having dedicated locomotives.” Because any conversion to hydrogen will likely take years (a decade or longer?), H2 locomotives and tenders will initially be dedicated to specific corridors (unlike today’s “go anywhere” diesel-electric locomotives). And unless, and until, sufficient H2 production, storage and “refueling” infrastructure is built and commissioned along our example corridor, end-to-end operation of H2 locomotives and tenders using mostly H2 for energy will become a protracted year-by-year zone-by-zone implementation. Electrification would be a similar year-by-year implementation, although my article in March 2023 Railway Age discusses an alternative approach that facilitates quicker operation under emissions-free catenary and even allows “segmented and discontinuous” electrification.

Biodiesel blends will likely be railroads’ best alternative to petroleum diesel because renewable diesel may never reach production levels needed to satisfy every user’s demand for energy (freight railroads consume ~3 billion gallons per year; heavy-duty trucks ~40 billion). And the marketplace for “cleaner” fuels will become even more challenging and competitive as Sustainable Aviation Fuel (SAF) starts flowing to commercial aviation.

My thinking about “H2 engines” or H2-ICE (internal combustion engines) using diesel-plus-hydrogen) is “time will tell.” I don’t believe it has been proven that a large-bore medium-speed diesel engine can be successfully modified to burn diesel and hydrogen without producing some emissions like NOx. It is too early to proclaim H2-ICE will produce only water (like a fuel cell). And we don’t yet know the thermal efficiency (energy in vs. energy out).

Fuel cell locomotives are experimental, and the required hydrogen infrastructure doesn’t yet exist. The industry needs many experimental fuel cell locomotives, energy tenders and reasonably large volumes of hydrogen infrastructure to assess long-term safety, reliability, maintainability and life-cycle costs, none of which are known. Extrapolating “results” from stationary fuel cells or low-power transit buses or light-rail passenger trains is risky at best. Because hydrogen is a highly flammable gas (even more so than methane, the main constituent in natural gas), our typical diesel locomotive shop will be unsuited to allow any locomotive containing even residual amounts of hydrogen inside the building.

What about “hydrogen hubs” to be funded under the federal Inflation Reduction Act as part of the Department of Energy’s “Regional Clean Hydrogen Hubs” program? Does this “open the gate” for hydrogen locomotives? Again, consider the numbers: $7 billion in federal funds will allow construction of 6 to 10 hydrogen-producing centers across the U.S. What is unclear, however, is just how much hydrogen will be produced when all the yet-to-be-selected proposals are funded, designed, built, commissioned and placed in operation. And keep in mind the “world’s largest” hydrogen facility mentioned earlier, in China. The “published facts” and numbers don’t make me optimistic that rail can count on significant progress toward hydrogen by depending on hydrogen hubs.

Anticipative exuberance about hydrogen for railroad propulsion (using fuel cell or H2-ICE locomotives) is warranted, but it must be tempered and combined with cautious technical, operating and economic optimism. The largest use of hydrogen today is by refineries producing gasoline, involving stationary equipment and only 1,600 miles of specially built hydrogen pipelines (compared to 190,000 miles of petroleum and 305,000 miles of natural gas pipelines).

What world-class entity has the largest experience using hydrogen in mobile applications? NASA. Suggested reading: “Of Hydrogen and Humility,” The Space Review, September 6, 2022.  Even if liquefied hydrogen is never used by railroads, the paper’s last statement is important: “[I]it may be wise to temper that confidence seen earlier with the recognition that even tried-and-true technologies pose challenges—with more, perhaps, yet to come.”  

SEE ALSO: Hydrogen: Hope or Hype?