Hydrogen: A Misguided Path for Future Aviation Fuel
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Chapter 1: Overview of Hydrogen in Aviation
This week, I engaged in a thought-provoking discussion about the role of hydrogen as a fuel for aviation. A master's thesis candidate organized a panel of specialists, and I had the pleasure of serving as the "It ain't gonna fly" voice, contrasting with others who were more optimistic about hydrogen’s possibilities.
The conversation spanned a wide range of topics, including safety, technical aspects, economics, and airport operations. While I have previously published various viewpoints on these concerns, I had yet to consolidate them into a cohesive argument. The framework laid out by the researcher offered an excellent opportunity to unify my main objections to hydrogen in aviation, drawing from my publications, dialogues with experts worldwide, and my involvement with electric aviation advisory boards.
The researcher is pursuing a Master of Science in Airport Planning and Management at Cranfield University, a well-regarded institution in the UK’s aerospace sector. Founded in 1946 as the College of Aeronautics, Cranfield has evolved into a premier postgraduate research facility. Notably, the Rolls-Royce University Technology Centre (UTC) at Cranfield, established in 1998, showcases the collaboration between British aerospace giant Rolls Royce and the university. The UK Aerospace Technology Institute (ATI), also based at Cranfield, drives the technology strategy for the UK aerospace industry and funds top-tier research and development.
It’s worth noting that FLIMAX, the electric aviation startup I advise, has connections to Cranfield, highlighting its significance in the aerospace startup ecosystem. The panel I participated in included a diverse group: a senior lecturer in air transport, a sustainability expert from a global consultancy involved in the UK ATI FlyZero study, and a professor with decades of experience in hydrogen combustion engines.
As I shared with the panel, I was somewhat of an outsider—I do not work full-time in aviation or aerospace and do not hold a senior research position in this field. Instead, my input stemmed from an independent projection I created regarding aviation decarbonization through 2100. While it is merely a scenario, it is multifaceted and based on a thorough evaluation of various transport sectors, including ground, maritime, and air.
Chapter 2: Economic Viability of Hydrogen
Let’s delve into the comprehensive analysis of hydrogen's potential for aviation, starting with its economic aspects.
Hydrogen production costs are a critical consideration. I have previously published evaluations of the expenses associated with producing green and blue hydrogen. My analysis of European initiatives aimed at sourcing hydrogen from northern Africa revealed that while hydrogen can be produced sustainably, it is unlikely to be affordable.
For instance, a review of a halted project by Equinor, Air Liquide, and Eviny to establish a Norwegian liquid hydrogen facility for maritime applications suggested that production costs could reach approximately US$9.30 per kilogram—threefold the current price of Jet A fuel, excluding transportation and operational expenses, which would likely double that figure if used in aviation.
A recent DNV report on offshore green hydrogen production at wind farms, despite its questionable assumptions aimed at promoting hydrogen pipelines, indicated that the lowest possible production cost could be US$3.50 per kilogram before any distribution. This price is significantly higher than liquid natural gas, the most expensive form of energy currently utilized, rendering hydrogen an impractical option for energy storage and transportation.
During the panel discussion, I highlighted a recent review of hydrogen investment opportunities that relied on overly optimistic assumptions regarding electricity costs. One proposal suggested achieving firm electricity prices of US$15 per MWh, which is far from realistic for industrial facilities. Additionally, the complexities of hydrogen production involve numerous components, most of which have already been optimized and commoditized, contradicting claims that manufacturing costs could decline significantly.
The panelists, while knowledgeable, had not conducted their own cost analyses for hydrogen production. Instead, they relied on prevailing assumptions about affordability—an idea that permeates discussions but ultimately undermines the validity of many models and studies.
Section 2.1: Distribution Challenges
Next, we examined hydrogen distribution. The previously mentioned costs are primarily associated with production or, in the case of the DNV study, at the terminus of a hydrogen transmission system before reaching end-users. However, the final leg of distribution is crucial.
Currently, about 85% of hydrogen production occurs at the point of consumption due to the high costs associated with transportation. Airports and their fuel delivery requirements vary significantly. Smaller airports might rely on fuel delivery trucks, while larger facilities would necessitate the construction of hydrogen pipelines, on-site production facilities, storage tanks, and logistical systems to manage the delivery of liquid hydrogen at extremely low temperatures.
Starting with smaller airports, the assumption that they could manage hydrogen fuel deliveries using trucks quickly falls apart. Presently, hydrogen is primarily transported in gaseous form via tube trailers, and the low energy density of gaseous hydrogen necessitates substantial storage systems, significantly limiting the operational range of hydrogen-powered aircraft.
Alternatively, while liquid hydrogen offers advantages for aviation, transporting it poses its own set of challenges. For example, driving trucks filled with liquid hydrogen on warm roads leads to rapid boil-off, complicating logistics. While companies like ZeroAvia claim to have solutions, their operations often involve small demonstrator aircraft funded by investors, raising questions about long-term feasibility.
The cost of delivering gaseous hydrogen via truck in the US and Europe hovers around US$10 per kilogram, making it prohibitively expensive. This reality is reflected in the high prices seen at hydrogen refueling stations, where costs can reach US$25 per kilogram. The energy density of hydrogen is notably lower than that of gasoline, necessitating a far greater number of deliveries to meet demand.
To illustrate, consider the fuel capacity of an Airbus A321, which can hold approximately 24,000 liters of Jet A (around 18 tons). Given that liquid hydrogen has a higher energy density, the equivalent fuel requirement would be about 7.4 tons of liquid hydrogen. Supplying even one aircraft would require multiple truckloads, leading to logistical congestion at airports, further increasing costs and operational complexity.
While hydrogen pipelines exist today, they primarily transport hydrogen from natural gas processing facilities to oil refineries. The longest pipelines are concentrated around refineries, with only about 2,500 km of hydrogen infrastructure in the US.
Given that green hydrogen is unlikely to be produced near airports, distribution distances would increase, exacerbating logistical challenges. Additionally, hydrogen's potential to contribute to global warming through leaks and the necessity for extensive infrastructure upgrades further complicates its viability as an aviation fuel.
Section 2.2: Safety Considerations
Safety is another critical area of concern. Passenger aviation is one of the safest modes of transportation, thanks to extensive data collection and continuous improvement efforts. Any new fuel source must meet rigorous safety standards.
Hydrogen poses unique safety challenges due to its propensity to leak and its broad combustion range compared to conventional fuels. This characteristic heightens the risk of explosive environments in confined spaces, such as aircraft cabins.
While the idea might be to keep hydrogen outside the passenger area, liquid hydrogen must be stored in large, spherical tanks to prevent rapid boil-off, which complicates aircraft design. Traditional fuel storage, such as Jet A, is integrated into aircraft wings, allowing for efficient weight distribution. However, hydrogen’s storage requirements present significant engineering challenges.
There are also concerns about the potential for hydrogen to leak into passenger compartments, creating serious safety hazards. Attempts to develop alternative storage solutions have not proven viable, leaving the aviation industry grappling with the complexities of safely integrating hydrogen into existing aircraft designs.
In addition to these technical hurdles, historical examples of hydrogen management failures, such as leaks during NASA's Artemis missions and the explosion of a hydrogen-fueled bus, highlight the inherent risks associated with hydrogen as a fuel source.
Chapter 3: Certification and Regulation
Certification processes for aircraft are rigorous and time-consuming, often requiring hundreds of millions of dollars and years of validation. The complexities introduced by hydrogen fuel necessitate novel designs and technologies, significantly complicating the certification process.
As it stands, no commercial aircraft currently utilizes hydrogen fuel. The introduction of hydrogen to aviation would require extensive new safety protocols and technologies. Given the high stakes involved, the prospect of certifying hydrogen-powered commercial flights remains bleak.
Section 3.1: Viable Alternatives
If hydrogen were the sole option for decarbonizing aviation, one might consider the trade-offs. However, numerous alternatives exist that are not only viable but also more practical and cost-effective.
Electric aviation is already making strides, with multiple startups developing battery-powered aircraft capable of short to medium-haul flights. Recent advancements in battery technology promise to further enhance range and efficiency, making electric aviation a compelling alternative.
Furthermore, sustainable aviation fuels (SAFs) derived from biomass are rapidly gaining traction. The global market for biofuels is expanding, with significant production capabilities already in place.
In conclusion, while the aviation industry explores hydrogen as a fuel source, it is imperative to recognize the numerous alternatives available. The economic, logistical, and safety challenges associated with hydrogen make it a less favorable option compared to electric and biofuel solutions that are poised to transform the industry.